[PATCH mm-unstable v1 07/20] mm: don't call vm_ops->huge_fault() in wp_huge_pmd()/wp_huge_pud() for

David Hildenbrand
2022-11-16T10:26:46Z

If we already have a PMD/PUD mapped write-protected in a private mapping
and we want to break COW either due to FAULT_FLAG_WRITE or
FAULT_FLAG_UNSHARE, there is no need to inform the file system just like on
the PTE path.

Let's just split (->zap) + fallback in that case.

This is a preparation for more generic FAULT_FLAG_UNSHARE support in
COW mappings.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/memory.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c35e6cd32b6a..d47ad33c6487 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4802,6 +4802,7 @@ static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
{
const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
+ vm_fault_t ret;

if (vma_is_anonymous(vmf->vma)) {
if (likely(!unshare) &&
@@ -4809,11 +4810,13 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
return handle_userfault(vmf, VM_UFFD_WP);
return do_huge_pmd_wp_page(vmf);
}
- if (vmf->vma->vm_ops->huge_fault) {
- vm_fault_t ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);

- if (!(ret & VM_FAULT_FALLBACK))
- return ret;
+ if (vmf->vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
+ if (vmf->vma->vm_ops->huge_fault) {
+ ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);
+ if (!(ret & VM_FAULT_FALLBACK))
+ return ret;
+ }
}

/* COW or write-notify handled on pte level: split pmd. */
@@ -4839,14 +4842,17 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
{
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+ vm_fault_t ret;
+
/* No support for anonymous transparent PUD pages yet */
if (vma_is_anonymous(vmf->vma))
goto split;
- if (vmf->vma->vm_ops->huge_fault) {
- vm_fault_t ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD);
-
- if (!(ret & VM_FAULT_FALLBACK))
- return ret;
+ if (vmf->vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
+ if (vmf->vma->vm_ops->huge_fault) {
+ ret = vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD);
+ if (!(ret & VM_FAULT_FALLBACK))
+ return ret;
+ }
}
split:
/* COW or write-notify not handled on PUD level: split pud.*/
--
2.38.1