static void xdp_clear_umem_at_qid(struct net_device *dev, u16 queue_id)
{
	if (queue_id < dev->real_num_rx_queues)
		dev->_rx[queue_id].umem = NULL;
	if (queue_id < dev->real_num_tx_queues)
		dev->_tx[queue_id].umem = NULL;
}


xsk: Add missing check on user supplied headroom size

Add a check that the headroom cannot be larger than the available
space in the chunk. In the current code, a malicious user can set the
headroom to a value larger than the chunk size minus the fixed XDP
headroom. That way packets with a length larger than the supported
size in the umem could get accepted and result in an out-of-bounds
write.

Fixes: c0c77d8fb787 ("xsk: add user memory registration support sockopt")
Reported-by: Bui Quang Minh <minhquangbui99@gmail.com>
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=207225
Link: https://lore.kernel.org/bpf/1586849715-23490-1-git-send-email-magnus.karlsson@intel.com

static void xdp_umem_release(struct xdp_umem *umem)
{
	rtnl_lock();
	xdp_umem_clear_dev(umem);
	rtnl_unlock();

	ida_simple_remove(&umem_ida, umem->id);

	if (umem->fq) {
		xskq_destroy(umem->fq);
		umem->fq = NULL;
	}

	if (umem->cq) {
		xskq_destroy(umem->cq);
		umem->cq = NULL;
	}

	xsk_reuseq_destroy(umem);

	xdp_umem_unmap_pages(umem);
	xdp_umem_unpin_pages(umem);

	kvfree(umem->pages);
	umem->pages = NULL;

	xdp_umem_unaccount_pages(umem);
	kfree(umem);
}

An issue was discovered in the Linux kernel before 5.6.7. xdp_umem_reg in net/xdp/xdp_umem.c has an out-of-bounds write (by a user with the CAP_NET_ADMIN capability) because of a lack of headroom validation.


void xdp_get_umem(struct xdp_umem *umem)
{
	refcount_inc(&umem->users);
}


struct xdp_umem *xdp_get_umem_from_qid(struct net_device *dev,
				       u16 queue_id)
{
	if (queue_id < dev->real_num_rx_queues)
		return dev->_rx[queue_id].umem;
	if (queue_id < dev->real_num_tx_queues)
		return dev->_tx[queue_id].umem;

	return NULL;
}


static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
{
	bool unaligned_chunks = mr->flags & XDP_UMEM_UNALIGNED_CHUNK_FLAG;
	u32 chunk_size = mr->chunk_size, headroom = mr->headroom;
	unsigned int chunks, chunks_per_page;
	u64 addr = mr->addr, size = mr->len;
	int err;

	if (chunk_size < XDP_UMEM_MIN_CHUNK_SIZE || chunk_size > PAGE_SIZE) {
		/* Strictly speaking we could support this, if:
		 * - huge pages, or*
		 * - using an IOMMU, or
		 * - making sure the memory area is consecutive
		 * but for now, we simply say "computer says no".
		 */
		return -EINVAL;
	}

	if (mr->flags & ~(XDP_UMEM_UNALIGNED_CHUNK_FLAG |
			XDP_UMEM_USES_NEED_WAKEUP))
		return -EINVAL;

	if (!unaligned_chunks && !is_power_of_2(chunk_size))
		return -EINVAL;

	if (!PAGE_ALIGNED(addr)) {
		/* Memory area has to be page size aligned. For
		 * simplicity, this might change.
		 */
		return -EINVAL;
	}

	if ((addr + size) < addr)
		return -EINVAL;

	chunks = (unsigned int)div_u64(size, chunk_size);
	if (chunks == 0)
		return -EINVAL;

	if (!unaligned_chunks) {
		chunks_per_page = PAGE_SIZE / chunk_size;
		if (chunks < chunks_per_page || chunks % chunks_per_page)
			return -EINVAL;
	}

	if (headroom >= chunk_size - XDP_PACKET_HEADROOM)
		return -EINVAL;

	umem->address = (unsigned long)addr;
	umem->chunk_mask = unaligned_chunks ? XSK_UNALIGNED_BUF_ADDR_MASK
					    : ~((u64)chunk_size - 1);
	umem->size = size;
	umem->headroom = headroom;
	umem->chunk_size_nohr = chunk_size - headroom;
	umem->npgs = size / PAGE_SIZE;
	umem->pgs = NULL;
	umem->user = NULL;
	umem->flags = mr->flags;
	INIT_LIST_HEAD(&umem->xsk_list);
	spin_lock_init(&umem->xsk_list_lock);

	refcount_set(&umem->users, 1);

	err = xdp_umem_account_pages(umem);
	if (err)
		return err;

	err = xdp_umem_pin_pages(umem);
	if (err)
		goto out_account;

	umem->pages = kvcalloc(umem->npgs, sizeof(*umem->pages),
			       GFP_KERNEL_ACCOUNT);
	if (!umem->pages) {
		err = -ENOMEM;
		goto out_pin;
	}

	err = xdp_umem_map_pages(umem);
	if (!err)
		return 0;

	kvfree(umem->pages);

out_pin:
	xdp_umem_unpin_pages(umem);
out_account:
	xdp_umem_unaccount_pages(umem);
	return err;
}


void xdp_add_sk_umem(struct xdp_umem *umem, struct xdp_sock *xs)
{
	unsigned long flags;

	if (!xs->tx)
		return;

	spin_lock_irqsave(&umem->xsk_list_lock, flags);
	list_add_rcu(&xs->list, &umem->xsk_list);
	spin_unlock_irqrestore(&umem->xsk_list_lock, flags);
}


void xdp_put_umem(struct xdp_umem *umem)
{
	if (!umem)
		return;

	if (refcount_dec_and_test(&umem->users)) {
		INIT_WORK(&umem->work, xdp_umem_release_deferred);
		schedule_work(&umem->work);
	}
}


int xdp_umem_assign_dev(struct xdp_umem *umem, struct net_device *dev,
			u16 queue_id, u16 flags)
{
	bool force_zc, force_copy;
	struct netdev_bpf bpf;
	int err = 0;

	ASSERT_RTNL();

	force_zc = flags & XDP_ZEROCOPY;
	force_copy = flags & XDP_COPY;

	if (force_zc && force_copy)
		return -EINVAL;

	if (xdp_get_umem_from_qid(dev, queue_id))
		return -EBUSY;

	err = xdp_reg_umem_at_qid(dev, umem, queue_id);
	if (err)
		return err;

	umem->dev = dev;
	umem->queue_id = queue_id;

	if (flags & XDP_USE_NEED_WAKEUP) {
		umem->flags |= XDP_UMEM_USES_NEED_WAKEUP;
		/* Tx needs to be explicitly woken up the first time.
		 * Also for supporting drivers that do not implement this
		 * feature. They will always have to call sendto().
		 */
		xsk_set_tx_need_wakeup(umem);
	}

	dev_hold(dev);

	if (force_copy)
		/* For copy-mode, we are done. */
		return 0;

	if (!dev->netdev_ops->ndo_bpf || !dev->netdev_ops->ndo_xsk_wakeup) {
		err = -EOPNOTSUPP;
		goto err_unreg_umem;
	}

	bpf.command = XDP_SETUP_XSK_UMEM;
	bpf.xsk.umem = umem;
	bpf.xsk.queue_id = queue_id;

	err = dev->netdev_ops->ndo_bpf(dev, &bpf);
	if (err)
		goto err_unreg_umem;

	umem->zc = true;
	return 0;

err_unreg_umem:
	if (!force_zc)
		err = 0; /* fallback to copy mode */
	if (err)
		xdp_clear_umem_at_qid(dev, queue_id);
	return err;
}


static int xdp_umem_account_pages(struct xdp_umem *umem)
{
	unsigned long lock_limit, new_npgs, old_npgs;

	if (capable(CAP_IPC_LOCK))
		return 0;

	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
	umem->user = get_uid(current_user());

	do {
		old_npgs = atomic_long_read(&umem->user->locked_vm);
		new_npgs = old_npgs + umem->npgs;
		if (new_npgs > lock_limit) {
			free_uid(umem->user);
			umem->user = NULL;
			return -ENOBUFS;
		}
	} while (atomic_long_cmpxchg(&umem->user->locked_vm, old_npgs,
				     new_npgs) != old_npgs);
	return 0;
}


bool xdp_umem_validate_queues(struct xdp_umem *umem)
{
	return umem->fq && umem->cq;
}


static int xdp_umem_map_pages(struct xdp_umem *umem)
{
	unsigned int i;
	void *addr;

	for (i = 0; i < umem->npgs; i++) {
		if (PageHighMem(umem->pgs[i]))
			addr = vmap(&umem->pgs[i], 1, VM_MAP, PAGE_KERNEL);
		else
			addr = page_address(umem->pgs[i]);

		if (!addr) {
			xdp_umem_unmap_pages(umem);
			return -ENOMEM;
		}

		umem->pages[i].addr = addr;
	}

	return 0;
}


static void xdp_umem_release_deferred(struct work_struct *work)
{
	struct xdp_umem *umem = container_of(work, struct xdp_umem, work);

	xdp_umem_release(umem);
}


static int xdp_umem_pin_pages(struct xdp_umem *umem)
{
	unsigned int gup_flags = FOLL_WRITE;
	long npgs;
	int err;

	umem->pgs = kcalloc(umem->npgs, sizeof(*umem->pgs),
			    GFP_KERNEL | __GFP_NOWARN);
	if (!umem->pgs)
		return -ENOMEM;

	down_read(&current->mm->mmap_sem);
	npgs = pin_user_pages(umem->address, umem->npgs,
			      gup_flags | FOLL_LONGTERM, &umem->pgs[0], NULL);
	up_read(&current->mm->mmap_sem);

	if (npgs != umem->npgs) {
		if (npgs >= 0) {
			umem->npgs = npgs;
			err = -ENOMEM;
			goto out_pin;
		}
		err = npgs;
		goto out_pgs;
	}
	return 0;

out_pin:
	xdp_umem_unpin_pages(umem);
out_pgs:
	kfree(umem->pgs);
	umem->pgs = NULL;
	return err;
}


static void xdp_umem_unmap_pages(struct xdp_umem *umem)
{
	unsigned int i;

	for (i = 0; i < umem->npgs; i++)
		if (PageHighMem(umem->pgs[i]))
			vunmap(umem->pages[i].addr);
}


static void xdp_umem_unpin_pages(struct xdp_umem *umem)
{
	unpin_user_pages_dirty_lock(umem->pgs, umem->npgs, true);

	kfree(umem->pgs);
	umem->pgs = NULL;
}


void xdp_del_sk_umem(struct xdp_umem *umem, struct xdp_sock *xs)
{
	unsigned long flags;

	if (!xs->tx)
		return;

	spin_lock_irqsave(&umem->xsk_list_lock, flags);
	list_del_rcu(&xs->list);
	spin_unlock_irqrestore(&umem->xsk_list_lock, flags);
}


static inline int pri2sev(const int pri)
{
	return pri & 0x07;
}


static inline int pri2fac(const int pri)
{
	unsigned fac = pri >> 3;
	return (fac > 23) ? LOG_FAC_INVLD : fac;
}


mm: thp: make the THP mapcount atomic against __split_huge_pmd_locked()

Write protect anon page faults require an accurate mapcount to decide
if to break the COW or not. This is implemented in the THP path with
reuse_swap_page() ->
page_trans_huge_map_swapcount()/page_trans_huge_mapcount().

If the COW triggers while the other processes sharing the page are
under a huge pmd split, to do an accurate reading, we must ensure the
mapcount isn't computed while it's being transferred from the head
page to the tail pages.

reuse_swap_cache() already runs serialized by the page lock, so it's
enough to add the page lock around __split_huge_pmd_locked too, in
order to add the missing serialization.

