Re: [PATCH 1/2] KVM: x86/pmu: Define KVM_PMC_MAX_GENERIC for platform independence

Sean Christopherson
2024-06-21T13:48:45Z

On Fri, Jun 21, 2024, Dapeng Mi wrote:
> >> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> >> index 6e908bdc3310..2fca247798eb 100644
> >> --- a/arch/x86/kvm/svm/pmu.c
> >> +++ b/arch/x86/kvm/svm/pmu.c
> >> @@ -218,7 +218,7 @@ static void amd_pmu_init(struct kvm_vcpu *vcpu)
> >> int i;
> >>
> >> BUILD_BUG_ON(KVM_AMD_PMC_MAX_GENERIC > AMD64_NUM_COUNTERS_CORE);
> >> - BUILD_BUG_ON(KVM_AMD_PMC_MAX_GENERIC > INTEL_PMC_MAX_GENERIC);
> >> + BUILD_BUG_ON(KVM_AMD_PMC_MAX_GENERIC > KVM_PMC_MAX_GENERIC);
> >>
> >> for (i = 0; i < KVM_AMD_PMC_MAX_GENERIC ; i++) {
> >> pmu->gp_counters[i].type = KVM_PMC_GP;
> >> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> >> index fb5cbd6cbeff..a4b0bee04596 100644
> >> --- a/arch/x86/kvm/vmx/pmu_intel.c
> >> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> >> @@ -570,6 +570,8 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
> >> struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> >> struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
> >>
> >> + BUILD_BUG_ON(KVM_INTEL_PMC_MAX_GENERIC > KVM_PMC_MAX_GENERIC);
> > Rather than BUILD_BUG_ON() for both Intel and AMD, can't we just do?
> >
> > #define KVM_MAX_NR_GP_COUNTERS max(KVM_INTEL_PMC_MAX_GENERIC, KVM_AMD_PMC_MAX_GENERIC)
>
> Actually I tried this, but compiler would report the below error since
> KVM_PMC_MAX_GENERIC would used to define the array
> gp_counters[KVM_PMC_MAX_GENERIC];
>
> ./include/linux/minmax.h:48:50: error: braced-group within expression
> allowed only inside a function

Oh, right, the min/max macros are super fancy to deal with types. How about this
(getting there over 2-3 patches)?

I don't love the "#define MAX", but I don't see a better option. I suppose maybe
we should use __MAX or KVM_MAX since kvm_host.h is likely included outside of KVM?

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5c0415899a07..ce0c9191eb85 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -532,13 +532,18 @@ struct kvm_pmc {
u64 current_config;
};

+#define MAX(a, b) ((a) >= (b) ? (a) : (b))
+
/* More counters may conflict with other existing Architectural MSRs */
-#define KVM_INTEL_PMC_MAX_GENERIC 8
-#define MSR_ARCH_PERFMON_PERFCTR_MAX (MSR_ARCH_PERFMON_PERFCTR0 + KVM_INTEL_PMC_MAX_GENERIC - 1)
-#define MSR_ARCH_PERFMON_EVENTSEL_MAX (MSR_ARCH_PERFMON_EVENTSEL0 + KVM_INTEL_PMC_MAX_GENERIC - 1)
-#define KVM_PMC_MAX_FIXED 3
-#define MSR_ARCH_PERFMON_FIXED_CTR_MAX (MSR_ARCH_PERFMON_FIXED_CTR0 + KVM_PMC_MAX_FIXED - 1)
-#define KVM_AMD_PMC_MAX_GENERIC 6
+#define KVM_MAX_NR_INTEL_GP_COUNTERS 8
+#define KVM_MAX_NR_AMD_GP_COUNTERS 6
+#define KVM_MAX_NR_GP_COUNTERS MAX(KVM_MAX_NR_INTEL_GP_COUNTERS, \
+ KVM_MAX_NR_AMD_GP_COUNTERS)
+
+#define KVM_MAX_NR_INTEL_FIXED_COUTNERS 3
+#define KVM_MAX_NR_AMD_FIXED_COUTNERS 0
+#define KVM_MAX_NR_FIXED_COUNTERS MAX(KVM_MAX_NR_INTEL_FIXED_COUTNERS, \
+ KVM_MAX_NR_AMD_FIXED_COUTNERS)

struct kvm_pmu {
u8 version;
@@ -554,8 +559,8 @@ struct kvm_pmu {
u64 global_status_rsvd;
u64 reserved_bits;
u64 raw_event_mask;
- struct kvm_pmc gp_counters[KVM_INTEL_PMC_MAX_GENERIC];
- struct kvm_pmc fixed_counters[KVM_PMC_MAX_FIXED];
+ struct kvm_pmc gp_counters[KVM_MAX_NR_GP_COUNTERS];
+ struct kvm_pmc fixed_counters[KVM_MAX_NR_FIXED_COUNTERS];

/*
* Overlay the bitmap with a 64-bit atomic so that all bits can be