s390/mm,kvm: fix software dirty bits vs. kvm for old machines

For machines without enhanced supression on protection the software
dirty bit code forces the pte dirty bit and clears the page protection
bit in pgste_set_pte. This is done for all pte types, the check for
present ptes is missing. As a result swap ptes and other not-present
ptes can get corrupted.
Add a check for the _PAGE_PRESENT bit to pgste_set_pte before modifying
the pte value.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 9b60a36c348d5422dc325463bcb26efeee64161d..2204400d0bd58d4a1e45c82394ff5cbd100aa2cc 100644 (file)
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -748,7 +748,9 @@ static inline void pgste_set_key(pte_t *ptep, pgste_t pgste, pte_t entry)
 
 static inline void pgste_set_pte(pte_t *ptep, pte_t entry)
 {
-       if (!MACHINE_HAS_ESOP && (pte_val(entry) & _PAGE_WRITE)) {
+       if (!MACHINE_HAS_ESOP &&
+           (pte_val(entry) & _PAGE_PRESENT) &&
+           (pte_val(entry) & _PAGE_WRITE)) {
                /*
                 * Without enhanced suppression-on-protection force
                 * the dirty bit on for all writable ptes.