Note: the commit in "Fixes" is just to facilitate the backporting,
because the code before such commit didn't try to do an accurate THP
mapcount calculation and it instead used the page_count() to decide if
to COW or not. Both the page_count and the pin_count are THP-wide
refcounts, so they're inaccurate if used in
reuse_swap_page(). Reverting such commit (besides the unrelated fix to
the local anon_vma assignment) would have also opened the window for
memory corruption side effects to certain workloads as documented in
such commit header.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Suggested-by: Jann Horn <jannh@google.com>
Reported-by: Jann Horn <jannh@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: 6d0a07edd17c ("mm: thp: calculate the mapcount correctly for THP pages during WP faults")
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

static ssize_t enabled_store(struct kobject *kobj,
			     struct kobj_attribute *attr,
			     const char *buf, size_t count)
{
	ssize_t ret = count;

	if (sysfs_streq(buf, "always")) {
		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "madvise")) {
		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "never")) {
		clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
	} else
		ret = -EINVAL;

	if (ret > 0) {
		int err = start_stop_khugepaged();
		if (err)
			ret = err;
	}
	return ret;
}

An issue was discovered in __split_huge_pmd in mm/huge_memory.c in the Linux kernel before 5.7.5. The copy-on-write implementation can grant unintended write access because of a race condition in a THP mapcount check, aka CID-c444eb564fb1.


void prep_transhuge_page(struct page *page)
{
	/*
	 * we use page->mapping and page->indexlru in second tail page
	 * as list_head: assuming THP order >= 2
	 */

	INIT_LIST_HEAD(page_deferred_list(page));
	set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
}


void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
		unsigned long address, bool freeze, struct page *page)
{
	spinlock_t *ptl;
	struct mmu_notifier_range range;
	bool was_locked = false;
	pmd_t _pmd;

	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
				address & HPAGE_PMD_MASK,
				(address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
	mmu_notifier_invalidate_range_start(&range);
	ptl = pmd_lock(vma->vm_mm, pmd);

	/*
	 * If caller asks to setup a migration entries, we need a page to check
	 * pmd against. Otherwise we can end up replacing wrong page.
	 */
	VM_BUG_ON(freeze && !page);
	if (page) {
		VM_WARN_ON_ONCE(!PageLocked(page));
		was_locked = true;
		if (page != pmd_page(*pmd))
			goto out;
	}

repeat:
	if (pmd_trans_huge(*pmd)) {
		if (!page) {
			page = pmd_page(*pmd);
			if (unlikely(!trylock_page(page))) {
				get_page(page);
				_pmd = *pmd;
				spin_unlock(ptl);
				lock_page(page);
				spin_lock(ptl);
				if (unlikely(!pmd_same(*pmd, _pmd))) {
					unlock_page(page);
					put_page(page);
					page = NULL;
					goto repeat;
				}
				put_page(page);
			}
		}
		if (PageMlocked(page))
			clear_page_mlock(page);
	} else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
		goto out;
	__split_huge_pmd_locked(vma, pmd, range.start, freeze);
out:
	spin_unlock(ptl);
	if (!was_locked && page)
		unlock_page(page);
	/*
	 * No need to double call mmu_notifier->invalidate_range() callback.
	 * They are 3 cases to consider inside __split_huge_pmd_locked():
	 *  1) pmdp_huge_clear_flush_notify() call invalidate_range() obvious
	 *  2) __split_huge_zero_page_pmd() read only zero page and any write
	 *    fault will trigger a flush_notify before pointing to a new page
	 *    (it is fine if the secondary mmu keeps pointing to the old zero
	 *    page in the meantime)
	 *  3) Split a huge pmd into pte pointing to the same page. No need
	 *     to invalidate secondary tlb entry they are all still valid.
	 *     any further changes to individual pte will notify. So no need
	 *     to call mmu_notifier->invalidate_range()
	 */
	mmu_notifier_invalidate_range_only_end(&range);
}


void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
{
	pud_t entry;
	unsigned long haddr;
	bool write = vmf->flags & FAULT_FLAG_WRITE;

	vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
	if (unlikely(!pud_same(*vmf->pud, orig_pud)))
		goto unlock;

	entry = pud_mkyoung(orig_pud);
	if (write)
		entry = pud_mkdirty(entry);
	haddr = vmf->address & HPAGE_PUD_MASK;
	if (pudp_set_access_flags(vmf->vma, haddr, vmf->pud, entry, write))
		update_mmu_cache_pud(vmf->vma, vmf->address, vmf->pud);

unlock:
	spin_unlock(vmf->ptl);
}


static ssize_t use_zero_page_show(struct kobject *kobj,
		struct kobj_attribute *attr, char *buf)
{
	return single_hugepage_flag_show(kobj, attr, buf,
				TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
}


static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
		unsigned long haddr)
{
	VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
	VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
	VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
	VM_BUG_ON(!pud_trans_huge(*pud) && !pud_devmap(*pud));

	count_vm_event(THP_SPLIT_PUD);

	pudp_huge_clear_flush_notify(vma, haddr, pud);
}


static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
			struct page *page, gfp_t gfp)
{
	struct vm_area_struct *vma = vmf->vma;
	struct mem_cgroup *memcg;
	pgtable_t pgtable;
	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
	vm_fault_t ret = 0;

	VM_BUG_ON_PAGE(!PageCompound(page), page);

	if (mem_cgroup_try_charge_delay(page, vma->vm_mm, gfp, &memcg, true)) {
		put_page(page);
		count_vm_event(THP_FAULT_FALLBACK);
		count_vm_event(THP_FAULT_FALLBACK_CHARGE);
		return VM_FAULT_FALLBACK;
	}

	pgtable = pte_alloc_one(vma->vm_mm);
	if (unlikely(!pgtable)) {
		ret = VM_FAULT_OOM;
		goto release;
	}

	clear_huge_page(page, vmf->address, HPAGE_PMD_NR);
	/*
	 * The memory barrier inside __SetPageUptodate makes sure that
	 * clear_huge_page writes become visible before the set_pmd_at()
	 * write.
	 */
	__SetPageUptodate(page);

	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
	if (unlikely(!pmd_none(*vmf->pmd))) {
		goto unlock_release;
	} else {
		pmd_t entry;

		ret = check_stable_address_space(vma->vm_mm);
		if (ret)
			goto unlock_release;

		/* Deliver the page fault to userland */
		if (userfaultfd_missing(vma)) {
			vm_fault_t ret2;

			spin_unlock(vmf->ptl);
			mem_cgroup_cancel_charge(page, memcg, true);
			put_page(page);
			pte_free(vma->vm_mm, pgtable);
			ret2 = handle_userfault(vmf, VM_UFFD_MISSING);
			VM_BUG_ON(ret2 & VM_FAULT_FALLBACK);
			return ret2;
		}

		entry = mk_huge_pmd(page, vma->vm_page_prot);
		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
		page_add_new_anon_rmap(page, vma, haddr, true);
		mem_cgroup_commit_charge(page, memcg, false, true);
		lru_cache_add_active_or_unevictable(page, vma);
		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
		set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
		add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
		mm_inc_nr_ptes(vma->vm_mm);
		spin_unlock(vmf->ptl);
		count_vm_event(THP_FAULT_ALLOC);
		count_memcg_events(memcg, THP_FAULT_ALLOC, 1);
	}

	return 0;
unlock_release:
	spin_unlock(vmf->ptl);
release:
	if (pgtable)
		pte_free(vma->vm_mm, pgtable);
	mem_cgroup_cancel_charge(page, memcg, true);
	put_page(page);
	return ret;

}


void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
		bool freeze, struct page *page)
{
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;

	pgd = pgd_offset(vma->vm_mm, address);
	if (!pgd_present(*pgd))
		return;

	p4d = p4d_offset(pgd, address);
	if (!p4d_present(*p4d))
		return;

	pud = pud_offset(p4d, address);
	if (!pud_present(*pud))
		return;

	pmd = pmd_offset(pud, address);

	__split_huge_pmd(vma, pmd, address, freeze, page);
}


int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
		 pmd_t *pmd, unsigned long addr)
{
	pmd_t orig_pmd;
	spinlock_t *ptl;

	tlb_change_page_size(tlb, HPAGE_PMD_SIZE);

	ptl = __pmd_trans_huge_lock(pmd, vma);
	if (!ptl)
		return 0;
	/*
	 * For architectures like ppc64 we look at deposited pgtable
	 * when calling pmdp_huge_get_and_clear. So do the
	 * pgtable_trans_huge_withdraw after finishing pmdp related
	 * operations.
	 */
	orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
			tlb->fullmm);
	tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
	if (vma_is_special_huge(vma)) {
		if (arch_needs_pgtable_deposit())
			zap_deposited_table(tlb->mm, pmd);
		spin_unlock(ptl);
		if (is_huge_zero_pmd(orig_pmd))
			tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
	} else if (is_huge_zero_pmd(orig_pmd)) {
		zap_deposited_table(tlb->mm, pmd);
		spin_unlock(ptl);
		tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
	} else {
		struct page *page = NULL;
		int flush_needed = 1;

		if (pmd_present(orig_pmd)) {
			page = pmd_page(orig_pmd);
			page_remove_rmap(page, true);
			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
			VM_BUG_ON_PAGE(!PageHead(page), page);
		} else if (thp_migration_supported()) {
			swp_entry_t entry;

			VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
			entry = pmd_to_swp_entry(orig_pmd);
			page = pfn_to_page(swp_offset(entry));
			flush_needed = 0;
		} else
			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");

		if (PageAnon(page)) {
			zap_deposited_table(tlb->mm, pmd);
			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
		} else {
			if (arch_needs_pgtable_deposit())
				zap_deposited_table(tlb->mm, pmd);
			add_mm_counter(tlb->mm, mm_counter_file(page), -HPAGE_PMD_NR);
		}

		spin_unlock(ptl);
		if (flush_needed)
			tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
	}
	return 1;
}


int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
		unsigned long addr, pgprot_t newprot, unsigned long cp_flags)
{
	struct mm_struct *mm = vma->vm_mm;
	spinlock_t *ptl;
	pmd_t entry;
	bool preserve_write;
	int ret;
	bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
	bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;

	ptl = __pmd_trans_huge_lock(pmd, vma);
	if (!ptl)
		return 0;

	preserve_write = prot_numa && pmd_write(*pmd);
	ret = 1;

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
	if (is_swap_pmd(*pmd)) {
		swp_entry_t entry = pmd_to_swp_entry(*pmd);

		VM_BUG_ON(!is_pmd_migration_entry(*pmd));
		if (is_write_migration_entry(entry)) {
			pmd_t newpmd;
			/*
			 * A protection check is difficult so
			 * just be safe and disable write
			 */
			make_migration_entry_read(&entry);
			newpmd = swp_entry_to_pmd(entry);
			if (pmd_swp_soft_dirty(*pmd))
				newpmd = pmd_swp_mksoft_dirty(newpmd);
			set_pmd_at(mm, addr, pmd, newpmd);
		}
		goto unlock;
	}
#endif

	/*
	 * Avoid trapping faults against the zero page. The read-only
	 * data is likely to be read-cached on the local CPU and
	 * local/remote hits to the zero page are not interesting.
	 */
	if (prot_numa && is_huge_zero_pmd(*pmd))
		goto unlock;

	if (prot_numa && pmd_protnone(*pmd))
		goto unlock;

