userfaultfd: wp: support swap and page migration
For either swap and page migration, we all use the bit 2 of the entry to
identify whether this entry is uffd write-protected. It plays a similar
role as the existing soft dirty bit in swap entries but only for keeping
the uffd-wp tracking for a specific PTE/PMD.
Something special here is that when we want to recover the uffd-wp bit
from a swap/migration entry to the PTE bit we'll also need to take care of
the _PAGE_RW bit and make sure it's cleared, otherwise even with the
_PAGE_UFFD_WP bit we can't trap it at all.
In change_pte_range() we do nothing for uffd if the PTE is a swap entry.
That can lead to data mismatch if the page that we are going to write
protect is swapped out when sending the UFFDIO_WRITEPROTECT. This patch
also applies/removes the uffd-wp bit even for the swap entries.
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-11-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/migrate.c b/mm/migrate.c
index c1412e0..7160c15 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -243,11 +243,15 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
entry = pte_to_swp_entry(*pvmw.pte);
if (is_write_migration_entry(entry))
pte = maybe_mkwrite(pte, vma);
+ else if (pte_swp_uffd_wp(*pvmw.pte))
+ pte = pte_mkuffd_wp(pte);
if (unlikely(is_zone_device_page(new))) {
if (is_device_private_page(new)) {
entry = make_device_private_entry(new, pte_write(pte));
pte = swp_entry_to_pte(entry);
+ if (pte_swp_uffd_wp(*pvmw.pte))
+ pte = pte_mkuffd_wp(pte);
}
}
@@ -2338,6 +2342,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pte))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (pte_uffd_wp(pte))
+ swp_pte = pte_swp_mkuffd_wp(swp_pte);
set_pte_at(mm, addr, ptep, swp_pte);
/*