Commit 44f86392 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/hugetlb: fix uffd-wp handling for migration entries in hugetlb_change_protection() 

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

Link: https://lkml.kernel.org/r/20221222205511.675832-3-david@redhat.com


Fixes: 60dfaad6 ("mm/hugetlb: allow uffd wr-protect none ptes")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 0e678153

mm/hugetlb.c

+9 −8
Original line number Diff line number Diff line
@@ -6662,10 +6662,9 @@ 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));
@@ -6673,13 +6672,15 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, 
					entry = make_readable_migration_entry(

								swp_offset(entry));

				newpte = swp_entry_to_pte(entry);

				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);

				pages++;

			}

		} else if (unlikely(is_pte_marker(pte))) {

			/* No other markers apply for now. */

			WARN_ON_ONCE(!pte_marker_uffd_wp(pte));