	/*
	 * In case prot_numa, we are under down_read(mmap_sem). It's critical
	 * to not clear pmd intermittently to avoid race with MADV_DONTNEED
	 * which is also under down_read(mmap_sem):
	 *
	 *	CPU0:				CPU1:
	 *				change_huge_pmd(prot_numa=1)
	 *				 pmdp_huge_get_and_clear_notify()
	 * madvise_dontneed()
	 *  zap_pmd_range()
	 *   pmd_trans_huge(*pmd) == 0 (without ptl)
	 *   // skip the pmd
	 *				 set_pmd_at();
	 *				 // pmd is re-established
	 *
	 * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
	 * which may break userspace.
	 *
	 * pmdp_invalidate() is required to make sure we don't miss
	 * dirty/young flags set by hardware.
	 */
	entry = pmdp_invalidate(vma, addr, pmd);

	entry = pmd_modify(entry, newprot);
	if (preserve_write)
		entry = pmd_mk_savedwrite(entry);
	if (uffd_wp) {
		entry = pmd_wrprotect(entry);
		entry = pmd_mkuffd_wp(entry);
	} else if (uffd_wp_resolve) {
		/*
		 * Leave the write bit to be handled by PF interrupt
		 * handler, then things like COW could be properly
		 * handled.
		 */
		entry = pmd_clear_uffd_wp(entry);
	}
	ret = HPAGE_PMD_NR;
	set_pmd_at(mm, addr, pmd, entry);
	BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
unlock:
	spin_unlock(ptl);
	return ret;
}


spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
{
	spinlock_t *ptl;

	ptl = pud_lock(vma->vm_mm, pud);
	if (likely(pud_trans_huge(*pud) || pud_devmap(*pud)))
		return ptl;
	spin_unlock(ptl);
	return NULL;
}


static struct page *get_huge_zero_page(void)
{
	struct page *zero_page;
retry:
	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
		return READ_ONCE(huge_zero_page);

	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
			HPAGE_PMD_ORDER);
	if (!zero_page) {
		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
		return NULL;
	}
	count_vm_event(THP_ZERO_PAGE_ALLOC);
	preempt_disable();
	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
		preempt_enable();
		__free_pages(zero_page, compound_order(zero_page));
		goto retry;
	}

	/* We take additional reference here. It will be put back by shrinker */
	atomic_set(&huge_zero_refcount, 2);
	preempt_enable();
	return READ_ONCE(huge_zero_page);
}


vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
{
	struct vm_area_struct *vma = vmf->vma;
	struct anon_vma *anon_vma = NULL;
	struct page *page;
	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
	int page_nid = NUMA_NO_NODE, this_nid = numa_node_id();
	int target_nid, last_cpupid = -1;
	bool page_locked;
	bool migrated = false;
	bool was_writable;
	int flags = 0;

	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
	if (unlikely(!pmd_same(pmd, *vmf->pmd)))
		goto out_unlock;

	/*
	 * If there are potential migrations, wait for completion and retry
	 * without disrupting NUMA hinting information. Do not relock and
	 * check_same as the page may no longer be mapped.
	 */
	if (unlikely(pmd_trans_migrating(*vmf->pmd))) {
		page = pmd_page(*vmf->pmd);
		if (!get_page_unless_zero(page))
			goto out_unlock;
		spin_unlock(vmf->ptl);
		put_and_wait_on_page_locked(page);
		goto out;
	}

	page = pmd_page(pmd);
	BUG_ON(is_huge_zero_page(page));
	page_nid = page_to_nid(page);
	last_cpupid = page_cpupid_last(page);
	count_vm_numa_event(NUMA_HINT_FAULTS);
	if (page_nid == this_nid) {
		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
		flags |= TNF_FAULT_LOCAL;
	}

	/* See similar comment in do_numa_page for explanation */
	if (!pmd_savedwrite(pmd))
		flags |= TNF_NO_GROUP;

	/*
	 * Acquire the page lock to serialise THP migrations but avoid dropping
	 * page_table_lock if at all possible
	 */
	page_locked = trylock_page(page);
	target_nid = mpol_misplaced(page, vma, haddr);
	if (target_nid == NUMA_NO_NODE) {
		/* If the page was locked, there are no parallel migrations */
		if (page_locked)
			goto clear_pmdnuma;
	}

	/* Migration could have started since the pmd_trans_migrating check */
	if (!page_locked) {
		page_nid = NUMA_NO_NODE;
		if (!get_page_unless_zero(page))
			goto out_unlock;
		spin_unlock(vmf->ptl);
		put_and_wait_on_page_locked(page);
		goto out;
	}

	/*
	 * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
	 * to serialises splits
	 */
	get_page(page);
	spin_unlock(vmf->ptl);
	anon_vma = page_lock_anon_vma_read(page);

	/* Confirm the PMD did not change while page_table_lock was released */
	spin_lock(vmf->ptl);
	if (unlikely(!pmd_same(pmd, *vmf->pmd))) {
		unlock_page(page);
		put_page(page);
		page_nid = NUMA_NO_NODE;
		goto out_unlock;
	}

	/* Bail if we fail to protect against THP splits for any reason */
	if (unlikely(!anon_vma)) {
		put_page(page);
		page_nid = NUMA_NO_NODE;
		goto clear_pmdnuma;
	}

	/*
	 * Since we took the NUMA fault, we must have observed the !accessible
	 * bit. Make sure all other CPUs agree with that, to avoid them
	 * modifying the page we're about to migrate.
	 *
	 * Must be done under PTL such that we'll observe the relevant
	 * inc_tlb_flush_pending().
	 *
	 * We are not sure a pending tlb flush here is for a huge page
	 * mapping or not. Hence use the tlb range variant
	 */
	if (mm_tlb_flush_pending(vma->vm_mm)) {
		flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
		/*
		 * change_huge_pmd() released the pmd lock before
		 * invalidating the secondary MMUs sharing the primary
		 * MMU pagetables (with ->invalidate_range()). The
		 * mmu_notifier_invalidate_range_end() (which
		 * internally calls ->invalidate_range()) in
		 * change_pmd_range() will run after us, so we can't
		 * rely on it here and we need an explicit invalidate.
		 */
		mmu_notifier_invalidate_range(vma->vm_mm, haddr,
					      haddr + HPAGE_PMD_SIZE);
	}

	/*
	 * Migrate the THP to the requested node, returns with page unlocked
	 * and access rights restored.
	 */
	spin_unlock(vmf->ptl);

	migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
				vmf->pmd, pmd, vmf->address, page, target_nid);
	if (migrated) {
		flags |= TNF_MIGRATED;
		page_nid = target_nid;
	} else
		flags |= TNF_MIGRATE_FAIL;

	goto out;
clear_pmdnuma:
	BUG_ON(!PageLocked(page));
	was_writable = pmd_savedwrite(pmd);
	pmd = pmd_modify(pmd, vma->vm_page_prot);
	pmd = pmd_mkyoung(pmd);
	if (was_writable)
		pmd = pmd_mkwrite(pmd);
	set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
	update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
	unlock_page(page);
out_unlock:
	spin_unlock(vmf->ptl);

out:
	if (anon_vma)
		page_unlock_anon_vma_read(anon_vma);

	if (page_nid != NUMA_NO_NODE)
		task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
				flags);

	return 0;
}


static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
		pud_t *pud, int flags)
{
	pud_t _pud;

	_pud = pud_mkyoung(*pud);
	if (flags & FOLL_WRITE)
		_pud = pud_mkdirty(_pud);
	if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
				pud, _pud, flags & FOLL_WRITE))
		update_mmu_cache_pud(vma, addr, pud);
}


static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
		struct page *zero_page)
{
	pmd_t entry;
	if (!pmd_none(*pmd))
		return false;
	entry = mk_pmd(zero_page, vma->vm_page_prot);
	entry = pmd_mkhuge(entry);
	if (pgtable)
		pgtable_trans_huge_deposit(mm, pmd, pgtable);
	set_pmd_at(mm, haddr, pmd, entry);
	mm_inc_nr_ptes(mm);
	return true;
}


void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
		struct page *page)
{
	struct vm_area_struct *vma = pvmw->vma;
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address = pvmw->address;
	pmd_t pmdval;
	swp_entry_t entry;
	pmd_t pmdswp;

	if (!(pvmw->pmd && !pvmw->pte))
		return;

	flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
	pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
	if (pmd_dirty(pmdval))
		set_page_dirty(page);
	entry = make_migration_entry(page, pmd_write(pmdval));
	pmdswp = swp_entry_to_pmd(entry);
	if (pmd_soft_dirty(pmdval))
		pmdswp = pmd_swp_mksoft_dirty(pmdswp);
	set_pmd_at(mm, address, pvmw->pmd, pmdswp);
	page_remove_rmap(page, true);
	put_page(page);
}


static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
		unsigned long haddr, bool freeze)
{
	struct mm_struct *mm = vma->vm_mm;
	struct page *page;
	pgtable_t pgtable;
	pmd_t old_pmd, _pmd;
	bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
	unsigned long addr;
	int i;

	VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
	VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
	VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
	VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
				&& !pmd_devmap(*pmd));

	count_vm_event(THP_SPLIT_PMD);

	if (!vma_is_anonymous(vma)) {
		_pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
		/*
		 * We are going to unmap this huge page. So
		 * just go ahead and zap it
		 */
		if (arch_needs_pgtable_deposit())
			zap_deposited_table(mm, pmd);
		if (vma_is_special_huge(vma))
			return;
		page = pmd_page(_pmd);
		if (!PageDirty(page) && pmd_dirty(_pmd))
			set_page_dirty(page);
		if (!PageReferenced(page) && pmd_young(_pmd))
			SetPageReferenced(page);
		page_remove_rmap(page, true);
		put_page(page);
		add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
		return;
	} else if (is_huge_zero_pmd(*pmd)) {
		/*
		 * FIXME: Do we want to invalidate secondary mmu by calling
		 * mmu_notifier_invalidate_range() see comments below inside
		 * __split_huge_pmd() ?
		 *
		 * We are going from a zero huge page write protected to zero
		 * small page also write protected so it does not seems useful
		 * to invalidate secondary mmu at this time.
		 */
		return __split_huge_zero_page_pmd(vma, haddr, pmd);
	}

	/*
	 * Up to this point the pmd is present and huge and userland has the
	 * whole access to the hugepage during the split (which happens in
	 * place). If we overwrite the pmd with the not-huge version pointing
	 * to the pte here (which of course we could if all CPUs were bug
	 * free), userland could trigger a small page size TLB miss on the
	 * small sized TLB while the hugepage TLB entry is still established in
	 * the huge TLB. Some CPU doesn't like that.
	 * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
	 * 383 on page 93. Intel should be safe but is also warns that it's
	 * only safe if the permission and cache attributes of the two entries
	 * loaded in the two TLB is identical (which should be the case here).
	 * But it is generally safer to never allow small and huge TLB entries
	 * for the same virtual address to be loaded simultaneously. So instead
	 * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
	 * current pmd notpresent (atomically because here the pmd_trans_huge
	 * must remain set at all times on the pmd until the split is complete
	 * for this pmd), then we flush the SMP TLB and finally we write the
	 * non-huge version of the pmd entry with pmd_populate.
	 */
	old_pmd = pmdp_invalidate(vma, haddr, pmd);

	pmd_migration = is_pmd_migration_entry(old_pmd);
	if (unlikely(pmd_migration)) {
		swp_entry_t entry;

		entry = pmd_to_swp_entry(old_pmd);
		page = pfn_to_page(swp_offset(entry));
		write = is_write_migration_entry(entry);
		young = false;
		soft_dirty = pmd_swp_soft_dirty(old_pmd);
		uffd_wp = pmd_swp_uffd_wp(old_pmd);
	} else {
		page = pmd_page(old_pmd);
		if (pmd_dirty(old_pmd))
			SetPageDirty(page);
		write = pmd_write(old_pmd);
		young = pmd_young(old_pmd);
		soft_dirty = pmd_soft_dirty(old_pmd);
		uffd_wp = pmd_uffd_wp(old_pmd);
	}
	VM_BUG_ON_PAGE(!page_count(page), page);
	page_ref_add(page, HPAGE_PMD_NR - 1);

	/*
	 * Withdraw the table only after we mark the pmd entry invalid.
	 * This's critical for some architectures (Power).
	 */
	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
	pmd_populate(mm, &_pmd, pgtable);

