mm: introduce mm_forbids_zeropage function

Add a new function stub to allow architectures to disable for
an mm_structthe backing of non-present, anonymous pages with
read-only empty zero pages.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 74c78aa8bc2f..7e9c15cb93a9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -805,7 +805,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 return VM_FAULT_OOM;
         if (unlikely(khugepaged_enter(vma)))
                 return VM_FAULT_OOM;
-        if (!(flags & FAULT_FLAG_WRITE) &&
+        if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
                         transparent_hugepage_use_zero_page()) {
                 spinlock_t *ptl;
                 pgtable_t pgtable;
diff --git a/mm/memory.c b/mm/memory.c
index 1cc6bfbd872e..d722d4f481c9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2640,7 +2640,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 return VM_FAULT_SIGBUS;
 
         /* Use the zero-page for reads */
-        if (!(flags & FAULT_FLAG_WRITE)) {
+        if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) {
                 entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
                                                 vma->vm_page_prot));
                 page_table = pte_offset_map_lock(mm, pmd, address, &ptl);