KVM: x86/pmu: Move pmc_idx => pmc translation helper to common code

Add a common helper for *internal* PMC lookups, and delete the ops hook
and Intel's implementation.  Keep AMD's implementation, but rename it to
amd_pmu_get_pmc() to make it somewhat more obvious that it's suited for
both KVM-internal and guest-initiated lookups.

Because KVM tracks all counters in a single bitmap, getting a counter
when iterating over a bitmap, e.g. of all valid PMCs, requires a small
amount of math, that while simple, isn't super obvious and doesn't use the
same semantics as PMC lookups from RDPMC!  Although AMD doesn't support
fixed counters, the common PMU code still behaves as if there a split, the
high half of which just happens to always be empty.

Opportunstically add a comment to explain both what is going on, and why
KVM uses a single bitmap, e.g. the boilerplate for iterating over separate
bitmaps could be done via macros, so it's not (just) about deduplicating
code.

Link: https://lore.kernel.org/r/20231110022857.1273836-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index e886300f0f97..dfcc38bd97d3 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -25,7 +25,7 @@ enum pmu_type {
 	PMU_TYPE_EVNTSEL,
 };
 
-static struct kvm_pmc *amd_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
+static struct kvm_pmc *amd_pmu_get_pmc(struct kvm_pmu *pmu, int pmc_idx)
 {
 	unsigned int num_counters = pmu->nr_arch_gp_counters;
 
@@ -70,7 +70,7 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
 		return NULL;
 	}
 
-	return amd_pmc_idx_to_pmc(pmu, idx);
+	return amd_pmu_get_pmc(pmu, idx);
 }
 
 static int amd_check_rdpmc_early(struct kvm_vcpu *vcpu, unsigned int idx)
@@ -87,7 +87,7 @@ static int amd_check_rdpmc_early(struct kvm_vcpu *vcpu, unsigned int idx)
 static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
 	unsigned int idx, u64 *mask)
 {
-	return amd_pmc_idx_to_pmc(vcpu_to_pmu(vcpu), idx);
+	return amd_pmu_get_pmc(vcpu_to_pmu(vcpu), idx);
 }
 
 static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)
@@ -229,7 +229,6 @@ static void amd_pmu_init(struct kvm_vcpu *vcpu)
 }
 
 struct kvm_pmu_ops amd_pmu_ops __initdata = {
-	.pmc_idx_to_pmc = amd_pmc_idx_to_pmc,
 	.rdpmc_ecx_to_pmc = amd_rdpmc_ecx_to_pmc,
 	.msr_idx_to_pmc = amd_msr_idx_to_pmc,
 	.check_rdpmc_early = amd_check_rdpmc_early,