	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
		pte_t entry, *pte;
		/*
		 * Note that NUMA hinting access restrictions are not
		 * transferred to avoid any possibility of altering
		 * permissions across VMAs.
		 */
		if (freeze || pmd_migration) {
			swp_entry_t swp_entry;
			swp_entry = make_migration_entry(page + i, write);
			entry = swp_entry_to_pte(swp_entry);
			if (soft_dirty)
				entry = pte_swp_mksoft_dirty(entry);
			if (uffd_wp)
				entry = pte_swp_mkuffd_wp(entry);
		} else {
			entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
			entry = maybe_mkwrite(entry, vma);
			if (!write)
				entry = pte_wrprotect(entry);
			if (!young)
				entry = pte_mkold(entry);
			if (soft_dirty)
				entry = pte_mksoft_dirty(entry);
			if (uffd_wp)
				entry = pte_mkuffd_wp(entry);
		}
		pte = pte_offset_map(&_pmd, addr);
		BUG_ON(!pte_none(*pte));
		set_pte_at(mm, addr, pte, entry);
		atomic_inc(&page[i]._mapcount);
		pte_unmap(pte);
	}

	/*
	 * Set PG_double_map before dropping compound_mapcount to avoid
	 * false-negative page_mapped().
	 */
	if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
		for (i = 0; i < HPAGE_PMD_NR; i++)
			atomic_inc(&page[i]._mapcount);
	}

	if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
		/* Last compound_mapcount is gone. */
		__dec_node_page_state(page, NR_ANON_THPS);
		if (TestClearPageDoubleMap(page)) {
			/* No need in mapcount reference anymore */
			for (i = 0; i < HPAGE_PMD_NR; i++)
				atomic_dec(&page[i]._mapcount);
		}
	}

	smp_wmb(); /* make pte visible before pmd */
	pmd_populate(mm, pmd, pgtable);

	if (freeze) {
		for (i = 0; i < HPAGE_PMD_NR; i++) {
			page_remove_rmap(page + i, false);
			put_page(page + i);
		}
	}
}


static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
{
}


static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
		pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
		pgtable_t pgtable)
{
	struct mm_struct *mm = vma->vm_mm;
	pmd_t entry;
	spinlock_t *ptl;

	ptl = pmd_lock(mm, pmd);
	if (!pmd_none(*pmd)) {
		if (write) {
			if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
				WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
				goto out_unlock;
			}
			entry = pmd_mkyoung(*pmd);
			entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
			if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
				update_mmu_cache_pmd(vma, addr, pmd);
		}

		goto out_unlock;
	}

	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
	if (pfn_t_devmap(pfn))
		entry = pmd_mkdevmap(entry);
	if (write) {
		entry = pmd_mkyoung(pmd_mkdirty(entry));
		entry = maybe_pmd_mkwrite(entry, vma);
	}

	if (pgtable) {
		pgtable_trans_huge_deposit(mm, pmd, pgtable);
		mm_inc_nr_ptes(mm);
		pgtable = NULL;
	}

	set_pmd_at(mm, addr, pmd, entry);
	update_mmu_cache_pmd(vma, addr, pmd);

out_unlock:
	spin_unlock(ptl);
	if (pgtable)
		pte_free(mm, pgtable);
}


void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
		unsigned long address)
{
	spinlock_t *ptl;
	struct mmu_notifier_range range;

	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
				address & HPAGE_PUD_MASK,
				(address & HPAGE_PUD_MASK) + HPAGE_PUD_SIZE);
	mmu_notifier_invalidate_range_start(&range);
	ptl = pud_lock(vma->vm_mm, pud);
	if (unlikely(!pud_trans_huge(*pud) && !pud_devmap(*pud)))
		goto out;
	__split_huge_pud_locked(vma, pud, range.start);

out:
	spin_unlock(ptl);
	/*
	 * No need to double call mmu_notifier->invalidate_range() callback as
	 * the above pudp_huge_clear_flush_notify() did already call it.
	 */
	mmu_notifier_invalidate_range_only_end(&range);
}


static void __split_huge_page_tail(struct page *head, int tail,
		struct lruvec *lruvec, struct list_head *list)
{
	struct page *page_tail = head + tail;

	VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);

	/*
	 * Clone page flags before unfreezing refcount.
	 *
	 * After successful get_page_unless_zero() might follow flags change,
	 * for exmaple lock_page() which set PG_waiters.
	 */
	page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
	page_tail->flags |= (head->flags &
			((1L << PG_referenced) |
			 (1L << PG_swapbacked) |
			 (1L << PG_swapcache) |
			 (1L << PG_mlocked) |
			 (1L << PG_uptodate) |
			 (1L << PG_active) |
			 (1L << PG_workingset) |
			 (1L << PG_locked) |
			 (1L << PG_unevictable) |
			 (1L << PG_dirty)));

	/* ->mapping in first tail page is compound_mapcount */
	VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
			page_tail);
	page_tail->mapping = head->mapping;
	page_tail->index = head->index + tail;

	/* Page flags must be visible before we make the page non-compound. */
	smp_wmb();

	/*
	 * Clear PageTail before unfreezing page refcount.
	 *
	 * After successful get_page_unless_zero() might follow put_page()
	 * which needs correct compound_head().
	 */
	clear_compound_head(page_tail);

	/* Finally unfreeze refcount. Additional reference from page cache. */
	page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
					  PageSwapCache(head)));

	if (page_is_young(head))
		set_page_young(page_tail);
	if (page_is_idle(head))
		set_page_idle(page_tail);

	page_cpupid_xchg_last(page_tail, page_cpupid_last(head));

	/*
	 * always add to the tail because some iterators expect new
	 * pages to show after the currently processed elements - e.g.
	 * migrate_pages
	 */
	lru_add_page_tail(head, page_tail, lruvec, list);
}


bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
		  unsigned long new_addr, unsigned long old_end,
		  pmd_t *old_pmd, pmd_t *new_pmd)
{
	spinlock_t *old_ptl, *new_ptl;
	pmd_t pmd;
	struct mm_struct *mm = vma->vm_mm;
	bool force_flush = false;

	if ((old_addr & ~HPAGE_PMD_MASK) ||
	    (new_addr & ~HPAGE_PMD_MASK) ||
	    old_end - old_addr < HPAGE_PMD_SIZE)
		return false;

	/*
	 * The destination pmd shouldn't be established, free_pgtables()
	 * should have release it.
	 */
	if (WARN_ON(!pmd_none(*new_pmd))) {
		VM_BUG_ON(pmd_trans_huge(*new_pmd));
		return false;
	}

	/*
	 * We don't have to worry about the ordering of src and dst
	 * ptlocks because exclusive mmap_sem prevents deadlock.
	 */
	old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
	if (old_ptl) {
		new_ptl = pmd_lockptr(mm, new_pmd);
		if (new_ptl != old_ptl)
			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
		pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
		if (pmd_present(pmd))
			force_flush = true;
		VM_BUG_ON(!pmd_none(*new_pmd));

		if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
			pgtable_t pgtable;
			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
		}
		pmd = move_soft_dirty_pmd(pmd);
		set_pmd_at(mm, new_addr, new_pmd, pmd);
		if (force_flush)
			flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
		if (new_ptl != old_ptl)
			spin_unlock(new_ptl);
		spin_unlock(old_ptl);
		return true;
	}
	return false;
}


static void __split_huge_page(struct page *page, struct list_head *list,
		pgoff_t end, unsigned long flags)
{
	struct page *head = compound_head(page);
	pg_data_t *pgdat = page_pgdat(head);
	struct lruvec *lruvec;
	struct address_space *swap_cache = NULL;
	unsigned long offset = 0;
	int i;

	lruvec = mem_cgroup_page_lruvec(head, pgdat);

	/* complete memcg works before add pages to LRU */
	mem_cgroup_split_huge_fixup(head);

	if (PageAnon(head) && PageSwapCache(head)) {
		swp_entry_t entry = { .val = page_private(head) };

		offset = swp_offset(entry);
		swap_cache = swap_address_space(entry);
		xa_lock(&swap_cache->i_pages);
	}

	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
		__split_huge_page_tail(head, i, lruvec, list);
		/* Some pages can be beyond i_size: drop them from page cache */
		if (head[i].index >= end) {
			ClearPageDirty(head + i);
			__delete_from_page_cache(head + i, NULL);
			if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
				shmem_uncharge(head->mapping->host, 1);
			put_page(head + i);
		} else if (!PageAnon(page)) {
			__xa_store(&head->mapping->i_pages, head[i].index,
					head + i, 0);
		} else if (swap_cache) {
			__xa_store(&swap_cache->i_pages, offset + i,
					head + i, 0);
		}
	}

	ClearPageCompound(head);

	split_page_owner(head, HPAGE_PMD_ORDER);

	/* See comment in __split_huge_page_tail() */
	if (PageAnon(head)) {
		/* Additional pin to swap cache */
		if (PageSwapCache(head)) {
			page_ref_add(head, 2);
			xa_unlock(&swap_cache->i_pages);
		} else {
			page_ref_inc(head);
		}
	} else {
		/* Additional pin to page cache */
		page_ref_add(head, 2);
		xa_unlock(&head->mapping->i_pages);
	}

	spin_unlock_irqrestore(&pgdat->lru_lock, flags);

	remap_page(head);

	for (i = 0; i < HPAGE_PMD_NR; i++) {
		struct page *subpage = head + i;
		if (subpage == page)
			continue;
		unlock_page(subpage);

		/*
		 * Subpages may be freed if there wasn't any mapping
		 * like if add_to_swap() is running on a lru page that
		 * had its mapping zapped. And freeing these pages
		 * requires taking the lru_lock so we do the put_page
		 * of the tail pages after the split is complete.
		 */
		put_page(subpage);
	}
}


static void put_huge_zero_page(void)
{
	/*
	 * Counter should never go to zero here. Only shrinker can put
	 * last reference.
	 */
	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
}


struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
				   unsigned long addr,
				   pmd_t *pmd,
				   unsigned int flags)
{
	struct mm_struct *mm = vma->vm_mm;
	struct page *page = NULL;

	assert_spin_locked(pmd_lockptr(mm, pmd));

	if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
		goto out;

	/* Avoid dumping huge zero page */
	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
		return ERR_PTR(-EFAULT);

	/* Full NUMA hinting faults to serialise migration in fault paths */
	if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
		goto out;

	page = pmd_page(*pmd);
	VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);

	if (!try_grab_page(page, flags))
		return ERR_PTR(-ENOMEM);

	if (flags & FOLL_TOUCH)
		touch_pmd(vma, addr, pmd, flags);

	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
		/*
		 * We don't mlock() pte-mapped THPs. This way we can avoid
		 * leaking mlocked pages into non-VM_LOCKED VMAs.
		 *
		 * For anon THP:
		 *
		 * In most cases the pmd is the only mapping of the page as we
		 * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
		 * writable private mappings in populate_vma_page_range().
		 *
		 * The only scenario when we have the page shared here is if we
		 * mlocking read-only mapping shared over fork(). We skip
		 * mlocking such pages.
		 *
		 * For file THP:
		 *
		 * We can expect PageDoubleMap() to be stable under page lock:
		 * for file pages we set it in page_add_file_rmap(), which
		 * requires page to be locked.
		 */

		if (PageAnon(page) && compound_mapcount(page) != 1)
			goto skip_mlock;
		if (PageDoubleMap(page) || !page->mapping)
			goto skip_mlock;
		if (!trylock_page(page))
			goto skip_mlock;
		lru_add_drain();
		if (page->mapping && !PageDoubleMap(page))
			mlock_vma_page(page);
		unlock_page(page);
	}
skip_mlock:
	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
	VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);

out:
	return page;
}


static vm_fault_t do_huge_pmd_wp_page_fallback(struct vm_fault *vmf,
			pmd_t orig_pmd, struct page *page)
{
	struct vm_area_struct *vma = vmf->vma;
	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
	struct mem_cgroup *memcg;
	pgtable_t pgtable;
	pmd_t _pmd;
	int i;
	vm_fault_t ret = 0;
	struct page **pages;
	struct mmu_notifier_range range;

	pages = kmalloc_array(HPAGE_PMD_NR, sizeof(struct page *),
			      GFP_KERNEL);
	if (unlikely(!pages)) {
		ret |= VM_FAULT_OOM;
		goto out;
	}

	for (i = 0; i < HPAGE_PMD_NR; i++) {
		pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE, vma,
					       vmf->address, page_to_nid(page));
		if (unlikely(!pages[i] ||
			     mem_cgroup_try_charge_delay(pages[i], vma->vm_mm,
				     GFP_KERNEL, &memcg, false))) {
			if (pages[i])
				put_page(pages[i]);
			while (--i >= 0) {
				memcg = (void *)page_private(pages[i]);
				set_page_private(pages[i], 0);
				mem_cgroup_cancel_charge(pages[i], memcg,
						false);
				put_page(pages[i]);
			}
			kfree(pages);
			ret |= VM_FAULT_OOM;
			goto out;
		}
		set_page_private(pages[i], (unsigned long)memcg);
	}

	for (i = 0; i < HPAGE_PMD_NR; i++) {
		copy_user_highpage(pages[i], page + i,
				   haddr + PAGE_SIZE * i, vma);
		__SetPageUptodate(pages[i]);
		cond_resched();
	}

	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
				haddr, haddr + HPAGE_PMD_SIZE);
	mmu_notifier_invalidate_range_start(&range);

	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
	if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
		goto out_free_pages;
	VM_BUG_ON_PAGE(!PageHead(page), page);

	/*
	 * Leave pmd empty until pte is filled note we must notify here as
	 * concurrent CPU thread might write to new page before the call to
	 * mmu_notifier_invalidate_range_end() happens which can lead to a
	 * device seeing memory write in different order than CPU.
	 *
	 * See Documentation/vm/mmu_notifier.rst
	 */
	pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);

	pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, vmf->pmd);
	pmd_populate(vma->vm_mm, &_pmd, pgtable);

	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
		pte_t entry;
		entry = mk_pte(pages[i], vma->vm_page_prot);
		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
		memcg = (void *)page_private(pages[i]);
		set_page_private(pages[i], 0);
		page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
		mem_cgroup_commit_charge(pages[i], memcg, false, false);
		lru_cache_add_active_or_unevictable(pages[i], vma);
		vmf->pte = pte_offset_map(&_pmd, haddr);
		VM_BUG_ON(!pte_none(*vmf->pte));
		set_pte_at(vma->vm_mm, haddr, vmf->pte, entry);
		pte_unmap(vmf->pte);
	}
	kfree(pages);

	smp_wmb(); /* make pte visible before pmd */
	pmd_populate(vma->vm_mm, vmf->pmd, pgtable);
	page_remove_rmap(page, true);
	spin_unlock(vmf->ptl);

	/*
	 * No need to double call mmu_notifier->invalidate_range() callback as
	 * the above pmdp_huge_clear_flush_notify() did already call it.
	 */
	mmu_notifier_invalidate_range_only_end(&range);

	ret |= VM_FAULT_WRITE;
	put_page(page);

out:
	return ret;

out_free_pages:
	spin_unlock(vmf->ptl);
	mmu_notifier_invalidate_range_end(&range);
	for (i = 0; i < HPAGE_PMD_NR; i++) {
		memcg = (void *)page_private(pages[i]);
		set_page_private(pages[i], 0);
		mem_cgroup_cancel_charge(pages[i], memcg, false);
		put_page(pages[i]);
	}
	kfree(pages);
	goto out;
}


bool can_split_huge_page(struct page *page, int *pextra_pins)
{
	int extra_pins;

	/* Additional pins from page cache */
	if (PageAnon(page))
		extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
	else
		extra_pins = HPAGE_PMD_NR;
	if (pextra_pins)
		*pextra_pins = extra_pins;
	return total_mapcount(page) == page_count(page) - extra_pins - 1;
}


spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
{
	spinlock_t *ptl;
	ptl = pmd_lock(vma->vm_mm, pmd);
	if (likely(is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) ||
			pmd_devmap(*pmd)))
		return ptl;
	spin_unlock(ptl);
	return NULL;
}


static void remap_page(struct page *page)
{
	int i;
	if (PageTransHuge(page)) {
		remove_migration_ptes(page, page, true);
	} else {
		for (i = 0; i < HPAGE_PMD_NR; i++)
			remove_migration_ptes(page + i, page + i, true);
	}
}


int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
{
	int i, ret, _total_mapcount, mapcount;

	/* hugetlbfs shouldn't call it */
	VM_BUG_ON_PAGE(PageHuge(page), page);

	if (likely(!PageTransCompound(page))) {
		mapcount = atomic_read(&page->_mapcount) + 1;
		if (total_mapcount)
			*total_mapcount = mapcount;
		return mapcount;
	}

	page = compound_head(page);

	_total_mapcount = ret = 0;
	for (i = 0; i < HPAGE_PMD_NR; i++) {
		mapcount = atomic_read(&page[i]._mapcount) + 1;
		ret = max(ret, mapcount);
		_total_mapcount += mapcount;
	}
	if (PageDoubleMap(page)) {
		ret -= 1;
		_total_mapcount -= HPAGE_PMD_NR;
	}
	mapcount = compound_mapcount(page);
	ret += mapcount;
	_total_mapcount += mapcount;
	if (total_mapcount)
		*total_mapcount = _total_mapcount;
	return ret;
}


static unsigned long __thp_get_unmapped_area(struct file *filp,
		unsigned long addr, unsigned long len,
		loff_t off, unsigned long flags, unsigned long size)
{
	loff_t off_end = off + len;
	loff_t off_align = round_up(off, size);
	unsigned long len_pad, ret;

	if (off_end <= off_align || (off_end - off_align) < size)
		return 0;

	len_pad = len + size;
	if (len_pad < len || (off + len_pad) < off)
		return 0;

	ret = current->mm->get_unmapped_area(filp, addr, len_pad,
					      off >> PAGE_SHIFT, flags);

	/*
	 * The failure might be due to length padding. The caller will retry
	 * without the padding.
	 */
	if (IS_ERR_VALUE(ret))
		return 0;

	/*
	 * Do not try to align to THP boundary if allocation at the address
	 * hint succeeds.
	 */
	if (ret == addr)
		return addr;

	ret += (off - ret) & (size - 1);
	return ret;
}


static ssize_t enabled_show(struct kobject *kobj,
			    struct kobj_attribute *attr, char *buf)
{
	if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "[always] madvise never\n");
	else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "always [madvise] never\n");
	else
		return sprintf(buf, "always madvise [never]\n");
}


int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
		  pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
		  struct vm_area_struct *vma)
{
	spinlock_t *dst_ptl, *src_ptl;
	pud_t pud;
	int ret;

	dst_ptl = pud_lock(dst_mm, dst_pud);
	src_ptl = pud_lockptr(src_mm, src_pud);
	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

	ret = -EAGAIN;
	pud = *src_pud;
	if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
		goto out_unlock;

	/*
	 * When page table lock is held, the huge zero pud should not be
	 * under splitting since we don't split the page itself, only pud to
	 * a page table.
	 */
	if (is_huge_zero_pud(pud)) {
		/* No huge zero pud yet */
	}

	pudp_set_wrprotect(src_mm, addr, src_pud);
	pud = pud_mkold(pud_wrprotect(pud));
	set_pud_at(dst_mm, addr, dst_pud, pud);

	ret = 0;
out_unlock:
	spin_unlock(src_ptl);
	spin_unlock(dst_ptl);
	return ret;
}


int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
		 pud_t *pud, unsigned long addr)
{
	spinlock_t *ptl;

	ptl = __pud_trans_huge_lock(pud, vma);
	if (!ptl)
		return 0;
	/*
	 * For architectures like ppc64 we look at deposited pgtable
	 * when calling pudp_huge_get_and_clear. So do the
	 * pgtable_trans_huge_withdraw after finishing pudp related
	 * operations.
	 */
	pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
	tlb_remove_pud_tlb_entry(tlb, pud, addr);
	if (vma_is_special_huge(vma)) {
		spin_unlock(ptl);
		/* No zero page support yet */
	} else {
		/* No support for anonymous PUD pages yet */
		BUG();
	}
	return 1;
}


vm_fault_t vmf_insert_pfn_pud_prot(struct vm_fault *vmf, pfn_t pfn,
				   pgprot_t pgprot, bool write)
{
	unsigned long addr = vmf->address & PUD_MASK;
	struct vm_area_struct *vma = vmf->vma;

	/*
	 * If we had pud_special, we could avoid all these restrictions,
	 * but we need to be consistent with PTEs and architectures that
	 * can't support a 'special' bit.
	 */
	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
			!pfn_t_devmap(pfn));
	BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
						(VM_PFNMAP|VM_MIXEDMAP));
	BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));

	if (addr < vma->vm_start || addr >= vma->vm_end)
		return VM_FAULT_SIGBUS;

	track_pfn_insert(vma, &pgprot, pfn);

	insert_pfn_pud(vma, addr, vmf->pud, pfn, pgprot, write);
	return VM_FAULT_NOPAGE;
}


struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
		pud_t *pud, int flags, struct dev_pagemap **pgmap)
{
	unsigned long pfn = pud_pfn(*pud);
	struct mm_struct *mm = vma->vm_mm;
	struct page *page;

	assert_spin_locked(pud_lockptr(mm, pud));

	if (flags & FOLL_WRITE && !pud_write(*pud))
		return NULL;

	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
			 (FOLL_PIN | FOLL_GET)))
		return NULL;

	if (pud_present(*pud) && pud_devmap(*pud))
		/* pass */;
	else
		return NULL;

	if (flags & FOLL_TOUCH)
		touch_pud(vma, addr, pud, flags);

	/*
	 * device mapped pages can only be returned if the
	 * caller will manage the page reference count.
	 *
	 * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here:
	 */
	if (!(flags & (FOLL_GET | FOLL_PIN)))
		return ERR_PTR(-EEXIST);

	pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
	*pgmap = get_dev_pagemap(pfn, *pgmap);
	if (!*pgmap)
		return ERR_PTR(-EFAULT);
	page = pfn_to_page(pfn);
	if (!try_grab_page(page, flags))
		page = ERR_PTR(-ENOMEM);

	return page;
}


static unsigned long deferred_split_count(struct shrinker *shrink,
		struct shrink_control *sc)
{
	struct pglist_data *pgdata = NODE_DATA(sc->nid);
	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;

#ifdef CONFIG_MEMCG
	if (sc->memcg)
		ds_queue = &sc->memcg->deferred_split_queue;
#endif
	return READ_ONCE(ds_queue->split_queue_len);
}


void vma_adjust_trans_huge(struct vm_area_struct *vma,
			     unsigned long start,
			     unsigned long end,
			     long adjust_next)
{
	/*
	 * If the new start address isn't hpage aligned and it could
	 * previously contain an hugepage: check if we need to split
	 * an huge pmd.
	 */
	if (start & ~HPAGE_PMD_MASK &&
	    (start & HPAGE_PMD_MASK) >= vma->vm_start &&
	    (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
		split_huge_pmd_address(vma, start, false, NULL);

	/*
	 * If the new end address isn't hpage aligned and it could
	 * previously contain an hugepage: check if we need to split
	 * an huge pmd.
	 */
	if (end & ~HPAGE_PMD_MASK &&
	    (end & HPAGE_PMD_MASK) >= vma->vm_start &&
	    (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
		split_huge_pmd_address(vma, end, false, NULL);

	/*
	 * If we're also updating the vma->vm_next->vm_start, if the new
	 * vm_next->vm_start isn't page aligned and it could previously
	 * contain an hugepage: check if we need to split an huge pmd.
	 */
	if (adjust_next > 0) {
		struct vm_area_struct *next = vma->vm_next;
		unsigned long nstart = next->vm_start;
		nstart += adjust_next << PAGE_SHIFT;
		if (nstart & ~HPAGE_PMD_MASK &&
		    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
		    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
			split_huge_pmd_address(next, nstart, false, NULL);
	}
}


int total_mapcount(struct page *page)
{
	int i, compound, ret;

