Re: [PATCH V2] arm/kvm: add support for MTE

[Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>]

On 19-09-2024 08:35 pm, Cornelia Huck wrote:
> On Thu, Sep 19 2024, Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com> wrote:
> 
>> I have modified as below diff to keep TCG if loop as it is and adding if
>> for KVM case to clear/mask the MTE bits if MTE in KVM mode is not
>> enabled by user command(if no mte=on).
>>
>> Is below diff makes sense?
>>
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index a59417aac8..523996576d 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -2390,15 +2390,20 @@ static void arm_cpu_realizefn(DeviceState *dev,
>> Error **errp)
>>
>>    #ifndef CONFIG_USER_ONLY
>>            /*
>> -         * If we do not have tag-memory provided by the TCG
>> -         * nor MTE at KVM enabled, reduce MTE support to
>> -         * instructions enabled at EL0.
>> +         * If we do not have tag-memory provided by the TCG,
>> +         * reduce MTE support to instructions enabled at EL0.
>>             * This matches Cortex-A710 BROADCASTMTE input being LOW.
>>             */
>> -        if (cpu->tag_memory == NULL && !cpu->kvm_mte) {
>> +        if (tcg_enabled() && cpu->tag_memory == NULL) {
>>                cpu->isar.id_aa64pfr1 =
>>                    FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 1);
>>            }
>> +
>> +        /* Disable MTE, if it is not enabled by the user for KVM mode.
>> +         */
>> +        if (kvm_enabled() && !cpu->kvm_mte) {
>> +                FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 0);
>> +        }
>>    #endif
>>        }
> 
> Wouldn't that be a possibly guest-visible change?
> 

Yes, the MTE bits of id_aa64pfr1 are masked to guest like before.

-- 
Thanks,
Ganapat/GK