The patch titled
Subject: mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page
Date: Thu, 1 Sep 2022 18:41:31 +0800
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.
Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.1662017562.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/hugetlb.h | 8 ++++----
mm/gup.c | 14 +++++++++++++-
mm/hugetlb.c | 27 +++++++++++++--------------
3 files changed, 30 insertions(+), 19 deletions(-)
--- a/include/linux/hugetlb.h~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page
+++ a/include/linux/hugetlb.h
@@ -207,8 +207,8 @@ struct page *follow_huge_addr(struct mm_
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,
@@ -312,8 +312,8 @@ static inline struct page *follow_huge_p
return NULL;
}
-static inline struct page *follow_huge_pmd(struct mm_struct *mm,
- unsigned long address, pmd_t *pmd, int flags)
+static inline struct page *follow_huge_pmd_pte(struct vm_area_struct *vma,
+ unsigned long address, int flags)
{
return NULL;
}
--- a/mm/gup.c~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page
+++ a/mm/gup.c
@@ -530,6 +530,18 @@ static struct page *follow_page_pte(stru
if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
(FOLL_PIN | FOLL_GET)))
return ERR_PTR(-EINVAL);
+
+ /*
+ * 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);
@@ -662,7 +674,7 @@ static struct page *follow_pmd_mask(stru
if (pmd_none(pmdval))
return no_page_table(vma, flags);
if (pmd_huge(pmdval) && is_vm_hugetlb_page(vma)) {
- 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);
--- a/mm/hugetlb.c~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page
+++ a/mm/hugetlb.c
@@ -6944,12 +6944,13 @@ follow_huge_pd(struct vm_area_struct *vm
}
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;
/*
* FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via
@@ -6959,17 +6960,15 @@ follow_huge_pmd(struct mm_struct *mm, un
return NULL;
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);
/*
* try_grab_page() should always succeed here, because: a) we
* hold the pmd (ptl) lock, and b) we've just checked that the
@@ -6985,7 +6984,7 @@ retry:
} else {
if (is_hugetlb_entry_migration(pte)) {
spin_unlock(ptl);
- __migration_entry_wait_huge((pte_t *)pmd, ptl);
+ __migration_entry_wait_huge(ptep, ptl);
goto retry;
}
/*
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch
mm-migrate-do-not-retry-10-times-for-the-subpages-of-fail-to-migrate-thp.patch
mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch
mm-damon-replace-pmd_huge-with-pmd_trans_huge-for-thp.patch
