[RFC PATCH v4 22/26] KVM: arm64: Trap disabled features of ID_AA64DFR0_EL1

[Reiji Watanabe]

Hi Fuad,

On Mon, Jan 24, 2022 at 9:20 AM Fuad Tabba <tabba at google.com> wrote:
>
> .Hi Reiji,
>
> On Thu, Jan 6, 2022 at 4:29 AM Reiji Watanabe <reijiw at google.com> wrote:
> >
> > Add feature_config_ctrl for PMUv3, PMS and TraceFilt, which are
> > indicated in ID_AA64DFR0_EL1, to program configuration registers
> > to trap guest's using those features when they are not exposed to
> > the guest.
> >
> > Signed-off-by: Reiji Watanabe <reijiw at google.com>
> > ---
> >  arch/arm64/kvm/sys_regs.c | 47 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 72e745c5a9c2..229671ec3abd 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -349,6 +349,22 @@ static void feature_mte_trap_activate(struct kvm_vcpu *vcpu)
> >         feature_trap_activate(vcpu, VCPU_HCR_EL2, HCR_TID5, HCR_DCT | HCR_ATA);
> >  }
> >
> > +static void feature_pmuv3_trap_activate(struct kvm_vcpu *vcpu)
> > +{
> > +       feature_trap_activate(vcpu, VCPU_MDCR_EL2, MDCR_EL2_TPM, 0);
>
> I think that for full coverage it might be good to include setting
> MDCR_EL2_TPMCR, and clearing MDCR_EL2_HPME | MDCR_EL2_MTPME |
> MDCR_EL2_HPMN_MASK, even if redundant at this point.

I included what is needed only, and I would prefer not to let KVM
do things that are not needed to trap guest's using the feature.
Please let me know if you have a specific reason why you think it
would be better to include them.

>
> > +}
> > +
> > +static void feature_pms_trap_activate(struct kvm_vcpu *vcpu)
> > +{
> > +       feature_trap_activate(vcpu, VCPU_MDCR_EL2, MDCR_EL2_TPMS,
> > +                             MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT);
> > +}
> > +
> > +static void feature_tracefilt_trap_activate(struct kvm_vcpu *vcpu)
> > +{
> > +       feature_trap_activate(vcpu, VCPU_MDCR_EL2, MDCR_EL2_TTRF, 0);
> > +}
> > +
> >  /* For ID_AA64PFR0_EL1 */
> >  static struct feature_config_ctrl ftr_ctrl_ras = {
> >         .ftr_reg = SYS_ID_AA64PFR0_EL1,
> > @@ -375,6 +391,31 @@ static struct feature_config_ctrl ftr_ctrl_mte = {
> >         .trap_activate = feature_mte_trap_activate,
> >  };
> >
> > +/* For ID_AA64DFR0_EL1 */
> > +static struct feature_config_ctrl ftr_ctrl_pmuv3 = {
> > +       .ftr_reg = SYS_ID_AA64DFR0_EL1,
> > +       .ftr_shift = ID_AA64DFR0_PMUVER_SHIFT,
> > +       .ftr_min = ID_AA64DFR0_PMUVER_8_0,
> > +       .ftr_signed = FTR_UNSIGNED,
> > +       .trap_activate = feature_pmuv3_trap_activate,
> > +};
> > +
> > +static struct feature_config_ctrl ftr_ctrl_pms = {
> > +       .ftr_reg = SYS_ID_AA64DFR0_EL1,
> > +       .ftr_shift = ID_AA64DFR0_PMSVER_SHIFT,
> > +       .ftr_min = ID_AA64DFR0_PMSVER_8_2,
> > +       .ftr_signed = FTR_UNSIGNED,
> > +       .trap_activate = feature_pms_trap_activate,
> > +};
> > +
> > +static struct feature_config_ctrl ftr_ctrl_tracefilt = {
> > +       .ftr_reg = SYS_ID_AA64DFR0_EL1,
> > +       .ftr_shift = ID_AA64DFR0_TRACE_FILT_SHIFT,
> > +       .ftr_min = 1,
> > +       .ftr_signed = FTR_UNSIGNED,
> > +       .trap_activate = feature_tracefilt_trap_activate,
> > +};
>
> I think you might be missing trace, ID_AA64DFR0_TRACEVER -> CPTR_EL2_TTA.

Thank you for catching this. I will add the trace.

Thanks,
Reiji