[PATCH v3] KVM: x86: Make the module parameter of vPMU more common

[Like Xu]

From: Like Xu <likexu@xxxxxxxxxxx>

The new module parameter to control PMU virtualization should apply
to Intel as well as AMD, for situations where userspace is not trusted.
If the module parameter allows PMU virtualization, there could be a
new KVM_CAP or guest CPUID bits whereby userspace can enable/disable
PMU virtualization on a per-VM basis.

If the module parameter does not allow PMU virtualization, there
should be no userspace override, since we have no precedent for
authorizing that kind of override. If it's false, other counter-based
profiling features (such as LBR including the associated CPUID bits
if any) will not be exposed.

The module_param_named() is used so that KVM can use "enable_pmu"
for all its checks, but the user only needs to type "pmu=?" when
manipulating the module param.

Fixes: b1d66dad65dc ("KVM: x86/svm: Add module param to control PMU virtualization")
Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
v2 -> v3 Changelog:
- Use module_param_named() for the use of both enable_pmu and pmu; (Sean)

Previous:
https://lore.kernel.org/kvm/20220112040116.23937-1-likexu@xxxxxxxxxxx/

 arch/x86/kvm/cpuid.c            | 6 +++---
 arch/x86/kvm/pmu.c              | 5 +++++
 arch/x86/kvm/pmu.h              | 1 +
 arch/x86/kvm/svm/pmu.c          | 2 +-
 arch/x86/kvm/svm/svm.c          | 8 ++------
 arch/x86/kvm/svm/svm.h          | 1 -
 arch/x86/kvm/vmx/capabilities.h | 4 ++++
 arch/x86/kvm/vmx/pmu_intel.c    | 2 +-
 8 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0b920e12bb6d..4ac7172478a0 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -770,10 +770,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		perf_get_x86_pmu_capability(&cap);
 
 		/*
-		 * Only support guest architectural pmu on a host
-		 * with architectural pmu.
+		 * The guest architecture pmu is only supported if the architecture
+		 * pmu exists on the host and the module parameters allow it.
 		 */
-		if (!cap.version)
+		if (!enable_pmu || !cap.version)
 			memset(&cap, 0, sizeof(cap));
 
 		eax.split.version_id = min(cap.version, 2);
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index e632693a2266..03e6a24dd8cb 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -19,6 +19,11 @@
 #include "lapic.h"
 #include "pmu.h"
 
+/* Enable/disable PMU virtualization */
+bool __read_mostly enable_pmu = true;
+EXPORT_SYMBOL_GPL(enable_pmu);
+module_param_named(pmu, enable_pmu, bool, 0444);
+
 /* This is enough to filter the vast majority of currently defined events. */
 #define KVM_PMU_EVENT_FILTER_MAX_EVENTS 300
 
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 7a7b8d5b775e..46df3d58784b 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -163,4 +163,5 @@ 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 bool enable_pmu;
 #endif /* __KVM_X86_PMU_H */
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 12d8b301065a..5aa45f13b16d 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -101,7 +101,7 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
 {
 	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
 
-	if (!pmu)
+	if (!enable_pmu)
 		return NULL;
 
 	switch (msr) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 6cb38044a860..549f73ce5ebc 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -192,10 +192,6 @@ module_param(vgif, int, 0444);
 static int lbrv = true;
 module_param(lbrv, int, 0444);
 
-/* enable/disable PMU virtualization */
-bool pmu = true;
-module_param(pmu, bool, 0444);
-
 static int tsc_scaling = true;
 module_param(tsc_scaling, int, 0444);
 
@@ -4573,7 +4569,7 @@ static __init void svm_set_cpu_caps(void)
 		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
 
 	/* AMD PMU PERFCTR_CORE CPUID */
-	if (pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
+	if (enable_pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
 		kvm_cpu_cap_set(X86_FEATURE_PERFCTR_CORE);
 
 	/* CPUID 0x8000001F (SME/SEV features) */
@@ -4712,7 +4708,7 @@ static __init int svm_hardware_setup(void)
 			pr_info("LBR virtualization supported\n");
 	}
 
-	if (!pmu)
+	if (!enable_pmu)
 		pr_info("PMU virtualization is disabled\n");
 
 	svm_set_cpu_caps();
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index daa8ca84afcc..47ef8f4a9358 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -32,7 +32,6 @@
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
 extern bool intercept_smi;
-extern bool pmu;
 
 /*
  * Clean bits in VMCB.
diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index c8029b7845b6..401c48000a48 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -5,6 +5,7 @@
 #include <asm/vmx.h>
 
 #include "lapic.h"
+#include "pmu.h"
 
 extern bool __read_mostly enable_vpid;
 extern bool __read_mostly flexpriority_enabled;
@@ -389,6 +390,9 @@ static inline u64 vmx_get_perf_capabilities(void)
 {
 	u64 perf_cap = 0;
 
+	if (!enable_pmu)
+		return perf_cap;
+
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
 
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index ffccfd9823c0..f3656b95cd2f 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -487,7 +487,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 	pmu->reserved_bits = 0xffffffff00200000ull;
 
 	entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
-	if (!entry)
+	if (!enable_pmu || !entry)
 		return;
 	eax.full = entry->eax;
 	edx.full = entry->edx;
-- 
2.33.1