Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path was overlooked.
Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to find the huge ptep. It's possible that huge_pte_alloc() can fail with high memory pressure, in that case stop the loop immediately and fail silently. This is not the most ideal solution but it matches with what we do with shmem meanwhile it avoids the splat in dmesg.
Cc: linux-stable stable@vger.kernel.org # 5.19+ Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Reported-by: James Houghton jthoughton@google.com Signed-off-by: Peter Xu peterx@redhat.com --- mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bf7a1f628357..017d9159cddf 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6649,8 +6649,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, spinlock_t *ptl; ptep = hugetlb_walk(vma, address, psize); if (!ptep) { - address |= last_addr_mask; - continue; + if (!uffd_wp) { + address |= last_addr_mask; + continue; + } + /* + * Userfaultfd wr-protect requires pgtable + * pre-allocations to install pte markers. + */ + ptep = huge_pte_alloc(mm, vma, address, psize); + if (!ptep) + break; } ptl = huge_pte_lock(h, mm, ptep); if (huge_pmd_unshare(mm, vma, address, ptep)) {
On Wed, Jan 4, 2023 at 10:52 PM Peter Xu peterx@redhat.com wrote:
Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path was overlooked.
Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to find the huge ptep. It's possible that huge_pte_alloc() can fail with high memory pressure, in that case stop the loop immediately and fail silently. This is not the most ideal solution but it matches with what we do with shmem meanwhile it avoids the splat in dmesg.
Cc: linux-stable stable@vger.kernel.org # 5.19+ Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Reported-by: James Houghton jthoughton@google.com Signed-off-by: Peter Xu peterx@redhat.com
mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
Acked-by: James Houghton jthoughton@google.com
On 04.01.23 23:52, Peter Xu wrote:
Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path was overlooked.
Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to find the huge ptep. It's possible that huge_pte_alloc() can fail with high memory pressure, in that case stop the loop immediately and fail silently. This is not the most ideal solution but it matches with what we do with shmem meanwhile it avoids the splat in dmesg.
Cc: linux-stable stable@vger.kernel.org # 5.19+ Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Reported-by: James Houghton jthoughton@google.com Signed-off-by: Peter Xu peterx@redhat.com
mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bf7a1f628357..017d9159cddf 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6649,8 +6649,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, spinlock_t *ptl; ptep = hugetlb_walk(vma, address, psize);
if (!ptep && likely(!uffd_wp)) { /* Nothing to protect. */ address |= last_addr_mask; continue; } else if (!ptep) { ... }
Might look slightly more readable would minimize changes. This should work, so
Acked-by: David Hildenbrand david@redhat.com
if (!ptep) {
address |= last_addr_mask;continue;
if (!uffd_wp) {address |= last_addr_mask;continue;}/** Userfaultfd wr-protect requires pgtable* pre-allocations to install pte markers.*/ptep = huge_pte_alloc(mm, vma, address, psize);if (!ptep)break;
On 01/04/23 17:52, Peter Xu wrote:
Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path was overlooked.
Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to find the huge ptep. It's possible that huge_pte_alloc() can fail with high memory pressure, in that case stop the loop immediately and fail silently. This is not the most ideal solution but it matches with what we do with shmem meanwhile it avoids the splat in dmesg.
Cc: linux-stable stable@vger.kernel.org # 5.19+ Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Reported-by: James Houghton jthoughton@google.com Signed-off-by: Peter Xu peterx@redhat.com
mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
Thanks Peter and James!
Reviewed-by: Mike Kravetz mike.kravetz@oracle.com
linux-stable-mirror@lists.linaro.org
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David Hildenbrand -
James Houghton -
Mike Kravetz -
Peter Xu