From: Andrea Arcangeli <aarca...@redhat.com> There are several cases write protection fault happens. It could be a write to zero page, swaped page or userfault write protected page. When the fault happens, there is no way to know if userfault write protect the page before. Here we just blindly issue a userfault notification for vma with VM_UFFD_WP regardless if app write protects it yet. Application should be ready to handle such wp fault.
In the swapin case, always swapin as readonly. This will cause false positive userfaults. We need to decide later if to eliminate them with a flag like soft-dirty in the swap entry (see _PAGE_SWP_SOFT_DIRTY). hugetlbfs wouldn't need to worry about swapouts but and tmpfs would be handled by a swap entry bit like anonymous memory. The main problem with no easy solution to eliminate the false positives, will be if/when userfaultfd is extended to real filesystem pagecache. When the pagecache is freed by reclaim we can't leave the radix tree pinned if the inode and in turn the radix tree is reclaimed as well. The estimation is that full accuracy and lack of false positives could be easily provided only to anonymous memory (as long as there's no fork or as long as MADV_DONTFORK is used on the userfaultfd anonymous range) tmpfs and hugetlbfs, it's most certainly worth to achieve it but in a later incremental patch. [pet...@redhat.com: don't conditionally drop FAULT_FLAG_WRITE in do_swap_page] Signed-off-by: Andrea Arcangeli <aarca...@redhat.com> Signed-off-by: Peter Xu <pet...@redhat.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Reviewed-by: Mike Rapoport <r...@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jgli...@redhat.com> Cc: Shaohua Li <s...@fb.com> Cc: Bobby Powers <bobbypow...@gmail.com> Cc: Brian Geffon <bgef...@google.com> Cc: David Hildenbrand <da...@redhat.com> Cc: Denis Plotnikov <dplotni...@virtuozzo.com> Cc: "Dr . David Alan Gilbert" <dgilb...@redhat.com> Cc: Hugh Dickins <hu...@google.com> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: "Kirill A . Shutemov" <kir...@shutemov.name> Cc: Martin Cracauer <craca...@cons.org> Cc: Marty McFadden <mcfadd...@llnl.gov> Cc: Maya Gokhale <gokha...@llnl.gov> Cc: Mel Gorman <mgor...@suse.de> Cc: Mike Kravetz <mike.krav...@oracle.com> Cc: Pavel Emelyanov <xe...@openvz.org> Cc: Rik van Riel <r...@redhat.com> Link: http://lkml.kernel.org/r/20200220163112.11409-3-pet...@redhat.com Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> https://jira.sw.ru/browse/PSBM-102938 (cherry picked from commit 529b930b87d997c3d231c9d8638a0bf8db569d70) Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- mm/memory.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 855d3109edd1..b261dec43bf4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2740,6 +2740,11 @@ static int do_wp_page(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; + if (userfaultfd_wp(vma)) { + pte_unmap_unlock(vmf->pte, vmf->ptl); + return handle_userfault(vmf, VM_UFFD_WP); + } + vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); if (!vmf->page) { /* @@ -3892,8 +3897,12 @@ static inline int create_huge_pmd(struct vm_fault *vmf) /* `inline' is required to avoid gcc 4.1.2 build error */ static inline int wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd) { - if (vma_is_anonymous(vmf->vma)) + if (vma_is_anonymous(vmf->vma)) { + if (userfaultfd_wp(vmf->vma)) + return handle_userfault(vmf, VM_UFFD_WP); return do_huge_pmd_wp_page(vmf, orig_pmd); + } + if (vmf->vma->vm_ops->huge_fault) return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD); -- 2.25.3 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