	VM_BUG_ON_PAGE(PageTail(page), page);

	if (likely(!PageCompound(page)))
		return atomic_read(&page->_mapcount) + 1;

	compound = compound_mapcount(page);
	if (PageHuge(page))
		return compound;
	ret = compound;
	for (i = 0; i < HPAGE_PMD_NR; i++)
		ret += atomic_read(&page[i]._mapcount) + 1;
	/* File pages has compound_mapcount included in _mapcount */
	if (!PageAnon(page))
		return ret - compound * HPAGE_PMD_NR;
	if (PageDoubleMap(page))
		ret -= HPAGE_PMD_NR;
	return ret;
}


void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
{
	pmd_t entry;
	unsigned long haddr;
	bool write = vmf->flags & FAULT_FLAG_WRITE;

	vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
	if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
		goto unlock;

	entry = pmd_mkyoung(orig_pmd);
	if (write)
		entry = pmd_mkdirty(entry);
	haddr = vmf->address & HPAGE_PMD_MASK;
	if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
		update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);

unlock:
	spin_unlock(vmf->ptl);
}


bool is_transparent_hugepage(struct page *page)
{
	if (!PageCompound(page))
		return 0;

	page = compound_head(page);
	return is_huge_zero_page(page) ||
	       page[1].compound_dtor == TRANSHUGE_PAGE_DTOR;
}


static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
{
	return 0;
}


bool transparent_hugepage_enabled(struct vm_area_struct *vma)
{
	/* The addr is used to check if the vma size fits */
	unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;

	if (!transhuge_vma_suitable(vma, addr))
		return false;
	if (vma_is_anonymous(vma))
		return __transparent_hugepage_enabled(vma);
	if (vma_is_shmem(vma))
		return shmem_huge_enabled(vma);

	return false;
}


static pmd_t move_soft_dirty_pmd(pmd_t pmd)
{
#ifdef CONFIG_MEM_SOFT_DIRTY
	if (unlikely(is_pmd_migration_entry(pmd)))
		pmd = pmd_swp_mksoft_dirty(pmd);
	else if (pmd_present(pmd))
		pmd = pmd_mksoft_dirty(pmd);
#endif
	return pmd;
}


vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
{
	struct vm_area_struct *vma = vmf->vma;
	struct page *page = NULL, *new_page;
	struct mem_cgroup *memcg;
	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
	struct mmu_notifier_range range;
	gfp_t huge_gfp;			/* for allocation and charge */
	vm_fault_t ret = 0;

	vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
	VM_BUG_ON_VMA(!vma->anon_vma, vma);
	if (is_huge_zero_pmd(orig_pmd))
		goto alloc;
	spin_lock(vmf->ptl);
	if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
		goto out_unlock;

	page = pmd_page(orig_pmd);
	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
	/*
	 * We can only reuse the page if nobody else maps the huge page or it's
	 * part.
	 */
	if (!trylock_page(page)) {
		get_page(page);
		spin_unlock(vmf->ptl);
		lock_page(page);
		spin_lock(vmf->ptl);
		if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
			unlock_page(page);
			put_page(page);
			goto out_unlock;
		}
		put_page(page);
	}
	if (reuse_swap_page(page, NULL)) {
		pmd_t entry;
		entry = pmd_mkyoung(orig_pmd);
		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
		if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
			update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
		ret |= VM_FAULT_WRITE;
		unlock_page(page);
		goto out_unlock;
	}
	unlock_page(page);
	get_page(page);
	spin_unlock(vmf->ptl);
alloc:
	if (__transparent_hugepage_enabled(vma) &&
	    !transparent_hugepage_debug_cow()) {
		huge_gfp = alloc_hugepage_direct_gfpmask(vma);
		new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
	} else
		new_page = NULL;

	if (likely(new_page)) {
		prep_transhuge_page(new_page);
	} else {
		if (!page) {
			split_huge_pmd(vma, vmf->pmd, vmf->address);
			ret |= VM_FAULT_FALLBACK;
		} else {
			ret = do_huge_pmd_wp_page_fallback(vmf, orig_pmd, page);
			if (ret & VM_FAULT_OOM) {
				split_huge_pmd(vma, vmf->pmd, vmf->address);
				ret |= VM_FAULT_FALLBACK;
			}
			put_page(page);
		}
		count_vm_event(THP_FAULT_FALLBACK);
		goto out;
	}

	if (unlikely(mem_cgroup_try_charge_delay(new_page, vma->vm_mm,
					huge_gfp, &memcg, true))) {
		put_page(new_page);
		split_huge_pmd(vma, vmf->pmd, vmf->address);
		if (page)
			put_page(page);
		ret |= VM_FAULT_FALLBACK;
		count_vm_event(THP_FAULT_FALLBACK);
		count_vm_event(THP_FAULT_FALLBACK_CHARGE);
		goto out;
	}

	count_vm_event(THP_FAULT_ALLOC);
	count_memcg_events(memcg, THP_FAULT_ALLOC, 1);

	if (!page)
		clear_huge_page(new_page, vmf->address, HPAGE_PMD_NR);
	else
		copy_user_huge_page(new_page, page, vmf->address,
				    vma, HPAGE_PMD_NR);
	__SetPageUptodate(new_page);

	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
				haddr, haddr + HPAGE_PMD_SIZE);
	mmu_notifier_invalidate_range_start(&range);

	spin_lock(vmf->ptl);
	if (page)
		put_page(page);
	if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
		spin_unlock(vmf->ptl);
		mem_cgroup_cancel_charge(new_page, memcg, true);
		put_page(new_page);
		goto out_mn;
	} else {
		pmd_t entry;
		entry = mk_huge_pmd(new_page, vma->vm_page_prot);
		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
		pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
		page_add_new_anon_rmap(new_page, vma, haddr, true);
		mem_cgroup_commit_charge(new_page, memcg, false, true);
		lru_cache_add_active_or_unevictable(new_page, vma);
		set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
		update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
		if (!page) {
			add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
		} else {
			VM_BUG_ON_PAGE(!PageHead(page), page);
			page_remove_rmap(page, true);
			put_page(page);
		}
		ret |= VM_FAULT_WRITE;
	}
	spin_unlock(vmf->ptl);
out_mn:
	/*
	 * No need to double call mmu_notifier->invalidate_range() callback as
	 * the above pmdp_huge_clear_flush_notify() did already call it.
	 */
	mmu_notifier_invalidate_range_only_end(&range);
out:
	return ret;
out_unlock:
	spin_unlock(vmf->ptl);
	return ret;
}


static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
				       struct shrink_control *sc)
{
	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
		struct page *zero_page = xchg(&huge_zero_page, NULL);
		BUG_ON(zero_page == NULL);
		__free_pages(zero_page, compound_order(zero_page));
		return HPAGE_PMD_NR;
	}

	return 0;
}


pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
{
	if (likely(vma->vm_flags & VM_WRITE))
		pmd = pmd_mkwrite(pmd);
	return pmd;
}


bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
		pmd_t *pmd, unsigned long addr, unsigned long next)
{
	spinlock_t *ptl;
	pmd_t orig_pmd;
	struct page *page;
	struct mm_struct *mm = tlb->mm;
	bool ret = false;

	tlb_change_page_size(tlb, HPAGE_PMD_SIZE);

	ptl = pmd_trans_huge_lock(pmd, vma);
	if (!ptl)
		goto out_unlocked;

	orig_pmd = *pmd;
	if (is_huge_zero_pmd(orig_pmd))
		goto out;

	if (unlikely(!pmd_present(orig_pmd))) {
		VM_BUG_ON(thp_migration_supported() &&
				  !is_pmd_migration_entry(orig_pmd));
		goto out;
	}

	page = pmd_page(orig_pmd);
	/*
	 * If other processes are mapping this page, we couldn't discard
	 * the page unless they all do MADV_FREE so let's skip the page.
	 */
	if (page_mapcount(page) != 1)
		goto out;

	if (!trylock_page(page))
		goto out;

	/*
	 * If user want to discard part-pages of THP, split it so MADV_FREE
	 * will deactivate only them.
	 */
	if (next - addr != HPAGE_PMD_SIZE) {
		get_page(page);
		spin_unlock(ptl);
		split_huge_page(page);
		unlock_page(page);
		put_page(page);
		goto out_unlocked;
	}

	if (PageDirty(page))
		ClearPageDirty(page);
	unlock_page(page);

	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
		pmdp_invalidate(vma, addr, pmd);
		orig_pmd = pmd_mkold(orig_pmd);
		orig_pmd = pmd_mkclean(orig_pmd);

		set_pmd_at(mm, addr, pmd, orig_pmd);
		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
	}

	mark_page_lazyfree(page);
	ret = true;
out:
	spin_unlock(ptl);
out_unlocked:
	return ret;
}


static unsigned long deferred_split_scan(struct shrinker *shrink,
		struct shrink_control *sc)
{
	struct pglist_data *pgdata = NODE_DATA(sc->nid);
	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
	unsigned long flags;
	LIST_HEAD(list), *pos, *next;
	struct page *page;
	int split = 0;

#ifdef CONFIG_MEMCG
	if (sc->memcg)
		ds_queue = &sc->memcg->deferred_split_queue;
#endif

	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
	/* Take pin on all head pages to avoid freeing them under us */
	list_for_each_safe(pos, next, &ds_queue->split_queue) {
		page = list_entry((void *)pos, struct page, mapping);
		page = compound_head(page);
		if (get_page_unless_zero(page)) {
			list_move(page_deferred_list(page), &list);
		} else {
			/* We lost race with put_compound_page() */
			list_del_init(page_deferred_list(page));
			ds_queue->split_queue_len--;
		}
		if (!--sc->nr_to_scan)
			break;
	}
	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);

	list_for_each_safe(pos, next, &list) {
		page = list_entry((void *)pos, struct page, mapping);
		if (!trylock_page(page))
			goto next;
		/* split_huge_page() removes page from list on success */
		if (!split_huge_page(page))
			split++;
		unlock_page(page);
next:
		put_page(page);
	}

	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
	list_splice_tail(&list, &ds_queue->split_queue);
	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);

	/*
	 * Stop shrinker if we didn't split any page, but the queue is empty.
	 * This can happen if pages were freed under us.
	 */
	if (!split && list_empty(&ds_queue->split_queue))
		return SHRINK_STOP;
	return split;
}


static ssize_t debug_cow_show(struct kobject *kobj,
				struct kobj_attribute *attr, char *buf)
{
	return single_hugepage_flag_show(kobj, attr, buf,
				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
}


void mm_put_huge_zero_page(struct mm_struct *mm)
{
	if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
		put_huge_zero_page();
}


struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
		pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
{
	unsigned long pfn = pmd_pfn(*pmd);
	struct mm_struct *mm = vma->vm_mm;
	struct page *page;

	assert_spin_locked(pmd_lockptr(mm, pmd));

	/*
	 * When we COW a devmap PMD entry, we split it into PTEs, so we should
	 * not be in this function with `flags & FOLL_COW` set.
	 */
	WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");

	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
			 (FOLL_PIN | FOLL_GET)))
		return NULL;

	if (flags & FOLL_WRITE && !pmd_write(*pmd))
		return NULL;

	if (pmd_present(*pmd) && pmd_devmap(*pmd))
		/* pass */;
	else
		return NULL;

	if (flags & FOLL_TOUCH)
		touch_pmd(vma, addr, pmd, flags);

	/*
	 * device mapped pages can only be returned if the
	 * caller will manage the page reference count.
	 */
	if (!(flags & (FOLL_GET | FOLL_PIN)))
		return ERR_PTR(-EEXIST);

	pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
	*pgmap = get_dev_pagemap(pfn, *pgmap);
	if (!*pgmap)
		return ERR_PTR(-EFAULT);
	page = pfn_to_page(pfn);
	if (!try_grab_page(page, flags))
		page = ERR_PTR(-ENOMEM);

	return page;
}


static ssize_t hpage_pmd_size_show(struct kobject *kobj,
		struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
}


int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
		  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
		  struct vm_area_struct *vma)
{
	spinlock_t *dst_ptl, *src_ptl;
	struct page *src_page;
	pmd_t pmd;
	pgtable_t pgtable = NULL;
	int ret = -ENOMEM;

	/* Skip if can be re-fill on fault */
	if (!vma_is_anonymous(vma))
		return 0;

	pgtable = pte_alloc_one(dst_mm);
	if (unlikely(!pgtable))
		goto out;

	dst_ptl = pmd_lock(dst_mm, dst_pmd);
	src_ptl = pmd_lockptr(src_mm, src_pmd);
	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

	ret = -EAGAIN;
	pmd = *src_pmd;

	/*
	 * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
	 * does not have the VM_UFFD_WP, which means that the uffd
	 * fork event is not enabled.
	 */
	if (!(vma->vm_flags & VM_UFFD_WP))
		pmd = pmd_clear_uffd_wp(pmd);

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
	if (unlikely(is_swap_pmd(pmd))) {
		swp_entry_t entry = pmd_to_swp_entry(pmd);

		VM_BUG_ON(!is_pmd_migration_entry(pmd));
		if (is_write_migration_entry(entry)) {
			make_migration_entry_read(&entry);
			pmd = swp_entry_to_pmd(entry);
			if (pmd_swp_soft_dirty(*src_pmd))
				pmd = pmd_swp_mksoft_dirty(pmd);
			set_pmd_at(src_mm, addr, src_pmd, pmd);
		}
		add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
		mm_inc_nr_ptes(dst_mm);
		pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
		set_pmd_at(dst_mm, addr, dst_pmd, pmd);
		ret = 0;
		goto out_unlock;
	}
#endif

	if (unlikely(!pmd_trans_huge(pmd))) {
		pte_free(dst_mm, pgtable);
		goto out_unlock;
	}
	/*
	 * When page table lock is held, the huge zero pmd should not be
	 * under splitting since we don't split the page itself, only pmd to
	 * a page table.
	 */
	if (is_huge_zero_pmd(pmd)) {
		struct page *zero_page;
		/*
		 * get_huge_zero_page() will never allocate a new page here,
		 * since we already have a zero page to copy. It just takes a
		 * reference.
		 */
		zero_page = mm_get_huge_zero_page(dst_mm);
		set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
				zero_page);
		ret = 0;
		goto out_unlock;
	}

	src_page = pmd_page(pmd);
	VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
	get_page(src_page);
	page_dup_rmap(src_page, true);
	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
	mm_inc_nr_ptes(dst_mm);
	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);

	pmdp_set_wrprotect(src_mm, addr, src_pmd);
	pmd = pmd_mkold(pmd_wrprotect(pmd));
	set_pmd_at(dst_mm, addr, dst_pmd, pmd);

	ret = 0;
out_unlock:
	spin_unlock(src_ptl);
	spin_unlock(dst_ptl);
out:
	return ret;
}


void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
{
	struct vm_area_struct *vma = pvmw->vma;
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address = pvmw->address;
	unsigned long mmun_start = address & HPAGE_PMD_MASK;
	pmd_t pmde;
	swp_entry_t entry;

	if (!(pvmw->pmd && !pvmw->pte))
		return;

	entry = pmd_to_swp_entry(*pvmw->pmd);
	get_page(new);
	pmde = pmd_mkold(mk_huge_pmd(new, vma->vm_page_prot));
	if (pmd_swp_soft_dirty(*pvmw->pmd))
		pmde = pmd_mksoft_dirty(pmde);
	if (is_write_migration_entry(entry))
		pmde = maybe_pmd_mkwrite(pmde, vma);

	flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE);
	if (PageAnon(new))
		page_add_anon_rmap(new, vma, mmun_start, true);
	else
		page_add_file_rmap(new, true);
	set_pmd_at(mm, mmun_start, pvmw->pmd, pmde);
	if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new))
		mlock_vma_page(new);
	update_mmu_cache_pmd(vma, address, pvmw->pmd);
}


static int __init split_huge_pages_debugfs(void)
{
	debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
			    &split_huge_pages_fops);
	return 0;
}


unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
		unsigned long len, unsigned long pgoff, unsigned long flags)
{
	unsigned long ret;
	loff_t off = (loff_t)pgoff << PAGE_SHIFT;

	if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
		goto out;

	ret = __thp_get_unmapped_area(filp, addr, len, off, flags, PMD_SIZE);
	if (ret)
		return ret;
out:
	return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
}


static inline struct deferred_split *get_deferred_split_queue(struct page *page)
{
	struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));

	return &pgdat->deferred_split_queue;
}


static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
{
	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);

	/* Always do synchronous compaction */
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
		return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);

	/* Kick kcompactd and fail quickly */
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
		return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;

	/* Synchronous compaction if madvised, otherwise kick kcompactd */
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
		return GFP_TRANSHUGE_LIGHT |
			(vma_madvised ? __GFP_DIRECT_RECLAIM :
					__GFP_KSWAPD_RECLAIM);

	/* Only do synchronous compaction if madvised */
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
		return GFP_TRANSHUGE_LIGHT |
		       (vma_madvised ? __GFP_DIRECT_RECLAIM : 0);

	return GFP_TRANSHUGE_LIGHT;
}


static ssize_t defrag_show(struct kobject *kobj,
			   struct kobj_attribute *attr, char *buf)
{
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "[always] defer defer+madvise madvise never\n");
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "always [defer] defer+madvise madvise never\n");
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "always defer [defer+madvise] madvise never\n");
	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
		return sprintf(buf, "always defer defer+madvise [madvise] never\n");
	return sprintf(buf, "always defer defer+madvise madvise [never]\n");
}


static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
{
	int err;

	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
	if (unlikely(!*hugepage_kobj)) {
		pr_err("failed to create transparent hugepage kobject\n");
		return -ENOMEM;
	}

	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
	if (err) {
		pr_err("failed to register transparent hugepage group\n");
		goto delete_obj;
	}

	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
	if (err) {
		pr_err("failed to register transparent hugepage group\n");
		goto remove_hp_group;
	}

	return 0;

remove_hp_group:
	sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
delete_obj:
	kobject_put(*hugepage_kobj);
	return err;
}


int split_huge_page_to_list(struct page *page, struct list_head *list)
{
	struct page *head = compound_head(page);
	struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
	struct deferred_split *ds_queue = get_deferred_split_queue(head);
	struct anon_vma *anon_vma = NULL;
	struct address_space *mapping = NULL;
	int count, mapcount, extra_pins, ret;
	bool mlocked;
	unsigned long flags;
	pgoff_t end;

	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
	VM_BUG_ON_PAGE(!PageLocked(head), head);
	VM_BUG_ON_PAGE(!PageCompound(head), head);

	if (PageWriteback(head))
		return -EBUSY;

	if (PageAnon(head)) {
		/*
		 * The caller does not necessarily hold an mmap_sem that would
		 * prevent the anon_vma disappearing so we first we take a
		 * reference to it and then lock the anon_vma for write. This
		 * is similar to page_lock_anon_vma_read except the write lock
		 * is taken to serialise against parallel split or collapse
		 * operations.
		 */
		anon_vma = page_get_anon_vma(head);
		if (!anon_vma) {
			ret = -EBUSY;
			goto out;
		}
		end = -1;
		mapping = NULL;
		anon_vma_lock_write(anon_vma);
	} else {
		mapping = head->mapping;

		/* Truncated ? */
		if (!mapping) {
			ret = -EBUSY;
			goto out;
		}

		anon_vma = NULL;
		i_mmap_lock_read(mapping);

		/*
		 *__split_huge_page() may need to trim off pages beyond EOF:
		 * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
		 * which cannot be nested inside the page tree lock. So note
		 * end now: i_size itself may be changed at any moment, but
		 * head page lock is good enough to serialize the trimming.
		 */
		end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
	}

	/*
	 * Racy check if we can split the page, before unmap_page() will
	 * split PMDs
	 */
	if (!can_split_huge_page(head, &extra_pins)) {
		ret = -EBUSY;
		goto out_unlock;
	}

	mlocked = PageMlocked(head);
	unmap_page(head);
	VM_BUG_ON_PAGE(compound_mapcount(head), head);

	/* Make sure the page is not on per-CPU pagevec as it takes pin */
	if (mlocked)
		lru_add_drain();

	/* prevent PageLRU to go away from under us, and freeze lru stats */
	spin_lock_irqsave(&pgdata->lru_lock, flags);

	if (mapping) {
		XA_STATE(xas, &mapping->i_pages, page_index(head));

		/*
		 * Check if the head page is present in page cache.
		 * We assume all tail are present too, if head is there.
		 */
		xa_lock(&mapping->i_pages);
		if (xas_load(&xas) != head)
			goto fail;
	}

	/* Prevent deferred_split_scan() touching ->_refcount */
	spin_lock(&ds_queue->split_queue_lock);
	count = page_count(head);
	mapcount = total_mapcount(head);
	if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
		if (!list_empty(page_deferred_list(head))) {
			ds_queue->split_queue_len--;
			list_del(page_deferred_list(head));
		}
		spin_unlock(&ds_queue->split_queue_lock);
		if (mapping) {
			if (PageSwapBacked(head))
				__dec_node_page_state(head, NR_SHMEM_THPS);
			else
				__dec_node_page_state(head, NR_FILE_THPS);
		}

		__split_huge_page(page, list, end, flags);
		if (PageSwapCache(head)) {
			swp_entry_t entry = { .val = page_private(head) };

			ret = split_swap_cluster(entry);
		} else
			ret = 0;
	} else {
		if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
			pr_alert("total_mapcount: %u, page_count(): %u\n",
					mapcount, count);
			if (PageTail(page))
				dump_page(head, NULL);
			dump_page(page, "total_mapcount(head) > 0");
			BUG();
		}
		spin_unlock(&ds_queue->split_queue_lock);
fail:		if (mapping)
			xa_unlock(&mapping->i_pages);
		spin_unlock_irqrestore(&pgdata->lru_lock, flags);
		remap_page(head);
		ret = -EBUSY;
	}

out_unlock:
	if (anon_vma) {
		anon_vma_unlock_write(anon_vma);
		put_anon_vma(anon_vma);
	}
	if (mapping)
		i_mmap_unlock_read(mapping);
out:
	count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
	return ret;
}


static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
		pmd_t *pmd, int flags)
{
	pmd_t _pmd;

	_pmd = pmd_mkyoung(*pmd);
	if (flags & FOLL_WRITE)
		_pmd = pmd_mkdirty(_pmd);
	if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
				pmd, _pmd, flags & FOLL_WRITE))
		update_mmu_cache_pmd(vma, addr, pmd);
}


static ssize_t debug_cow_store(struct kobject *kobj,
			       struct kobj_attribute *attr,
			       const char *buf, size_t count)
{
	return single_hugepage_flag_store(kobj, attr, buf, count,
				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
}


static int __init hugepage_init(void)
{
	int err;
	struct kobject *hugepage_kobj;

	if (!has_transparent_hugepage()) {
		transparent_hugepage_flags = 0;
		return -EINVAL;
	}

	/*
	 * hugepages can't be allocated by the buddy allocator
	 */
	MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
	/*
	 * we use page->mapping and page->index in second tail page
	 * as list_head: assuming THP order >= 2
	 */
	MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);

	err = hugepage_init_sysfs(&hugepage_kobj);
	if (err)
		goto err_sysfs;

	err = khugepaged_init();
	if (err)
		goto err_slab;

	err = register_shrinker(&huge_zero_page_shrinker);
	if (err)
		goto err_hzp_shrinker;
	err = register_shrinker(&deferred_split_shrinker);
	if (err)
		goto err_split_shrinker;

