linux-kernel - [PATCH v2 2/3] KVM: x86/svm/pmu: Direct access pmu->gp_counter[] to implement amd_*_to

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Message-Id: <20220520144512.88454-1-likexu@tencent.com>
Date:   Fri, 20 May 2022 22:45:12 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     pbonzini@...hat.com
Cc:     jmattson@...gle.com, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com
Subject: [PATCH v2 2/3] KVM: x86/svm/pmu: Direct access pmu->gp_counter[] to implement amd_*_to_pmc()

From: Like Xu <likexu@...cent.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@...cent.com>
---
v1 -> v2 Changelog:
- Remove unused helper get_msr_base();

 arch/x86/kvm/svm/pmu.c | 45 +++++++-----------------------------------
 1 file changed, 7 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index a3b78342a221..6cd8d3c2000c 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -61,21 +61,14 @@ static struct kvm_event_hw_type_mapping amd_f17h_event_mapping[] = {
 static_assert(ARRAY_SIZE(amd_event_mapping) ==
 	     ARRAY_SIZE(amd_f17h_event_mapping));
 
-static unsigned int get_msr_base(struct kvm_pmu *pmu, enum pmu_type type)
+static struct kvm_pmc *amd_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
 {
-	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)) {
-		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;
-	}
+	if (pmc_idx >= num_counters)
+		return NULL;
+
+	return &pmu->gp_counters[array_index_nospec(pmc_idx, num_counters)];
 }
 
 static enum index msr_to_index(u32 msr)
@@ -186,22 +179,6 @@ static bool amd_pmc_is_enabled(struct kvm_pmc *pmc)
 	return true;
 }
 
-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);
-
-	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;
-	}
-
-	return get_gp_pmc_amd(pmu, base + pmc_idx, PMU_TYPE_COUNTER);
-}
-
 static bool amd_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
@@ -215,15 +192,7 @@ 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)
-- 
2.36.1