Re: [PATCH v7 07/12] KVM: arm64: PMU: Set PMCR_EL0.N for vCPU based on the associated PMU

[Raghavendra Rao Ananta]

On Mon, Oct 16, 2023 at 6:35 AM Sebastian Ott <sebott@xxxxxxxxxx> wrote:
>
> On Mon, 9 Oct 2023, Raghavendra Rao Ananta wrote:
> > u64 kvm_vcpu_read_pmcr(struct kvm_vcpu *vcpu)
> > {
> > -     return __vcpu_sys_reg(vcpu, PMCR_EL0);
> > +     u64 pmcr = __vcpu_sys_reg(vcpu, PMCR_EL0) &
> > +                     ~(ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
> > +
> > +     return pmcr | ((u64)vcpu->kvm->arch.pmcr_n << ARMV8_PMU_PMCR_N_SHIFT);
> > }
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index ff0f7095eaca..c750722fbe4a 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -745,12 +745,8 @@ static u64 reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> > {
> >       u64 pmcr;
> >
> > -     /* No PMU available, PMCR_EL0 may UNDEF... */
> > -     if (!kvm_arm_support_pmu_v3())
> > -             return 0;
> > -
> >       /* Only preserve PMCR_EL0.N, and reset the rest to 0 */
> > -     pmcr = read_sysreg(pmcr_el0) & (ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
> > +     pmcr = kvm_vcpu_read_pmcr(vcpu) & (ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
>
> pmcr = ((u64)vcpu->kvm->arch.pmcr_n << ARMV8_PMU_PMCR_N_SHIFT);
> Would that maybe make it more clear what is done here?
>
Since we require the entire PMCR register, and not just the PMCR.N
field, I think using kvm_vcpu_read_pmcr() would be technically
correct, don't you think?

Thank you.
Raghavendra