target/arm: Disable SVE extensions when SVE is disabled

[PATCH] target/arm: Disable SVE extensions when SVE is disabled

Posted by Richard Henderson 6 months ago

From: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2304
Reported-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---

Marcin added the correct patch to the issue 3 weeks ago, so I'm giving
him authorship here.  I only updated the comment a bit.
Marcin, if you'd reply to this with your s-o-b, that would be helpful.

r~

---
 target/arm/cpu64.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index c15d086049..862d2b92fa 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -109,7 +109,11 @@ void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp)
          * No explicit bits enabled, and no implicit bits from sve-max-vq.
          */
         if (!cpu_isar_feature(aa64_sve, cpu)) {
-            /* SVE is disabled and so are all vector lengths.  Good. */
+            /*
+             * SVE is disabled and so are all vector lengths.  Good.
+             * Disable all SVE extensions as well.
+             */
+            cpu->isar.id_aa64zfr0 = 0;
             return;
         }
 
-- 
2.34.1

Re: [PATCH] target/arm: Disable SVE extensions when SVE is disabled

Posted by Peter Maydell 5 months, 4 weeks ago

On Sun, 26 May 2024 at 21:46, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> From: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
>
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2304
> Reported-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---

Applied to target-arm.next, thanks.

(Looks like we already got this right for SME:
arm_cpu_sme_finalize() clears ID_AA64SMFR0_EL1 if
SME is disabled.)

-- PMM

Re: [PATCH] target/arm: Disable SVE extensions when SVE is disabled

Posted by Marcin Juszkiewicz 6 months ago

W dniu 26.05.2024 o 22:45, Richard Henderson pisze:
> From: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
> 
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2304
> Reported-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>

> ---
> 
> Marcin added the correct patch to the issue 3 weeks ago, so I'm giving
> him authorship here.  I only updated the comment a bit.

I am not fully sure is it everything needed to be honest.

Value 0x0000 in [3:0] means "The SVE instructions are implemented".

The way why it works is probably because QEMU keeps "there is no SVE" 
information separately and do not emulate them.

> Marcin, if you'd reply to this with your s-o-b, that would be helpful.

done


> r~
> 
> ---
>   target/arm/cpu64.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> index c15d086049..862d2b92fa 100644
> --- a/target/arm/cpu64.c
> +++ b/target/arm/cpu64.c
> @@ -109,7 +109,11 @@ void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp)
>            * No explicit bits enabled, and no implicit bits from sve-max-vq.
>            */
>           if (!cpu_isar_feature(aa64_sve, cpu)) {
> -            /* SVE is disabled and so are all vector lengths.  Good. */
> +            /*
> +             * SVE is disabled and so are all vector lengths.  Good.
> +             * Disable all SVE extensions as well.
> +             */
> +            cpu->isar.id_aa64zfr0 = 0;
>               return;
>           }
>

Re: [PATCH] target/arm: Disable SVE extensions when SVE is disabled

Posted by Richard Henderson 6 months ago

On 5/26/24 14:06, Marcin Juszkiewicz wrote:
> W dniu 26.05.2024 o 22:45, Richard Henderson pisze:
>> From: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
>>
>> Cc: qemu-stable@nongnu.org
>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2304
>> Reported-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> 
> Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
> 
>> ---
>>
>> Marcin added the correct patch to the issue 3 weeks ago, so I'm giving
>> him authorship here.  I only updated the comment a bit.
> 
> I am not fully sure is it everything needed to be honest.
> 
> Value 0x0000 in [3:0] means "The SVE instructions are implemented".
> 
> The way why it works is probably because QEMU keeps "there is no SVE" information 
> separately and do not emulate them.

ID_AA64PFR0_EL1.SVE is the primary indicator for SVE.


r~