Re: [PATCH v6 05/16] KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter

[Xu, Like]

On 2021/5/17 16:18, Peter Zijlstra wrote:
> On Tue, May 11, 2021 at 10:42:03AM +0800, Like Xu wrote:
> > The mask value of fixed counter control register should be dynamic
> > adjusted with the number of fixed counters. This patch introduces a
> > variable that includes the reserved bits of fixed counter control
> > registers. This is needed for later Ice Lake fixed counter changes.
> >
> > Co-developed-by: Luwei Kang <luwei.kang@xxxxxxxxx>
> > Signed-off-by: Luwei Kang <luwei.kang@xxxxxxxxx>
> > Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_host.h | 1 +
> >   arch/x86/kvm/vmx/pmu_intel.c    | 6 +++++-
> >   2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 55efbacfc244..49b421bd3dd8 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -457,6 +457,7 @@ struct kvm_pmu {
> >   	unsigned nr_arch_fixed_counters;
> >   	unsigned available_event_types;
> >   	u64 fixed_ctr_ctrl;
> > +	u64 fixed_ctr_ctrl_mask;
> >   	u64 global_ctrl;
> >   	u64 global_status;
> >   	u64 global_ovf_ctrl;
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index d9dbebe03cae..ac7fe714e6c1 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -400,7 +400,7 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >   	case MSR_CORE_PERF_FIXED_CTR_CTRL:
> >   		if (pmu->fixed_ctr_ctrl == data)
> >   			return 0;
> > -		if (!(data & 0xfffffffffffff444ull)) {
> > +		if (!(data & pmu->fixed_ctr_ctrl_mask)) {
> Don't we already have hardware with more than 3 fixed counters?

Yes, so we update this mask based on the value of pmu->nr_arch_fixed_counters:

+    for (i = 0; i < pmu->nr_arch_fixed_counters; i++)
+        pmu->fixed_ctr_ctrl_mask &= ~(0xbull << (i * 4));

I assume this comment will not result in any code changes for this patch.