mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page

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@linux.alibaba.com
Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Mike 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: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3ec981a0d8b3..67c88b82fc32 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -207,8 +207,8 @@ 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,
@@ -312,8 +312,8 @@ static inline struct page *follow_huge_pd(struct vm_area_struct *vma,
 	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;
 }