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mm/shmem: allows file-back mem to be uffd wr-protected on thps 

We don't have "huge" version of pte markers, instead when necessary we
split the thp.

However split the thp is not enough, because file-backed thp is handled
totally differently comparing to anonymous thps: rather than doing a real
split, the thp pmd will simply got cleared in __split_huge_pmd_locked().

That is not enough if e.g.  when there is a thp covers range [0, 2M) but
we want to wr-protect small page resides in [4K, 8K) range, because after
__split_huge_pmd() returns, there will be a none pmd, and
change_pmd_range() will just skip it right after the split.

Here we leverage the previously introduced change_pmd_prepare() macro so
that we'll populate the pmd with a pgtable page after the pmd split (in
which process the pmd will be cleared for cases like shmem).  Then
change_pte_range() will do all the rest for us by installing the uffd-wp
pte marker at any none pte that we'd like to wr-protect.

Link: https://lkml.kernel.org/r/20220405014852.14413-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.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 Kravetz <mike.kravetz@oracle.com>
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 20:22:53 -07:00 committed by Andrew Morton
parent fe2567eb55
commit 019c2d8b95
1 changed files with 8 additions and 1 deletions
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9
mm/mprotect.c
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@ -338,8 +338,15 @@ static inline unsigned long change_pmd_range(struct mmu_gather *tlb,
}
if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
if ((next - addr != HPAGE_PMD_SIZE) ||
uffd_wp_protect_file(vma, cp_flags)) {
__split_huge_pmd(vma, pmd, addr, false, NULL);
/*
* For file-backed, the pmd could have been
* cleared; make sure pmd populated if
* necessary, then fall-through to pte level.
*/
change_pmd_prepare(vma, pmd, cp_flags);
} else {
/*
* change_huge_pmd() does not defer TLB flushes,