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mm/hugetlb: only drop uffd-wp special pte if required

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As with shmem uffd-wp special ptes, only drop the uffd-wp special swap pte
if unmapping an entire vma or synchronized such that faults can not race
with the unmap operation.  This requires passing zap_flags all the way to
the lowest level hugetlb unmap routine: __unmap_hugepage_range.

In general, unmap calls originated in hugetlbfs code will pass the
ZAP_FLAG_DROP_MARKER flag as synchronization is in place to prevent
faults.  The exception is hole punch which will first unmap without any
synchronization.  Later when hole punch actually removes the page from the
file, it will check to see if there was a subsequent fault and if so take
the hugetlb fault mutex while unmapping again.  This second unmap will
pass in ZAP_FLAG_DROP_MARKER.

The justification of "whether to apply ZAP_FLAG_DROP_MARKER flag when
unmap a hugetlb range" is (IMHO): we should never reach a state when a
page fault could errornously fault in a page-cache page that was
wr-protected to be writable, even in an extremely short period.  That
could happen if e.g.  we pass ZAP_FLAG_DROP_MARKER when
hugetlbfs_punch_hole() calls hugetlb_vmdelete_list(), because if a page
faults after that call and before remove_inode_hugepages() is executed,
the page cache can be mapped writable again in the small racy window, that
can cause unexpected data overwritten.

[peterx@redhat.com: fix sparse warning]
  Link: https://lkml.kernel.org/r/Ylcdw8I1L5iAoWhb@xz-m1.local
[akpm@linux-foundation.org: move zap_flags_t from mm.h to mm_types.h to fix build issues]
Link: https://lkml.kernel.org/r/20220405014915.14873-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Xu 2022-05-12 20:22:55 -07:00 • committed by Andrew Morton
parent 60dfaad65a
commit 05e90bd05e
6 changed files with 45 additions and 20 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/linux/hugetlb.h
View file

@ -143,11 +143,12 @@ long follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *,
unsigned long *, unsigned long *, long, unsigned int,
int *);
void unmap_hugepage_range(struct vm_area_struct *,
unsigned long, unsigned long, struct page *);
unsigned long, unsigned long, struct page *,
zap_flags_t);
void __unmap_hugepage_range_final(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long start, unsigned long end,
struct page *ref_page);
struct page *ref_page, zap_flags_t zap_flags);
void hugetlb_report_meminfo(struct seq_file *);
int hugetlb_report_node_meminfo(char *buf, int len, int nid);
void hugetlb_show_meminfo(void);
@ -406,7 +407,8 @@ static inline unsigned long hugetlb_change_protection(
static inline void __unmap_hugepage_range_final(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start,
unsigned long end, struct page *ref_page)
unsigned long end, struct page *ref_page,
zap_flags_t zap_flags)
{
BUG();
}