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Commit 176ba4c1 authored by Baolin Wang's avatar Baolin Wang Committed by Greg Kroah-Hartman
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mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page 

commit fac35ba763ed07ba93154c95ffc0c4a55023707f upstream.

On some architectures (like ARM64), it can support CONT-PTE/PMD size
hugetlb, which means it can support not only PMD/PUD size hugetlb (2M and
1G), but also CONT-PTE/PMD size(64K and 32M) if a 4K page size specified.

So when looking up a CONT-PTE size hugetlb page by follow_page(), it will
use pte_offset_map_lock() to get the pte entry lock for the CONT-PTE size
hugetlb in follow_page_pte().  However this pte entry lock is incorrect
for the CONT-PTE size hugetlb, since we should use huge_pte_lock() to get
the correct lock, which is mm->page_table_lock.

That means the pte entry of the CONT-PTE size hugetlb under current pte
lock is unstable in follow_page_pte(), we can continue to migrate or
poison the pte entry of the CONT-PTE size hugetlb, which can cause some
potential race issues, even though they are under the 'pte lock'.

For example, suppose thread A is trying to look up a CONT-PTE size hugetlb
page by move_pages() syscall under the lock, however antoher thread B can
migrate the CONT-PTE hugetlb page at the same time, which will cause
thread A to get an incorrect page, if thread A also wants to do page
migration, then data inconsistency error occurs.

Moreover we have the same issue for CONT-PMD size hugetlb in
follow_huge_pmd().

To fix above issues, rename the follow_huge_pmd() as follow_huge_pmd_pte()
to handle PMD and PTE level size hugetlb, which uses huge_pte_lock() to
get the correct pte entry lock to make the pte entry stable.

Mike said:

Support for CONT_PMD/_PTE was added with bb9dd3df ("arm64: hugetlb:
refactor find_num_contig()").  Patch series "Support for contiguous pte
hugepages", v4.  However, I do not believe these code paths were
executed until migration support was added with 5480280d ("arm64/mm:
enable HugeTLB migration for contiguous bit HugeTLB pages") I would go
with 5480280d for the Fixes: targe.

Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.1662017562.git.baolin.wang@linux.alibaba.com


Fixes: 5480280d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
Signed-off-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Suggested-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
[5.4: Fixup contextual diffs before pin_user_pages()]
Signed-off-by: default avatarSamuel Mendoza-Jonas <samjonas@amazon.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 69d4f3ba

include/linux/hugetlb.h

+3 −3
Original line number Diff line number Diff line
@@ -127,8 +127,8 @@ struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address, 
struct page *follow_huge_pd(struct vm_area_struct *vma,

			    unsigned long address, hugepd_t hpd,

			    int flags, int pdshift);

struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,

				pmd_t *pmd, int flags);

struct page *follow_huge_pmd_pte(struct vm_area_struct *vma, unsigned long address,

				 int flags);

struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,

				pud_t *pud, int flags);

struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
@@ -175,7 +175,7 @@ static inline void hugetlb_show_meminfo(void) 
{

}

#define follow_huge_pd(vma, addr, hpd, flags, pdshift) NULL

#define follow_huge_pmd(mm, addr, pmd, flags)	NULL

#define follow_huge_pmd_pte(vma, addr, flags)	NULL

#define follow_huge_pud(mm, addr, pud, flags)	NULL

#define follow_huge_pgd(mm, addr, pgd, flags)	NULL

#define prepare_hugepage_range(file, addr, len)	(-EINVAL)

mm/gup.c

+12 −1
Original line number Diff line number Diff line
@@ -188,6 +188,17 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, 
	spinlock_t *ptl;

	pte_t *ptep, pte;



	/*

	 * Considering PTE level hugetlb, like continuous-PTE hugetlb on

	 * ARM64 architecture.

	 */

	if (is_vm_hugetlb_page(vma)) {

		page = follow_huge_pmd_pte(vma, address, flags);

		if (page)

			return page;

		return no_page_table(vma, flags);

	}



retry:

	if (unlikely(pmd_bad(*pmd)))

		return no_page_table(vma, flags);
@@ -333,7 +344,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, 
	if (pmd_none(pmdval))

		return no_page_table(vma, flags);

	if (pmd_huge(pmdval) && vma->vm_flags & VM_HUGETLB) {

		page = follow_huge_pmd(mm, address, pmd, flags);

		page = follow_huge_pmd_pte(vma, address, flags);

		if (page)

			return page;

		return no_page_table(vma, flags);

mm/hugetlb.c

+15 −15
Original line number Diff line number Diff line
@@ -5157,30 +5157,30 @@ follow_huge_pd(struct vm_area_struct *vma, 
}



struct page * __weak

follow_huge_pmd(struct mm_struct *mm, unsigned long address,

		pmd_t *pmd, int flags)

follow_huge_pmd_pte(struct vm_area_struct *vma, unsigned long address, int flags)

{

	struct hstate *h = hstate_vma(vma);

	struct mm_struct *mm = vma->vm_mm;

	struct page *page = NULL;

	spinlock_t *ptl;

	pte_t pte;

	pte_t *ptep, pte;



retry:

	ptl = pmd_lockptr(mm, pmd);

	spin_lock(ptl);

	/*

	 * make sure that the address range covered by this pmd is not

	 * unmapped from other threads.

	 */

	if (!pmd_huge(*pmd))

		goto out;

	pte = huge_ptep_get((pte_t *)pmd);

	ptep = huge_pte_offset(mm, address, huge_page_size(h));

	if (!ptep)

		return NULL;



	ptl = huge_pte_lock(h, mm, ptep);

	pte = huge_ptep_get(ptep);

	if (pte_present(pte)) {

		page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);

		page = pte_page(pte) +

			((address & ~huge_page_mask(h)) >> PAGE_SHIFT);

		if (flags & FOLL_GET)

			get_page(page);

	} else {

		if (is_hugetlb_entry_migration(pte)) {

			spin_unlock(ptl);

			__migration_entry_wait(mm, (pte_t *)pmd, ptl);

			__migration_entry_wait(mm, ptep, ptl);

			goto retry;

		}

		/*
@@ -5188,7 +5188,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, 
		 * follow_page_mask().

		 */

	}

out:



	spin_unlock(ptl);

	return page;

}