[PATCH 8/9] KVM: arm64: PMU: Implement PMUv3p5 long counter support

[Reiji Watanabe]

On Wed, Aug 10, 2022 at 2:28 AM Marc Zyngier <maz at kernel.org> wrote:
>
> On Wed, 10 Aug 2022 08:16:14 +0100,
> Oliver Upton <oliver.upton at linux.dev> wrote:
> >
> > Hi Marc,
> >
> > On Fri, Aug 05, 2022 at 02:58:12PM +0100, Marc Zyngier wrote:
> > > PMUv3p5 (which is mandatory with ARMv8.5) comes with some extra
> > > features:
> > >
> > > - All counters are 64bit
> > >
> > > - The overflow point is controlled by the PMCR_EL0.LP bit
> > >
> > > Add the required checks in the helpers that control counter
> > > width and overflow, as well as the sysreg handling for the LP
> > > bit. A new kvm_pmu_is_3p5() helper makes it easy to spot the
> > > PMUv3p5 specific handling.
> > >
> > > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > > ---
> > >  arch/arm64/kvm/pmu-emul.c | 8 +++++---
> > >  arch/arm64/kvm/sys_regs.c | 4 ++++
> > >  include/kvm/arm_pmu.h     | 8 ++++++++
> > >  3 files changed, 17 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> > > index 33a88ca7b7fd..b33a2953cbf6 100644
> > > --- a/arch/arm64/kvm/pmu-emul.c
> > > +++ b/arch/arm64/kvm/pmu-emul.c
> > > @@ -50,13 +50,15 @@ static u32 kvm_pmu_event_mask(struct kvm *kvm)
> > >   */
> > >  static bool kvm_pmu_idx_is_64bit(struct kvm_vcpu *vcpu, u64 select_idx)
> > >  {
> > > -   return (select_idx == ARMV8_PMU_CYCLE_IDX);
> > > +   return (select_idx == ARMV8_PMU_CYCLE_IDX || kvm_pmu_is_3p5(vcpu));
> > >  }
> > >
> > >  static bool kvm_pmu_idx_has_64bit_overflow(struct kvm_vcpu *vcpu, u64 select_idx)
> > >  {
> > > -   return (select_idx == ARMV8_PMU_CYCLE_IDX &&
> > > -           __vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_LC);
> > > +   u64 val = __vcpu_sys_reg(vcpu, PMCR_EL0);
> > > +
> > > +   return (select_idx < ARMV8_PMU_CYCLE_IDX && (val & ARMV8_PMU_PMCR_LP)) ||
> > > +          (select_idx == ARMV8_PMU_CYCLE_IDX && (val & ARMV8_PMU_PMCR_LC));
> > >  }
> > >
> > >  static bool kvm_pmu_counter_can_chain(struct kvm_vcpu *vcpu, u64 idx)
> > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > > index c0595f31dab8..2b5e0ec5c100 100644
> > > --- a/arch/arm64/kvm/sys_regs.c
> > > +++ b/arch/arm64/kvm/sys_regs.c
> > > @@ -654,6 +654,8 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> > >            | (ARMV8_PMU_PMCR_MASK & 0xdecafbad)) & (~ARMV8_PMU_PMCR_E);

Not directly related to this series, but using 0xdecafbad above
appears to be odd. I think that would lead the bit 3 and 5 to be
unconditionally set in the register's reset value that the guest will
initially see even on the configuration where those should be RES0.

> > >     if (!system_supports_32bit_el0())
> > >             val |= ARMV8_PMU_PMCR_LC;
> > > +   if (!kvm_pmu_is_3p5(vcpu))
> > > +           val &= ~ARMV8_PMU_PMCR_LP;
> > >     __vcpu_sys_reg(vcpu, r->reg) = val;
> > >  }
> > >
> > > @@ -703,6 +705,8 @@ static bool access_pmcr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> > >             val |= p->regval & ARMV8_PMU_PMCR_MASK;
> > >             if (!system_supports_32bit_el0())
> > >                     val |= ARMV8_PMU_PMCR_LC;
> > > +           if (!kvm_pmu_is_3p5(vcpu))
> > > +                   val &= ~ARMV8_PMU_PMCR_LP;
> > >             __vcpu_sys_reg(vcpu, PMCR_EL0) = val;
> > >             kvm_pmu_handle_pmcr(vcpu, val);
> > >             kvm_vcpu_pmu_restore_guest(vcpu);
> > > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> > > index 6bda9b071084..846502251923 100644
> > > --- a/include/kvm/arm_pmu.h
> > > +++ b/include/kvm/arm_pmu.h
> > > @@ -89,6 +89,13 @@ void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
> > >                     vcpu->arch.pmu.events = *kvm_get_pmu_events();  \
> > >     } while (0)
> > >
> > > +/*
> > > + * Evaluates as true when emulating PMUv3p5, and false otherwise.
> > > + */
> > > +#define kvm_pmu_is_3p5(vcpu)                                               \
> > > +   (vcpu->kvm->arch.dfr0_pmuver >= ID_AA64DFR0_PMUVER_8_5 &&       \
> > > +    vcpu->kvm->arch.dfr0_pmuver != ID_AA64DFR0_PMUVER_IMP_DEF)
> >
> > I don't believe the IMP_DEF condition will ever evaluate to false as
> > dfr0_pmuver is sanitized at initialization and writes from userspace.
>
> Good point. That's a leftover from a previous version. I'll fix that.

With the current series, I think the dfr0_pmuver could be IMP_DEF
due to the same bug that I mentioned for the patch-6.
(https://lore.kernel.org/all/20220214065746.1230608-11-reijiw@google.com/)

Thank you,
Reiji