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    SubjectRe: [PATCH v2 2/3] mm/swapfile: Fix lost swap bits in unuse_pte()
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    On 2022/4/21 21:13, David Hildenbrand wrote:
    > On 21.04.22 14:53, Miaohe Lin wrote:
    >> This is observed by code review only but not any real report.
    >>
    >> When we turn off swapping we could have lost the bits stored in the swap
    >> ptes. The new rmap-exclusive bit is fine since that turned into a page
    >> flag, but not for soft-dirty and uffd-wp. Add them.
    >>
    >> Suggested-by: Peter Xu <peterx@redhat.com>
    >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
    >> ---
    >> mm/swapfile.c | 12 +++++++++---
    >> 1 file changed, 9 insertions(+), 3 deletions(-)
    >>
    >> diff --git a/mm/swapfile.c b/mm/swapfile.c
    >> index 95b63f69f388..332ccfc76142 100644
    >> --- a/mm/swapfile.c
    >> +++ b/mm/swapfile.c
    >> @@ -1783,7 +1783,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
    >> {
    >> struct page *swapcache;
    >> spinlock_t *ptl;
    >> - pte_t *pte;
    >> + pte_t *pte, new_pte;
    >> int ret = 1;
    >>
    >> swapcache = page;
    >> @@ -1832,8 +1832,14 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
    >> page_add_new_anon_rmap(page, vma, addr);
    >> lru_cache_add_inactive_or_unevictable(page, vma);
    >> }
    >> - set_pte_at(vma->vm_mm, addr, pte,
    >> - pte_mkold(mk_pte(page, vma->vm_page_prot)));
    >> + new_pte = pte_mkold(mk_pte(page, vma->vm_page_prot));
    >> + if (pte_swp_soft_dirty(*pte))
    >> + new_pte = pte_mksoft_dirty(new_pte);
    >> + if (pte_swp_uffd_wp(*pte)) {
    >> + new_pte = pte_mkuffd_wp(new_pte);
    >> + new_pte = pte_wrprotect(new_pte);
    >
    > The wrprotect shouldn't be necessary, we don't do a pte_mkwrite(). Note
    > that in do_swap_page() we might have done a
    > maybe_mkwrite(pte_mkdirty(pte)), which is why the pte_wrprotect() is
    > required there.

    You're so smart. I happened to be referring to the code in do_swap_page. ;)
    Now I see why pte_wrprotect() is only required there. Will remove it in the
    next verison when there is enough feedback. Many thanks!

    >

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