Commit 24bf08c4 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/userfaultfd: fix uffd-wp handling for THP migration entries 

Looks like what we fixed for hugetlb in commit 44f86392 ("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: f45ec5ff ("userfaultfd: wp: support swap and page migration")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 998ad18b

mm/huge_memory.c

+12 −2
Original line number Diff line number Diff line
@@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, 
	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 *tlb, struct vm_area_struct *vma, 
				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_vma_mapped_walk *pvmw, 
	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);