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authorPeter Xu <peterx@redhat.com>2023-04-05 18:51:20 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-04-16 20:41:24 +0300
commitdd47ac428c3f5f3bcabe845f36be870fe6c20784 (patch)
tree412deac482b952dbfe44bf7a5b4715a401e5c23c /mm/khugepaged.c
parent24bf08c4376be417f16ceb609188b16f461b0443 (diff)
downloadlinux-dd47ac428c3f5f3bcabe845f36be870fe6c20784.tar.xz
mm/khugepaged: check again on anon uffd-wp during isolation
Khugepaged collapse an anonymous thp in two rounds of scans. The 2nd round done in __collapse_huge_page_isolate() after hpage_collapse_scan_pmd(), during which all the locks will be released temporarily. It means the pgtable can change during this phase before 2nd round starts. It's logically possible some ptes got wr-protected during this phase, and we can errornously collapse a thp without noticing some ptes are wr-protected by userfault. e1e267c7928f wanted to avoid it but it only did that for the 1st phase, not the 2nd phase. Since __collapse_huge_page_isolate() happens after a round of small page swapins, we don't need to worry on any !present ptes - if it existed khugepaged will already bail out. So we only need to check present ptes with uffd-wp bit set there. This is something I found only but never had a reproducer, I thought it was one caused a bug in Muhammad's recent pagemap new ioctl work, but it turns out it's not the cause of that but an userspace bug. However this seems to still be a real bug even with a very small race window, still worth to have it fixed and copy stable. Link: https://lkml.kernel.org/r/20230405155120.3608140-1-peterx@redhat.com Fixes: e1e267c7928f ("khugepaged: skip collapse if uffd-wp detected") Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Yang Shi <shy828301@gmail.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/khugepaged.c')
-rw-r--r--mm/khugepaged.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 92e6f56a932d..0ec69b96b497 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -572,6 +572,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
result = SCAN_PTE_NON_PRESENT;
goto out;
}
+ if (pte_uffd_wp(pteval)) {
+ result = SCAN_PTE_UFFD_WP;
+ goto out;
+ }
page = vm_normal_page(vma, address, pteval);
if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
result = SCAN_PAGE_NULL;