[PATCH v4 3/4] KVM: arm64: Enable writable for ID_AA64PFR0_EL1

[Jing Zhang]

Hi Oliver,

On Mon, Jun 26, 2023 at 9:49 AM Oliver Upton <oliver.upton at linux.dev> wrote:
>
> On Wed, Jun 07, 2023 at 07:45:53PM +0000, Jing Zhang wrote:
> > Return an error if userspace tries to set SVE field of the register
> > to a value that conflicts with SVE configuration for the guest.
> > SIMD/FP/SVE fields of the requested value are validated according to
> > Arm ARM.
> >
> > Signed-off-by: Jing Zhang <jingzhangos at google.com>
> > ---
> >  arch/arm64/kvm/sys_regs.c | 31 +++++++++++++++++++++++++++++--
> >  1 file changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 3964a85a89fe..8f3ad9c12b27 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -1509,9 +1509,36 @@ static u64 read_sanitised_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> >
> >       val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_AMU);
> >
> > +     if (!system_supports_sve())
> > +             val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_SVE);
> > +
>
> If the system doesn't support SVE, wouldn't the sanitised system-wide
> value hide the feature as well? A few lines up we already mask this
> field based on whether or not the vCPU has the feature, which is
> actually meaningful.
Yes, you are right. This change is not needed actually.
>
> >       return val;
> >  }
> >
> > +static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> > +                            const struct sys_reg_desc *rd,
> > +                            u64 val)
> > +{
> > +     int fp, simd;
> > +     bool has_sve = id_aa64pfr0_sve(val);
> > +
> > +     simd = cpuid_feature_extract_signed_field(val, ID_AA64PFR0_EL1_AdvSIMD_SHIFT);
> > +     fp = cpuid_feature_extract_signed_field(val, ID_AA64PFR0_EL1_FP_SHIFT);
> > +     /* AdvSIMD field must have the same value as FP field */
> > +     if (simd != fp)
> > +             return -EINVAL;
> > +
> > +     /* fp must be supported when sve is supported */
> > +     if (has_sve && (fp < 0))
> > +             return -EINVAL;
> > +
> > +     /* Check if there is a conflict with a request via KVM_ARM_VCPU_INIT */
> > +     if (vcpu_has_sve(vcpu) ^ has_sve)
> > +             return -EPERM;
>
> Same comment here on cross-field plumbing.
Will fix.
>
> --
> Thanks,
> Oliver

Thanks,
Jing