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authorAndrea Arcangeli <aarcange@redhat.com>2015-09-05 01:46:27 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-05 02:54:41 +0300
commitc1294d05de5df1ab8c93aa13c531782ede907e14 (patch)
treea9485ff9abe7fd118502fc84e05fbdeb8d668fbe /mm/huge_memory.c
parent19a809afe2fe089317226bbe5c5a1ce7f53dcdca (diff)
downloadlinux-c1294d05de5df1ab8c93aa13c531782ede907e14.tar.xz
userfaultfd: prevent khugepaged to merge if userfaultfd is armed
If userfaultfd is armed on a certain vma we can't "fill" the holes with zeroes or we'll break the userland on demand paging. The holes if the userfault is armed, are really missing information (not zeroes) that the userland has to load from network or elsewhere. The same issue happens for wrprotected ptes that we can't just convert into a single writable pmd_trans_huge. We could however in theory still merge across zeropages if only VM_UFFD_MISSING is set (so if VM_UFFD_WP is not set)... that could be slightly improved but it'd be much more complex code for a tiny corner case. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Pavel Emelyanov <xemul@parallels.com> Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com> Cc: zhang.zhanghailiang@huawei.com Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Andres Lagar-Cavilla <andreslc@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Hugh Dickins <hughd@google.com> Cc: Peter Feiner <pfeiner@google.com> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7735f99931fa..d38aaf9dcba6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2158,7 +2158,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out;
@@ -2611,7 +2612,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
- if (++none_or_zero <= khugepaged_max_ptes_none)
+ if (!userfaultfd_armed(vma) &&
+ ++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out_unmap;