[v2,19/54] KVM: x86/pmu: Add host_perf_cap and initialize it in kvm_x86_vendor_init()

Commit Message

Mingwei Zhang May 6, 2024, 5:29 a.m. UTC

Initialize host_perf_cap early in kvm_x86_vendor_init(). This helps KVM
recognize the HW PMU capability against its guest VMs.  This awareness
directly decides the feasibility of passing through RDPMC and indirectly
affects the performance in PMU context switch. Having the host PMU feature
set cached in host_perf_cap saves a rdmsrl() to IA32_PERF_CAPABILITY MSR on
each PMU context switch.

In addition, just opportunistically remove the host_perf_cap initialization
in vmx_get_perf_capabilities() so the value is not dependent on module
parameter "enable_pmu".

Signed-off-by: Mingwei Zhang <[e-mail]>
---
 arch/x86/kvm/pmu.h     | 1 +
 arch/x86/kvm/vmx/vmx.c | 4 ----
 arch/x86/kvm/x86.c     | 6 ++++++
 3 files changed, 7 insertions(+), 4 deletions(-)

Patch

diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 56ba0772568c..e041c8a23e2f 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -295,4 +295,5 @@  bool is_vmware_backdoor_pmc(u32 pmc_idx);
 
 extern struct kvm_pmu_ops intel_pmu_ops;
 extern struct kvm_pmu_ops amd_pmu_ops;
+extern u64 __read_mostly host_perf_cap;
 #endif /* __KVM_X86_PMU_H */
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index af253cfa5c37..a5024b7b0439 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7868,14 +7868,10 @@  static 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)
 		return 0;
 
-	if (boot_cpu_has(X86_FEATURE_PDCM))
-		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
-
 	if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR) &&
 	    !enable_passthrough_pmu) {
 		x86_perf_get_lbr(&lbr);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4c289fcb34fe..db395c00955f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -245,6 +245,9 @@  EXPORT_SYMBOL_GPL(host_xss);
 u64 __read_mostly host_arch_capabilities;
 EXPORT_SYMBOL_GPL(host_arch_capabilities);
 
+u64 __read_mostly host_perf_cap;
+EXPORT_SYMBOL_GPL(host_perf_cap);
+
 const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
 	KVM_GENERIC_VM_STATS(),
 	STATS_DESC_COUNTER(VM, mmu_shadow_zapped),
@@ -9772,6 +9775,9 @@  int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
 		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, host_arch_capabilities);
 
+	if (boot_cpu_has(X86_FEATURE_PDCM))
+		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
+
 	r = ops->hardware_setup();
 	if (r != 0)
 		goto out_mmu_exit;