Re: [PATCH v1 08/12] s390x/mmu_helper: avoid setting the storage key if nothing changed

[Thomas Huth <thuth@redhat.com>]

On 05/08/2021 17.28, David Hildenbrand wrote:
> Avoid setting the key if nothing changed.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   target/s390x/mmu_helper.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/target/s390x/mmu_helper.c b/target/s390x/mmu_helper.c
> index 36ab4e9c81..0c2c39a970 100644
> --- a/target/s390x/mmu_helper.c
> +++ b/target/s390x/mmu_helper.c
> @@ -301,7 +301,7 @@ static void mmu_handle_skey(target_ulong addr, int rw, int *flags)
>   {
>       static S390SKeysClass *skeyclass;
>       static S390SKeysState *ss;
> -    uint8_t key;
> +    uint8_t key, old_key;
>       int rc;
>   
>       /*
> @@ -337,6 +337,7 @@ static void mmu_handle_skey(target_ulong addr, int rw, int *flags)
>           trace_get_skeys_nonzero(rc);
>           return;
>       }
> +    old_key = key;
>   
>       switch (rw) {
>       case MMU_DATA_LOAD:
> @@ -360,9 +361,11 @@ static void mmu_handle_skey(target_ulong addr, int rw, int *flags)
>       /* Any store/fetch sets the reference bit */
>       key |= SK_R;
>   
> -    rc = skeyclass->set_skeys(ss, addr / TARGET_PAGE_SIZE, 1, &key);
> -    if (rc) {
> -        trace_set_skeys_nonzero(rc);
> +    if (key != old_key) {
> +        rc = skeyclass->set_skeys(ss, addr / TARGET_PAGE_SIZE, 1, &key);
> +        if (rc) {
> +            trace_set_skeys_nonzero(rc);
> +        }
>       }
>   }
>   
> 

Reviewed-by: Thomas Huth <thuth@redhat.com>