[PATCH 6/9] KVM: arm64: PMU: Move the ID_AA64DFR0_EL1.PMUver limit to VM creation
Reiji Watanabe
reijiw at google.com
Thu Aug 25 23:02:21 PDT 2022
Hi Marc,
On Thu, Aug 25, 2022 at 9:34 PM Reiji Watanabe <reijiw at google.com> wrote:
>
> Hi Marc,
>
> On Fri, Aug 5, 2022 at 6:58 AM Marc Zyngier <maz at kernel.org> wrote:
> >
> > As further patches will enable the selection of a PMU revision
> > from userspace, sample the supported PMU revision at VM creation
> > time, rather than building each time the ID_AA64DFR0_EL1 register
> > is accessed.
> >
> > This shouldn't result in any change in behaviour.
> >
> > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > ---
> > arch/arm64/include/asm/kvm_host.h | 1 +
> > arch/arm64/kvm/arm.c | 6 ++++++
> > arch/arm64/kvm/pmu-emul.c | 11 +++++++++++
> > arch/arm64/kvm/sys_regs.c | 26 +++++++++++++++++++++-----
> > include/kvm/arm_pmu.h | 6 ++++++
> > 5 files changed, 45 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index f38ef299f13b..411114510634 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -163,6 +163,7 @@ struct kvm_arch {
> >
> > u8 pfr0_csv2;
> > u8 pfr0_csv3;
> > + u8 dfr0_pmuver;
> >
> > /* Hypercall features firmware registers' descriptor */
> > struct kvm_smccc_features smccc_feat;
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 8fe73ee5fa84..e4f80f0c1e97 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -164,6 +164,12 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> > set_default_spectre(kvm);
> > kvm_arm_init_hypercalls(kvm);
> >
> > + /*
> > + * Initialise the default PMUver before there is a chance to
> > + * create an actual PMU.
> > + */
> > + kvm->arch.dfr0_pmuver = kvm_arm_pmu_get_host_pmuver();
> > +
> > return ret;
> > out_free_stage2_pgd:
> > kvm_free_stage2_pgd(&kvm->arch.mmu);
> > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> > index ddd79b64b38a..33a88ca7b7fd 100644
> > --- a/arch/arm64/kvm/pmu-emul.c
> > +++ b/arch/arm64/kvm/pmu-emul.c
> > @@ -1021,3 +1021,14 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> >
> > return -ENXIO;
> > }
> > +
> > +u8 kvm_arm_pmu_get_host_pmuver(void)
>
> Nit: Since this function doesn't simply return the host's pmuver, but the
> pmuver limit for guests, perhaps "kvm_arm_pmu_get_guest_pmuver_limit"
> might be more clear (closer to what it does) ?
>
> > +{
> > + u64 tmp;
> > +
> > + tmp = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
> > + tmp = cpuid_feature_cap_perfmon_field(tmp,
> > + ID_AA64DFR0_PMUVER_SHIFT,
> > + ID_AA64DFR0_PMUVER_8_4);
> > + return FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER), tmp);
> > +}
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 333efddb1e27..55451f49017c 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -1062,6 +1062,22 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
> > return true;
> > }
> >
> > +static u8 pmuver_to_perfmon(const struct kvm_vcpu *vcpu)
> > +{
> > + if (!kvm_vcpu_has_pmu(vcpu))
> > + return 0;
> > +
> > + switch (vcpu->kvm->arch.dfr0_pmuver) {
> > + case ID_AA64DFR0_PMUVER_8_0:
> > + return ID_DFR0_PERFMON_8_0;
> > + case ID_AA64DFR0_PMUVER_IMP_DEF:
> > + return 0;
> > + default:
> > + /* Anything ARMv8.4+ has the same value. For now. */
> > + return vcpu->kvm->arch.dfr0_pmuver;
> > + }
> > +}
> > +
> > /* Read a sanitised cpufeature ID register by sys_reg_desc */
> > static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> > struct sys_reg_desc const *r, bool raz)
> > @@ -1112,10 +1128,10 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> > /* Limit debug to ARMv8.0 */
> > val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
> > val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6);
> > - /* Limit guests to PMUv3 for ARMv8.4 */
> > - val = cpuid_feature_cap_perfmon_field(val,
> > - ID_AA64DFR0_PMUVER_SHIFT,
> > - kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_4 : 0);
> > + /* Set PMUver to the required version */
> > + val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER);
> > + val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER),
> > + kvm_vcpu_has_pmu(vcpu) ? vcpu->kvm->arch.dfr0_pmuver : 0);
I've just noticed one issue in this patch while I'm reviewing patch-7.
I would think that this patch makes PMUVER and PERFMON inconsistent
when PMU is not enabled for the vCPU, and the host's sanitised PMUVER
is IMP_DEF.
Previously, when PMU is not enabled for the vCPU and the host's
sanitized value of PMUVER is IMP_DEF(0xf), the vCPU's PMUVER and PERFMON
are set to IMP_DEF due to a bug of cpuid_feature_cap_perfmon_field().
(https://lore.kernel.org/all/20220214065746.1230608-11-reijiw@google.com/)
With this patch, the vCPU's PMUVER will be 0 for the same case,
while the vCPU's PERFMON will stay the same (IMP_DEF).
I guess you unintentionally corrected only the PMUVER value of the VCPU.
Thank you,
Reiji
> > /* Hide SPE from guests */
> > val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
> > break;
> > @@ -1123,7 +1139,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> > /* Limit guests to PMUv3 for ARMv8.4 */
>
> Nit: I think the comment above should be removed like you did for
> ID_AA64DFR0_EL1 (or move it to kvm_arm_pmu_get_host_pmuver()?).
>
> Reviewed-by: Reiji Watanabe <reijiw at google.com>
>
> Thank you,
> Reiji
>
>
>
> > val = cpuid_feature_cap_perfmon_field(val,
> > ID_DFR0_PERFMON_SHIFT,
> > - kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_4 : 0);
> > + pmuver_to_perfmon(vcpu));
> > break;
> > }
> >
> > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> > index 96b192139a23..6bda9b071084 100644
> > --- a/include/kvm/arm_pmu.h
> > +++ b/include/kvm/arm_pmu.h
> > @@ -89,6 +89,8 @@ void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
> > vcpu->arch.pmu.events = *kvm_get_pmu_events(); \
> > } while (0)
> >
> > +u8 kvm_arm_pmu_get_host_pmuver(void);
> > +
> > #else
> > struct kvm_pmu {
> > };
> > @@ -154,6 +156,10 @@ static inline u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
> > static inline void kvm_pmu_update_vcpu_events(struct kvm_vcpu *vcpu) {}
> > static inline void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu) {}
> > static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}
> > +static inline u8 kvm_arm_pmu_get_host_pmuver(void)
> > +{
> > + return 0;
> > +}
> >
> > #endif
> >
> > --
> > 2.34.1
> >
> > _______________________________________________
> > kvmarm mailing list
> > kvmarm at lists.cs.columbia.edu
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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