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

[Ganapatrao Kulkarni]

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