[PATCH for-8.0] target/s390x/tcg/mem_helper: Test the right bits in psw_key_valid()

[PATCH for-8.0] target/s390x/tcg/mem_helper: Test the right bits in psw_key_valid()

[Thomas Huth]

The PSW key mask is a 16 bit field, and the psw_key variable is
in the range from 0 to 15, so it does not make sense to use
"0x80 >> psw_key" for testing the bits here. We should use 0x8000
instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 Found by code inspection (Linux likely does not use these PSW key masks
 yet, otherwise we might have noticed earlier)

 target/s390x/tcg/mem_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
index 9542fad59b..cb82cd1c1d 100644
--- a/target/s390x/tcg/mem_helper.c
+++ b/target/s390x/tcg/mem_helper.c
@@ -51,7 +51,7 @@ static inline bool psw_key_valid(CPUS390XState *env, uint8_t psw_key)
 
     if (env->psw.mask & PSW_MASK_PSTATE) {
         /* PSW key has range 0..15, it is valid if the bit is 1 in the PKM */
-        return pkm & (0x80 >> psw_key);
+        return pkm & (0x8000 >> psw_key);
     }
     return true;
 }
-- 
2.31.1

Re: [PATCH for-8.0] target/s390x/tcg/mem_helper: Test the right bits in psw_key_valid()

[David Hildenbrand]

On 05.12.22 15:20, Thomas Huth wrote:
> The PSW key mask is a 16 bit field, and the psw_key variable is
> in the range from 0 to 15, so it does not make sense to use
> "0x80 >> psw_key" for testing the bits here. We should use 0x8000
> instead.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   Found by code inspection (Linux likely does not use these PSW key masks
>   yet, otherwise we might have noticed earlier)
> 
>   target/s390x/tcg/mem_helper.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
> index 9542fad59b..cb82cd1c1d 100644
> --- a/target/s390x/tcg/mem_helper.c
> +++ b/target/s390x/tcg/mem_helper.c
> @@ -51,7 +51,7 @@ static inline bool psw_key_valid(CPUS390XState *env, uint8_t psw_key)
>   
>       if (env->psw.mask & PSW_MASK_PSTATE) {
>           /* PSW key has range 0..15, it is valid if the bit is 1 in the PKM */
> -        return pkm & (0x80 >> psw_key);
> +        return pkm & (0x8000 >> psw_key);
>       }
>       return true;
>   }

I assume a Fixes tag might be applicable (I remember I added that once).

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH for-8.0] target/s390x/tcg/mem_helper: Test the right bits in psw_key_valid()

[Nina Schoetterl-Glausch]

On Mon, 2022-12-05 at 15:20 +0100, Thomas Huth wrote:
> The PSW key mask is a 16 bit field, and the psw_key variable is
> in the range from 0 to 15, so it does not make sense to use
> "0x80 >> psw_key" for testing the bits here. We should use 0x8000
> instead.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>

> ---
>  Found by code inspection (Linux likely does not use these PSW key masks
>  yet, otherwise we might have noticed earlier)
> 
>  target/s390x/tcg/mem_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
> index 9542fad59b..cb82cd1c1d 100644
> --- a/target/s390x/tcg/mem_helper.c
> +++ b/target/s390x/tcg/mem_helper.c
> @@ -51,7 +51,7 @@ static inline bool psw_key_valid(CPUS390XState *env, uint8_t psw_key)
>  
>      if (env->psw.mask & PSW_MASK_PSTATE) {
>          /* PSW key has range 0..15, it is valid if the bit is 1 in the PKM */
> -        return pkm & (0x80 >> psw_key);
> +        return pkm & (0x8000 >> psw_key);
>      }
>      return true;
>  }