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authorPeter Xu <peterx@redhat.com>2020-04-06 20:06:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-07 10:43:39 -0700
commite1e267c7928fe387e5e1cffeafb0de2d0473663a (patch)
tree56afcda13ad17fb3efbce5f35d78bd801006e76a /mm/khugepaged.c
parentf45ec5ff16a75f96dac8c89862d75f1d8739efd4 (diff)
khugepaged: skip collapse if uffd-wp detected
Don't collapse the huge PMD if there is any userfault write protected small PTEs. The problem is that the write protection is in small page granularity and there's no way to keep all these write protection information if the small pages are going to be merged into a huge PMD. The same thing needs to be considered for swap entries and migration entries. So do the check as well disregarding khugepaged_max_ptes_swap. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> 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: 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: Pavel Emelyanov <xemul@openvz.org> Cc: Rik van Riel <riel@redhat.com> Cc: Shaohua Li <shli@fb.com> Link: http://lkml.kernel.org/r/20200220163112.11409-12-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 3afc1e2d7a55..99d77ffb79c2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -29,6 +29,7 @@ enum scan_result {
SCAN_PMD_NULL,
SCAN_EXCEED_NONE_PTE,
SCAN_PTE_NON_PRESENT,
+ SCAN_PTE_UFFD_WP,
SCAN_PAGE_RO,
SCAN_LACK_REFERENCED_PAGE,
SCAN_PAGE_NULL,
@@ -1137,6 +1138,15 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
pte_t pteval = *_pte;
if (is_swap_pte(pteval)) {
if (++unmapped <= khugepaged_max_ptes_swap) {
+ /*
+ * Always be strict with uffd-wp
+ * enabled swap entries. Please see
+ * comment below for pte_uffd_wp().
+ */
+ if (pte_swp_uffd_wp(pteval)) {
+ result = SCAN_PTE_UFFD_WP;
+ goto out_unmap;
+ }
continue;
} else {
result = SCAN_EXCEED_SWAP_PTE;
@@ -1156,6 +1166,19 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
result = SCAN_PTE_NON_PRESENT;
goto out_unmap;
}
+ if (pte_uffd_wp(pteval)) {
+ /*
+ * Don't collapse the page if any of the small
+ * PTEs are armed with uffd write protection.
+ * Here we can also mark the new huge pmd as
+ * write protected if any of the small ones is
+ * marked but that could bring uknown
+ * userfault messages that falls outside of
+ * the registered range. So, just be simple.
+ */
+ result = SCAN_PTE_UFFD_WP;
+ goto out_unmap;
+ }
if (pte_write(pteval))
writable = true;