Subject: Re: [PATCH 1/3] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 13 Jul 2021 17:15:44 +0100

On Tue, Jul 13, 2021 at 04:59:58PM +0100, Marc Zyngier wrote:
> On Tue, 13 Jul 2021 15:39:49 +0100,
> "Russell King (Oracle)" <[email-masked]> wrote:
> > 
> > On Tue, Jul 13, 2021 at 02:58:58PM +0100, Marc Zyngier wrote:
> > > +static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> > > +{
> > > +	u64 n, mask;
> > > +
> > > +	/* No PMU available, any PMU reg may UNDEF... */
> > > +	if (!kvm_arm_support_pmu_v3())
> > > +		return;
> > > +
> > > +	n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
> > > +	n &= ARMV8_PMU_PMCR_N_MASK;
> > > +
> > > +	reset_unknown(vcpu, r);
> > > +
> > > +	mask = BIT(ARMV8_PMU_CYCLE_IDX);
> > > +	if (n)
> > > +		mask |= GENMASK(n - 1, 0);
> > > +
> > > +	__vcpu_sys_reg(vcpu, r->reg) &= mask;
> > 
> > Would this read more logically to structure it as:
> > 
> > 	mask = BIT(ARMV8_PMU_CYCLE_IDX);
> > 
> > 	n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
> > 	n &= ARMV8_PMU_PMCR_N_MASK;
> > 	if (n)
> > 		mask |= GENMASK(n - 1, 0);
> > 
> > 	reset_unknown(vcpu, r);
> > 	__vcpu_sys_reg(vcpu, r->reg) &= mask;
> > 
> > ?
> 
> Yup, that's nicer. Amended locally.

Thanks Marc.

For the whole series:

Acked-by: Russell King (Oracle) <[email-masked]>

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