[PATCH v2 1/2] KVM: x86/svm/pmu: Direct access pmu->gp_counter[] to implement amd_*_to_pmc()

[Like Xu <like.xu.linux@gmail.com>]

From: Like Xu <likexu@tencent.com>

AMD only has gp counters, whose corresponding vPMCs are initialised
and stored in pmu->gp_counter[] in order of idx, so we can access this
array directly based on any valid pmc->idx, without any help from other
interfaces at all. The amd_rdpmc_ecx_to_pmc() can now reuse this part
of the code quite naturally.

Opportunistically apply array_index_nospec() to reduce the attack
surface for speculative execution and remove the dead code.

Signed-off-by: Like Xu <likexu@tencent.com>
---
v1: https://lore.kernel.org/kvm/20220510115718.93335-2-likexu@tencent.com/
v1 -> v2 Changelog:
- Remove unused helper get_msr_base();

 arch/x86/kvm/svm/pmu.c | 41 +++++------------------------------------
 1 file changed, 5 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index f24613a108c5..d1c3b766841e 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -33,23 +33,6 @@ enum index {
 	INDEX_ERROR,
 };
 
-static unsigned int get_msr_base(struct kvm_pmu *pmu, enum pmu_type type)
-{
-	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
-
-	if (guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE)) {
-		if (type == PMU_TYPE_COUNTER)
-			return MSR_F15H_PERF_CTR;
-		else
-			return MSR_F15H_PERF_CTL;
-	} else {
-		if (type == PMU_TYPE_COUNTER)
-			return MSR_K7_PERFCTR0;
-		else
-			return MSR_K7_EVNTSEL0;
-	}
-}
-
 static enum index msr_to_index(u32 msr)
 {
 	switch (msr) {
@@ -141,18 +124,12 @@ static bool amd_pmc_is_enabled(struct kvm_pmc *pmc)
 
 static struct kvm_pmc *amd_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
 {
-	unsigned int base = get_msr_base(pmu, PMU_TYPE_COUNTER);
-	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
+	unsigned int num_counters = pmu->nr_arch_gp_counters;
 
-	if (guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE)) {
-		/*
-		 * The idx is contiguous. The MSRs are not. The counter MSRs
-		 * are interleaved with the event select MSRs.
-		 */
-		pmc_idx *= 2;
-	}
+	if (pmc_idx >= num_counters)
+		return NULL;
 
-	return get_gp_pmc_amd(pmu, base + pmc_idx, PMU_TYPE_COUNTER);
+	return &pmu->gp_counters[array_index_nospec(pmc_idx, num_counters)];
 }
 
 static bool amd_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
@@ -168,15 +145,7 @@ static bool amd_is_valid_rdpmc_ecx(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)
 {
-	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
-	struct kvm_pmc *counters;
-
-	idx &= ~(3u << 30);
-	if (idx >= pmu->nr_arch_gp_counters)
-		return NULL;
-	counters = pmu->gp_counters;
-
-	return &counters[idx];
+	return amd_pmc_idx_to_pmc(vcpu_to_pmu(vcpu), idx & ~(3u << 30));
 }
 
 static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
-- 
2.37.1