On Tue, 29 Jun 2021 14:16:55 +0100,
Alexandre Chartre <alexandre.chartre@xxxxxxxxxx> wrote:
>
>
> Hi Marc,
>
> On 6/29/21 11:06 AM, Marc Zyngier wrote:
> > Hi Alexandre,
[...]
> > So the sysreg is the only thing we should consider, and I think we
> > should drop the useless masking. There is at least another instance of
> > this in the PMU code (kvm_pmu_overflow_status()), and apart from
> > kvm_pmu_vcpu_reset(), only the sysreg accessors should care about the
> > masking to sanitise accesses.
> >
> > What do you think?
> >
>
> I think you are right. PMCNTENSET_EL0 is already masked with
> kvm_pmu_valid_counter_mask() so there's effectively no need to mask
> it again when we use it. I will send an additional patch (on top of
> this one) to remove useless masking. Basically, changes would be:
>
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index bab4b735a0cf..e0dfd7ce4ba0 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -373,7 +373,6 @@ static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
> reg = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
> reg &= __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
> reg &= __vcpu_sys_reg(vcpu, PMINTENSET_EL1);
> - reg &= kvm_pmu_valid_counter_mask(vcpu);
> }
> return reg;
> @@ -564,21 +563,22 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
> */
> void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
> {
> - unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
> + unsigned long mask;
> int i;
> if (val & ARMV8_PMU_PMCR_E) {
> kvm_pmu_enable_counter_mask(vcpu,
> - __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
> + __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
> } else {
> kvm_pmu_disable_counter_mask(vcpu,
> - __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
> + __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
> }
> if (val & ARMV8_PMU_PMCR_C)
> kvm_pmu_set_counter_value(vcpu, ARMV8_PMU_CYCLE_IDX, 0);
> if (val & ARMV8_PMU_PMCR_P) {
> + mask = kvm_pmu_valid_counter_mask(vcpu);
Careful here, this clashes with a fix from Alexandru that is currently
in -next (PMCR_EL0.P shouldn't reset the cycle counter) and aimed at
5.14. And whilst you're at it, consider moving the 'mask' declaration
here too.
> for_each_set_bit(i, &mask, 32)
> kvm_pmu_set_counter_value(vcpu, i, 0);
> }
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1a7968ad078c..2e406905760e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -845,7 +845,7 @@ static bool access_pmcnten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> kvm_pmu_disable_counter_mask(vcpu, val);
> }
> } else {
> - p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
> + p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
> }
> return true;
If you are cleaning up the read-side of sysregs, access_pminten() and
access_pmovs() could have some of your attention too.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
