s390: avoid cache aliasing under z/VM and KVM

commit 1f6b83e5e4d3 ("s390: avoid z13 cache aliasing") checks for the
machine type to optimize address space randomization and zero page
allocation to avoid cache aliases.

This check might fail under a hypervisor with migration support.
z/VMs "Single System Image and Live Guest Relocation" facility will
"fake" the machine type of the oldest system in the group. For example
in a group of zEC12 and Z13 the guest appears to run on a zEC12
(architecture fencing within the relocation domain)

Remove the machine type detection and always use cache aliasing
rules that are known to work for all machines. These are the z13
aliasing rules.

Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 27 deletions

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index c3c07d3505ba..c722400c7697 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -48,37 +48,13 @@ EXPORT_SYMBOL(zero_page_mask);
 
 static void __init setup_zero_pages(void)
 {
-	struct cpuid cpu_id;
 	unsigned int order;
 	struct page *page;
 	int i;
 
-	get_cpu_id(&cpu_id);
-	switch (cpu_id.machine) {
-	case 0x9672:	/* g5 */
-	case 0x2064:	/* z900 */
-	case 0x2066:	/* z900 */
-	case 0x2084:	/* z990 */
-	case 0x2086:	/* z990 */
-	case 0x2094:	/* z9-109 */
-	case 0x2096:	/* z9-109 */
-		order = 0;
-		break;
-	case 0x2097:	/* z10 */
-	case 0x2098:	/* z10 */
-	case 0x2817:	/* z196 */
-	case 0x2818:	/* z196 */
-		order = 2;
-		break;
-	case 0x2827:	/* zEC12 */
-	case 0x2828:	/* zEC12 */
-		order = 5;
-		break;
-	case 0x2964:	/* z13 */
-	default:
-		order = 7;
-		break;
-	}
+	/* Latest machines require a mapping granularity of 512KB */
+	order = 7;
+
 	/* Limit number of empty zero pages for small memory sizes */
 	while (order > 2 && (totalram_pages >> 10) < (1UL << order))
 		order--;