From 2faee8ff9dc6f4bfe46f6d2d110add858140fb20 Mon Sep 17 00:00:00 2001 From: Dominik Dingel Date: Thu, 23 Oct 2014 12:08:38 +0200 Subject: s390/mm: prevent and break zero page mappings in case of storage keys As soon as storage keys are enabled we need to stop working on zero page mappings to prevent inconsistencies between storage keys and pgste. Otherwise following data corruption could happen: 1) guest enables storage key 2) guest sets storage key for not mapped page X -> change goes to PGSTE 3) guest reads from page X -> as X was not dirty before, the page will be zero page backed, storage key from PGSTE for X will go to storage key for zero page 4) guest sets storage key for not mapped page Y (same logic as above 5) guest reads from page Y -> as Y was not dirty before, the page will be zero page backed, storage key from PGSTE for Y will got to storage key for zero page overwriting storage key for X While holding the mmap sem, we are safe against changes on entries we already fixed, as every fault would need to take the mmap_sem (read). Other vCPUs executing storage key instructions will get a one time interception and be serialized also with mmap_sem. Signed-off-by: Dominik Dingel Reviewed-by: Paolo Bonzini Signed-off-by: Martin Schwidefsky --- arch/s390/include/asm/pgtable.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/s390/include') diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h index 4399be1aaeff..df2e7f14ffb7 100644 --- a/arch/s390/include/asm/pgtable.h +++ b/arch/s390/include/asm/pgtable.h @@ -479,6 +479,11 @@ static inline int mm_has_pgste(struct mm_struct *mm) return 0; } +/* + * In the case that a guest uses storage keys + * faults should no longer be backed by zero pages + */ +#define mm_forbids_zeropage mm_use_skey static inline int mm_use_skey(struct mm_struct *mm) { #ifdef CONFIG_PGSTE -- cgit v1.2.3