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>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 27eb1bf..ab7dadc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -56,6 +56,17 @@
#define __pa_symbol(x) __pa(RELOC_HIDE((unsigned long)(x), 0))
#endif
+/*
+ * To prevent common memory management code establishing
+ * a zero page mapping on a read fault.
+ * This macro should be defined within <asm/pgtable.h>.
+ * s390 does this to prevent multiplexing of hardware bits
+ * related to the physical page in case of virtualization.
+ */
+#ifndef mm_forbids_zeropage
+#define mm_forbids_zeropage(X) (0)
+#endif
+
extern unsigned long sysctl_user_reserve_kbytes;
extern unsigned long sysctl_admin_reserve_kbytes;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 74c78aa..7e9c15c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -805,7 +805,7 @@
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 1cc6bfb..d722d4f4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2640,7 +2640,7 @@
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);