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

[Marc Zyngier <maz@kernel.org>]

On Wed, 10 Aug 2022 08:16:14 +0100,
Oliver Upton <oliver.upton@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@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);
> >  	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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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