This is a note to let you know that I've just added the patch titled
mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From fac35ba763ed07ba93154c95ffc0c4a55023707f Mon Sep 17 00:00:00 2001
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Date: Thu, 1 Sep 2022 18:41:31 +0800
Subject: mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
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 bb9dd3df8ee9 ("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 5480280d3f2d ("arm64/mm:
enable HugeTLB migration for contiguous bit HugeTLB pages") I would go
with 5480280d3f2d for the Fixes: targe.
Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.1662017562.git.baolin.wang@xxxxxxxxxxxxxxxxx
Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-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>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
[5.4: Fixup contextual diffs before pin_user_pages()]
Signed-off-by: Samuel Mendoza-Jonas <samjonas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/hugetlb.h | 6 +++---
mm/gup.c | 13 ++++++++++++-
mm/hugetlb.c | 30 +++++++++++++++---------------
3 files changed, 30 insertions(+), 19 deletions(-)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -127,8 +127,8 @@ 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,
@@ -175,7 +175,7 @@ static inline void hugetlb_show_meminfo(
{
}
#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)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -188,6 +188,17 @@ static struct page *follow_page_pte(stru
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(stru
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);
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5157,30 +5157,30 @@ 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;
+
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 @@ retry:
* follow_page_mask().
*/
}
-out:
+
spin_unlock(ptl);
return page;
}
Patches currently in stable-queue which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
queue-5.4/mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch
