Commit c56d1b62 authored by Peter Xu's avatar Peter Xu Committed by Andrew Morton

mm/shmem: handle uffd-wp during fork()

Normally we skip copy page when fork() for VM_SHARED shmem, but we can't
skip it anymore if uffd-wp is enabled on dst vma.  This should only happen
when the src uffd has UFFD_FEATURE_EVENT_FORK enabled on uffd-wp shmem
vma, so that VM_UFFD_WP will be propagated onto dst vma too, then we
should copy the pgtables with uffd-wp bit and pte markers, because these
information will be lost otherwise.

Since the condition checks will become even more complicated for deciding
"whether a vma needs to copy the pgtable during fork()", introduce a
helper vma_needs_copy() for it, so everything will be clearer.

Link: https://lkml.kernel.org/r/20220405014855.14468-1-peterx@redhat.comSigned-off-by: default avatarPeter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 019c2d8b
...@@ -867,6 +867,14 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, ...@@ -867,6 +867,14 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
if (try_restore_exclusive_pte(src_pte, src_vma, addr)) if (try_restore_exclusive_pte(src_pte, src_vma, addr))
return -EBUSY; return -EBUSY;
return -ENOENT; return -ENOENT;
} else if (is_pte_marker_entry(entry)) {
/*
* We're copying the pgtable should only because dst_vma has
* uffd-wp enabled, do sanity check.
*/
WARN_ON_ONCE(!userfaultfd_wp(dst_vma));
set_pte_at(dst_mm, addr, dst_pte, pte);
return 0;
} }
if (!userfaultfd_wp(dst_vma)) if (!userfaultfd_wp(dst_vma))
pte = pte_swp_clear_uffd_wp(pte); pte = pte_swp_clear_uffd_wp(pte);
...@@ -1221,6 +1229,38 @@ copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, ...@@ -1221,6 +1229,38 @@ copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
return 0; return 0;
} }
/*
* Return true if the vma needs to copy the pgtable during this fork(). Return
* false when we can speed up fork() by allowing lazy page faults later until
* when the child accesses the memory range.
*/
bool
vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
{
/*
* Always copy pgtables when dst_vma has uffd-wp enabled even if it's
* file-backed (e.g. shmem). Because when uffd-wp is enabled, pgtable
* contains uffd-wp protection information, that's something we can't
* retrieve from page cache, and skip copying will lose those info.
*/
if (userfaultfd_wp(dst_vma))
return true;
if (src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP))
return true;
if (src_vma->anon_vma)
return true;
/*
* Don't copy ptes where a page fault will fill them correctly. Fork
* becomes much lighter when there are big shared or private readonly
* mappings. The tradeoff is that copy_page_range is more efficient
* than faulting.
*/
return false;
}
int int
copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
{ {
...@@ -1234,14 +1274,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) ...@@ -1234,14 +1274,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
bool is_cow; bool is_cow;
int ret; int ret;
/* if (!vma_needs_copy(dst_vma, src_vma))
* Don't copy ptes where a page fault will fill them correctly.
* Fork becomes much lighter when there are big shared or private
* readonly mappings. The tradeoff is that copy_page_range is more
* efficient than faulting.
*/
if (!(src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) &&
!src_vma->anon_vma)
return 0; return 0;
if (is_vm_hugetlb_page(src_vma)) if (is_vm_hugetlb_page(src_vma))
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment