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

[Marc Zyngier <maz@kernel.org>]

On Tue, 13 Jul 2021 15:39:49 +0100,
"Russell King (Oracle)" <linux@armlinux.org.uk> 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,

	M.

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