[PATCH RFC 07/19] mm: don't call vm_ops->huge_fault() in wp_huge_pmd()/wp_huge_pud() for private mappings

[David Hildenbrand]

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 <da...@redhat.com>
---
 mm/memory.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 41e4c697033a..d2f9673755be 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4791,6 +4791,7 @@ 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) &&
@@ -4798,11 +4799,13 @@ 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. */
@@ -4828,14 +4831,17 @@ 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