[PATCH 01/10] KVM: x86/pmu: Zero out PMU metadata on AMD if PMU is disabled

Sean Christopherson
2023-11-10T02:29:04Z

Move the purging of common PMU metadata from intel_pmu_refresh() to
kvm_pmu_refresh(), and invoke the vendor refresh() hook if and only if
the VM is supposed to have a vPMU.

KVM already denies access to the PMU based on kvm->arch.enable_pmu, as
get_gp_pmc_amd() returns NULL for all PMCs in that case, i.e. KVM already
violates AMD's architecture by not virtualizing a PMU (kernels have long
since learned to not panic when the PMU is unavailable). But configuring
the PMU as if it were enabled causes unwanted side effects, e.g. calls to
kvm_pmu_trigger_event() waste an absurd number of cycles due to the
all_valid_pmc_idx bitmap being non-zero.

Fixes: b1d66dad65dc ("KVM: x86/svm: Add module param to control PMU virtualization")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Closes: https://lore.kernel.org/all/20231109180646.2963718-2-khorenko@virtuozzo.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/pmu.c | 20 ++++++++++++++++++--
arch/x86/kvm/vmx/pmu_intel.c | 16 ++--------------
2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 1b74a29ed250..b52bab7dc422 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -739,6 +739,8 @@ static void kvm_pmu_reset(struct kvm_vcpu *vcpu)
*/
void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
{
+ struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
+
if (KVM_BUG_ON(kvm_vcpu_has_run(vcpu), vcpu->kvm))
return;

@@ -748,8 +750,22 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
*/
kvm_pmu_reset(vcpu);

- bitmap_zero(vcpu_to_pmu(vcpu)->all_valid_pmc_idx, X86_PMC_IDX_MAX);
- static_call(kvm_x86_pmu_refresh)(vcpu);
+ pmu->version = 0;
+ pmu->nr_arch_gp_counters = 0;
+ pmu->nr_arch_fixed_counters = 0;
+ pmu->counter_bitmask[KVM_PMC_GP] = 0;
+ pmu->counter_bitmask[KVM_PMC_FIXED] = 0;
+ pmu->reserved_bits = 0xffffffff00200000ull;
+ pmu->raw_event_mask = X86_RAW_EVENT_MASK;
+ pmu->global_ctrl_mask = ~0ull;
+ pmu->global_status_mask = ~0ull;
+ pmu->fixed_ctr_ctrl_mask = ~0ull;
+ pmu->pebs_enable_mask = ~0ull;
+ pmu->pebs_data_cfg_mask = ~0ull;
+ bitmap_zero(pmu->all_valid_pmc_idx, X86_PMC_IDX_MAX);
+
+ if (vcpu->kvm->arch.enable_pmu)
+ static_call(kvm_x86_pmu_refresh)(vcpu);
}

void kvm_pmu_init(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index c3a841d8df27..0d2fd9fdcf4b 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -463,19 +463,6 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
u64 counter_mask;
int i;

- pmu->nr_arch_gp_counters = 0;
- pmu->nr_arch_fixed_counters = 0;
- pmu->counter_bitmask[KVM_PMC_GP] = 0;
- pmu->counter_bitmask[KVM_PMC_FIXED] = 0;
- pmu->version = 0;
- pmu->reserved_bits = 0xffffffff00200000ull;
- pmu->raw_event_mask = X86_RAW_EVENT_MASK;
- pmu->global_ctrl_mask = ~0ull;
- pmu->global_status_mask = ~0ull;
- pmu->fixed_ctr_ctrl_mask = ~0ull;
- pmu->pebs_enable_mask = ~0ull;
- pmu->pebs_data_cfg_mask = ~0ull;
-
memset(&lbr_desc->records, 0, sizeof(lbr_desc->records));

/*
@@ -487,8 +474,9 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
return;

entry = kvm_find_cpuid_entry(vcpu, 0xa);
- if (!entry || !vcpu->kvm->arch.enable_pmu)
+ if (!entry)
return;
+
eax.full = entry->eax;
edx.full = entry->edx;

--
2.42.0.869.gea05f2083d-goog