	/*
	 * By default disable transparent hugepages on smaller systems,
	 * where the extra memory used could hurt more than TLB overhead
	 * is likely to save.  The admin can still enable it through /sys.
	 */
	if (totalram_pages() < (512 << (20 - PAGE_SHIFT))) {
		transparent_hugepage_flags = 0;
		return 0;
	}

	err = start_stop_khugepaged();
	if (err)
		goto err_khugepaged;

	return 0;
err_khugepaged:
	unregister_shrinker(&deferred_split_shrinker);
err_split_shrinker:
	unregister_shrinker(&huge_zero_page_shrinker);
err_hzp_shrinker:
	khugepaged_destroy();
err_slab:
	hugepage_exit_sysfs(hugepage_kobj);
err_sysfs:
	return err;
}


static ssize_t defrag_store(struct kobject *kobj,
			    struct kobj_attribute *attr,
			    const char *buf, size_t count)
{
	if (sysfs_streq(buf, "always")) {
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "defer+madvise")) {
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "defer")) {
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "madvise")) {
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
	} else if (sysfs_streq(buf, "never")) {
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
	} else
		return -EINVAL;

	return count;
}


static int __init setup_transparent_hugepage(char *str)
{
	int ret = 0;
	if (!str)
		goto out;
	if (!strcmp(str, "always")) {
		set_bit(TRANSPARENT_HUGEPAGE_FLAG,
			&transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
			  &transparent_hugepage_flags);
		ret = 1;
	} else if (!strcmp(str, "madvise")) {
		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
			  &transparent_hugepage_flags);
		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
			&transparent_hugepage_flags);
		ret = 1;
	} else if (!strcmp(str, "never")) {
		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
			  &transparent_hugepage_flags);
		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
			  &transparent_hugepage_flags);
		ret = 1;
	}
out:
	if (!ret)
		pr_warn("transparent_hugepage= cannot parse, ignored\n");
	return ret;
}


static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
{
	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
	kobject_put(hugepage_kobj);
}


vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
{
	struct vm_area_struct *vma = vmf->vma;
	gfp_t gfp;
	struct page *page;
	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;

	if (!transhuge_vma_suitable(vma, haddr))
		return VM_FAULT_FALLBACK;
	if (unlikely(anon_vma_prepare(vma)))
		return VM_FAULT_OOM;
	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
		return VM_FAULT_OOM;
	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
			!mm_forbids_zeropage(vma->vm_mm) &&
			transparent_hugepage_use_zero_page()) {
		pgtable_t pgtable;
		struct page *zero_page;
		bool set;
		vm_fault_t ret;
		pgtable = pte_alloc_one(vma->vm_mm);
		if (unlikely(!pgtable))
			return VM_FAULT_OOM;
		zero_page = mm_get_huge_zero_page(vma->vm_mm);
		if (unlikely(!zero_page)) {
			pte_free(vma->vm_mm, pgtable);
			count_vm_event(THP_FAULT_FALLBACK);
			return VM_FAULT_FALLBACK;
		}
		vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
		ret = 0;
		set = false;
		if (pmd_none(*vmf->pmd)) {
			ret = check_stable_address_space(vma->vm_mm);
			if (ret) {
				spin_unlock(vmf->ptl);
			} else if (userfaultfd_missing(vma)) {
				spin_unlock(vmf->ptl);
				ret = handle_userfault(vmf, VM_UFFD_MISSING);
				VM_BUG_ON(ret & VM_FAULT_FALLBACK);
			} else {
				set_huge_zero_page(pgtable, vma->vm_mm, vma,
						   haddr, vmf->pmd, zero_page);
				spin_unlock(vmf->ptl);
				set = true;
			}
		} else
			spin_unlock(vmf->ptl);
		if (!set)
			pte_free(vma->vm_mm, pgtable);
		return ret;
	}
	gfp = alloc_hugepage_direct_gfpmask(vma);
	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
	if (unlikely(!page)) {
		count_vm_event(THP_FAULT_FALLBACK);
		return VM_FAULT_FALLBACK;
	}
	prep_transhuge_page(page);
	return __do_huge_pmd_anonymous_page(vmf, page, gfp);
}


ssize_t single_hugepage_flag_show(struct kobject *kobj,
				struct kobj_attribute *attr, char *buf,
				enum transparent_hugepage_flag flag)
{
	return sprintf(buf, "%d\n",
		       !!test_bit(flag, &transparent_hugepage_flags));
}


static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
		unsigned long haddr, pmd_t *pmd)
{
	struct mm_struct *mm = vma->vm_mm;
	pgtable_t pgtable;
	pmd_t _pmd;
	int i;

	/*
	 * Leave pmd empty until pte is filled note that it is fine to delay
	 * notification until mmu_notifier_invalidate_range_end() as we are
	 * replacing a zero pmd write protected page with a zero pte write
	 * protected page.
	 *
	 * See Documentation/vm/mmu_notifier.rst
	 */
	pmdp_huge_clear_flush(vma, haddr, pmd);

	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
	pmd_populate(mm, &_pmd, pgtable);

	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
		pte_t *pte, entry;
		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
		entry = pte_mkspecial(entry);
		pte = pte_offset_map(&_pmd, haddr);
		VM_BUG_ON(!pte_none(*pte));
		set_pte_at(mm, haddr, pte, entry);
		pte_unmap(pte);
	}
	smp_wmb(); /* make pte visible before pmd */
	pmd_populate(mm, pmd, pgtable);
}


void deferred_split_huge_page(struct page *page)
{
	struct deferred_split *ds_queue = get_deferred_split_queue(page);
#ifdef CONFIG_MEMCG
	struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
#endif
	unsigned long flags;

	VM_BUG_ON_PAGE(!PageTransHuge(page), page);

	/*
	 * The try_to_unmap() in page reclaim path might reach here too,
	 * this may cause a race condition to corrupt deferred split queue.
	 * And, if page reclaim is already handling the same page, it is
	 * unnecessary to handle it again in shrinker.
	 *
	 * Check PageSwapCache to determine if the page is being
	 * handled by page reclaim since THP swap would add the page into
	 * swap cache before calling try_to_unmap().
	 */
	if (PageSwapCache(page))
		return;

	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
	if (list_empty(page_deferred_list(page))) {
		count_vm_event(THP_DEFERRED_SPLIT_PAGE);
		list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
		ds_queue->split_queue_len++;
#ifdef CONFIG_MEMCG
		if (memcg)
			memcg_set_shrinker_bit(memcg, page_to_nid(page),
					       deferred_split_shrinker.id);
#endif
	}
	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
}


struct page *mm_get_huge_zero_page(struct mm_struct *mm)
{
	if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
		return READ_ONCE(huge_zero_page);

	if (!get_huge_zero_page())
		return NULL;

	if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
		put_huge_zero_page();

	return READ_ONCE(huge_zero_page);
}


static ssize_t use_zero_page_store(struct kobject *kobj,
		struct kobj_attribute *attr, const char *buf, size_t count)
{
	return single_hugepage_flag_store(kobj, attr, buf, count,
				 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
}


ssize_t single_hugepage_flag_store(struct kobject *kobj,
				 struct kobj_attribute *attr,
				 const char *buf, size_t count,
				 enum transparent_hugepage_flag flag)
{
	unsigned long value;
	int ret;

	ret = kstrtoul(buf, 10, &value);
	if (ret < 0)
		return ret;
	if (value > 1)
		return -EINVAL;

	if (value)
		set_bit(flag, &transparent_hugepage_flags);
	else
		clear_bit(flag, &transparent_hugepage_flags);

	return count;
}


static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
		pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)
{
	struct mm_struct *mm = vma->vm_mm;
	pud_t entry;
	spinlock_t *ptl;

	ptl = pud_lock(mm, pud);
	if (!pud_none(*pud)) {
		if (write) {
			if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
				WARN_ON_ONCE(!is_huge_zero_pud(*pud));
				goto out_unlock;
			}
			entry = pud_mkyoung(*pud);
			entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
			if (pudp_set_access_flags(vma, addr, pud, entry, 1))
				update_mmu_cache_pud(vma, addr, pud);
		}
		goto out_unlock;
	}

	entry = pud_mkhuge(pfn_t_pud(pfn, prot));
	if (pfn_t_devmap(pfn))
		entry = pud_mkdevmap(entry);
	if (write) {
		entry = pud_mkyoung(pud_mkdirty(entry));
		entry = maybe_pud_mkwrite(entry, vma);
	}
	set_pud_at(mm, addr, pud, entry);
	update_mmu_cache_pud(vma, addr, pud);

out_unlock:
	spin_unlock(ptl);
}


void free_transhuge_page(struct page *page)
{
	struct deferred_split *ds_queue = get_deferred_split_queue(page);
	unsigned long flags;

	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
	if (!list_empty(page_deferred_list(page))) {
		ds_queue->split_queue_len--;
		list_del(page_deferred_list(page));
	}
	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
	free_compound_page(page);
}


static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
					struct shrink_control *sc)
{
	/* we can free zero page only if last reference remains */
	return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
}


static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
{
	pgtable_t pgtable;

	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
	pte_free(mm, pgtable);
	mm_dec_nr_ptes(mm);
}


static inline struct deferred_split *get_deferred_split_queue(struct page *page)
{
	struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
	struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));

	if (memcg)
		return &memcg->deferred_split_queue;
	else
		return &pgdat->deferred_split_queue;
}


static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
{
	return pmd_write(pmd) || ((flags & FOLL_COW) && pmd_dirty(pmd));
}


static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
					 spinlock_t *old_pmd_ptl,
					 struct vm_area_struct *vma)
{
	/*
	 * With split pmd lock we also need to move preallocated
	 * PTE page table if new_pmd is on different PMD page table.
	 *
	 * We also don't deposit and withdraw tables for file pages.
	 */
	return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
}


static void unmap_page(struct page *page)
{
	enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
		TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
	bool unmap_success;

	VM_BUG_ON_PAGE(!PageHead(page), page);

	if (PageAnon(page))
		ttu_flags |= TTU_SPLIT_FREEZE;

	unmap_success = try_to_unmap(page, ttu_flags);
	VM_BUG_ON_PAGE(!unmap_success, page);
}


static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
{
	if (likely(vma->vm_flags & VM_WRITE))
		pud = pud_mkwrite(pud);
	return pud;
}


vm_fault_t vmf_insert_pfn_pmd_prot(struct vm_fault *vmf, pfn_t pfn,
				   pgprot_t pgprot, bool write)
{
	unsigned long addr = vmf->address & PMD_MASK;
	struct vm_area_struct *vma = vmf->vma;
	pgtable_t pgtable = NULL;

	/*
	 * If we had pmd_special, we could avoid all these restrictions,
	 * but we need to be consistent with PTEs and architectures that
	 * can't support a 'special' bit.
	 */
	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
			!pfn_t_devmap(pfn));
	BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
						(VM_PFNMAP|VM_MIXEDMAP));
	BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));

	if (addr < vma->vm_start || addr >= vma->vm_end)
		return VM_FAULT_SIGBUS;

	if (arch_needs_pgtable_deposit()) {
		pgtable = pte_alloc_one(vma->vm_mm);
		if (!pgtable)
			return VM_FAULT_OOM;
	}

	track_pfn_insert(vma, &pgprot, pfn);

	insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable);
	return VM_FAULT_NOPAGE;
}


static int split_huge_pages_set(void *data, u64 val)
{
	struct zone *zone;
	struct page *page;
	unsigned long pfn, max_zone_pfn;
	unsigned long total = 0, split = 0;

	if (val != 1)
		return -EINVAL;

	for_each_populated_zone(zone) {
		max_zone_pfn = zone_end_pfn(zone);
		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
			if (!pfn_valid(pfn))
				continue;

			page = pfn_to_page(pfn);
			if (!get_page_unless_zero(page))
				continue;

			if (zone != page_zone(page))
				goto next;

			if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
				goto next;

			total++;
			lock_page(page);
			if (!split_huge_page(page))
				split++;
			unlock_page(page);
next:
			put_page(page);
		}
	}

	pr_info("%lu of %lu THP split\n", split, total);

	return 0;
}