[PATCH 1/3] KVM: VMX: Snapshot LBR capabilities during module initialization

Sean Christopherson
2024-03-07T01:13:49Z

Snapshot VMX's LBR capabilities once during module initialization instead
of calling into perf every time a vCPU reconfigures its vPMU. This will
allow massaging the LBR capabilities, e.g. if the CPU doesn't support
callstacks, without having to remember to update multiple locations.

Opportunistically tag vmx_get_perf_capabilities() with __init, as it's
only called from vmx_set_cpu_caps().

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/pmu_intel.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 9 +++++----
arch/x86/kvm/vmx/vmx.h | 2 ++
3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 12ade343a17e..be40474de6e4 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -535,7 +535,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
perf_capabilities = vcpu_get_perf_capabilities(vcpu);
if (cpuid_model_is_consistent(vcpu) &&
(perf_capabilities & PMU_CAP_LBR_FMT))
- x86_perf_get_lbr(&lbr_desc->records);
+ memcpy(&lbr_desc->records, &vmx_lbr_caps, sizeof(vmx_lbr_caps));
else
lbr_desc->records.nr = 0;

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7a74388f9ecf..2a7cd66988a5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -217,6 +217,8 @@ module_param(ple_window_max, uint, 0444);
int __read_mostly pt_mode = PT_MODE_SYSTEM;
module_param(pt_mode, int, S_IRUGO);

+struct x86_pmu_lbr __ro_after_init vmx_lbr_caps;
+
static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
static DEFINE_MUTEX(vmx_l1d_flush_mutex);
@@ -7844,10 +7846,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vmx_update_exception_bitmap(vcpu);
}

-static u64 vmx_get_perf_capabilities(void)
+static __init u64 vmx_get_perf_capabilities(void)
{
u64 perf_cap = PMU_CAP_FW_WRITES;
- struct x86_pmu_lbr lbr;
u64 host_perf_cap = 0;

if (!enable_pmu)
@@ -7857,8 +7858,8 @@ static u64 vmx_get_perf_capabilities(void)
rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);

if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) {
- x86_perf_get_lbr(&lbr);
- if (lbr.nr)
+ x86_perf_get_lbr(&vmx_lbr_caps);
+ if (vmx_lbr_caps.nr)
perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
}

diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 65786dbe7d60..cc10df53966e 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -109,6 +109,8 @@ struct lbr_desc {
bool msr_passthrough;
};

+extern struct x86_pmu_lbr vmx_lbr_caps;
+
/*
* The nested_vmx structure is part of vcpu_vmx, and holds information we need
* for correct emulation of VMX (i.e., nested VMX) on this vcpu.
--
2.44.0.278.ge034bb2e1d-goog