We have to update the uffd-wp SWP PTE bit independent of the type of migration entry. Currently, if we're unlucky and we want to install/clear the uffd-wp bit just while we're migrating a read-only mapped hugetlb page, we would miss to set/clear the uffd-wp bit.
Further, if we're processing a readable-exclusive migration entry and neither want to set or clear the uffd-wp bit, we could currently end up losing the uffd-wp bit. Note that the same would hold for writable migrating entries, however, having a writable migration entry with the uffd-wp bit set would already mean that something went wrong.
Note that the change from !is_readable_migration_entry -> writable_migration_entry is harmless and actually cleaner, as raised by Miaohe Lin and discussed in [1].
[1] https://lkml.kernel.org/r/90dd6a93-4500-e0de-2bf0-bf522c311b0c@huawei.com
Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Cc: stable@vger.kernel.org Signed-off-by: David Hildenbrand david@redhat.com --- mm/hugetlb.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 3a94f519304f..9552a6d1a281 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6516,10 +6516,9 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, } else if (unlikely(is_hugetlb_entry_migration(pte))) { swp_entry_t entry = pte_to_swp_entry(pte); struct page *page = pfn_swap_entry_to_page(entry); + pte_t newpte = pte;
- if (!is_readable_migration_entry(entry)) { - pte_t newpte; - + if (is_writable_migration_entry(entry)) { if (PageAnon(page)) entry = make_readable_exclusive_migration_entry( swp_offset(entry)); @@ -6527,13 +6526,15 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, entry = make_readable_migration_entry( swp_offset(entry)); newpte = swp_entry_to_pte(entry); - if (uffd_wp) - newpte = pte_swp_mkuffd_wp(newpte); - else if (uffd_wp_resolve) - newpte = pte_swp_clear_uffd_wp(newpte); - set_huge_pte_at(mm, address, ptep, newpte); pages++; } + + if (uffd_wp) + newpte = pte_swp_mkuffd_wp(newpte); + else if (uffd_wp_resolve) + newpte = pte_swp_clear_uffd_wp(newpte); + if (!pte_same(pte, newpte)) + set_huge_pte_at(mm, address, ptep, newpte); } else if (unlikely(is_pte_marker(pte))) { /* No other markers apply for now. */ WARN_ON_ONCE(!pte_marker_uffd_wp(pte));