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

Martin Schwidefsky · Martin Schwidefsky · commit af0ebc40a81c · 2013-10-15T13:47:57.000+02:00
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 &lt;schwidefsky@de.ibm.com&gt;
diff --git 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.
