[S390] fix page change underindication in pgste_update_all

This patch makes sure we don't underindicate _PAGE_CHANGED in case
we have a race between an operation that changes the page and this
code path that hits us between page_get_storage_key and
page_set_storage_key. Note that we still have a potential
underindication on _PAGE_REFERENCED in the unlikely event that
the page was changed but not referenced _and_ someone references
the page in the race window. That's not considered to be a problem.

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

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 524d23b8610c..4f289ff0b7fe 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -599,10 +599,10 @@ static inline pgste_t pgste_update_all(pte_t *ptep, pgste_t pgste)
         skey = page_get_storage_key(address);
         bits = skey & (_PAGE_CHANGED | _PAGE_REFERENCED);
         /* Clear page changed & referenced bit in the storage key */
-        if (bits) {
-                skey ^= bits;
-                page_set_storage_key(address, skey, 1);
-        }
+        if (bits & _PAGE_CHANGED)
+                page_set_storage_key(address, skey ^ bits, 1);
+        else if (bits)
+                page_reset_referenced(address);
         /* Transfer page changed & referenced bit to guest bits in pgste */
         pgste_val(pgste) |= bits << 48;         /* RCP_GR_BIT & RCP_GC_BIT */
         /* Get host changed & referenced bits from pgste */