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;