The patch titled Subject: mm/userfaultfd: fix uffd-wp handling for THP migration entries has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: David Hildenbrand david@redhat.com Subject: mm/userfaultfd: fix uffd-wp handling for THP migration entries Date: Wed, 5 Apr 2023 18:02:35 +0200
Looks like what we fixed for hugetlb in commit 44f86392bdd1 ("mm/hugetlb: fix uffd-wp handling for migration entries in hugetlb_change_protection()") similarly applies to THP.
Setting/clearing uffd-wp on THP migration entries is not implemented properly. Further, while removing migration PMDs considers the uffd-wp bit, inserting migration PMDs does not consider the uffd-wp bit.
We have to set/clear independently of the migration entry type in change_huge_pmd() and properly copy the uffd-wp bit in set_pmd_migration_entry().
Verified using a simple reproducer that triggers migration of a THP, that the set_pmd_migration_entry() no longer loses the uffd-wp bit.
Link: https://lkml.kernel.org/r/20230405160236.587705-2-david@redhat.com Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration") Signed-off-by: David Hildenbrand david@redhat.com Reviewed-by: Peter Xu peterx@redhat.com Cc: stable@vger.kernel.org Cc: Muhammad Usama Anjum usama.anjum@collabora.com Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/huge_memory.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
--- a/mm/huge_memory.c~mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries +++ a/mm/huge_memory.c @@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *t if (is_swap_pmd(*pmd)) { swp_entry_t entry = pmd_to_swp_entry(*pmd); struct page *page = pfn_swap_entry_to_page(entry); + pmd_t newpmd;
VM_BUG_ON(!is_pmd_migration_entry(*pmd)); if (is_writable_migration_entry(entry)) { - pmd_t newpmd; /* * A protection check is difficult so * just be safe and disable write @@ -1855,8 +1855,16 @@ int change_huge_pmd(struct mmu_gather *t newpmd = pmd_swp_mksoft_dirty(newpmd); if (pmd_swp_uffd_wp(*pmd)) newpmd = pmd_swp_mkuffd_wp(newpmd); - set_pmd_at(mm, addr, pmd, newpmd); + } else { + newpmd = *pmd; } + + if (uffd_wp) + newpmd = pmd_swp_mkuffd_wp(newpmd); + else if (uffd_wp_resolve) + newpmd = pmd_swp_clear_uffd_wp(newpmd); + if (!pmd_same(*pmd, newpmd)) + set_pmd_at(mm, addr, pmd, newpmd); goto unlock; } #endif @@ -3251,6 +3259,8 @@ int set_pmd_migration_entry(struct page_ pmdswp = swp_entry_to_pmd(entry); if (pmd_soft_dirty(pmdval)) pmdswp = pmd_swp_mksoft_dirty(pmdswp); + if (pmd_uffd_wp(pmdval)) + pmdswp = pmd_swp_mkuffd_wp(pmdswp); set_pmd_at(mm, address, pvmw->pmd, pmdswp); page_remove_rmap(page, vma, true); put_page(page); _
Patches currently in -mm which might be from david@redhat.com are
mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch m68k-mm-use-correct-bit-number-in-_page_swp_exclusive-comment.patch mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.patch