[RFC PATCH 11/41] KVM: x86/pmu: Introduce enable_passthrough_pmu module parameter and propage to KVM instance

[Xiong Zhang]

From: Mingwei Zhang <mizhang@xxxxxxxxxx>

Introduce enable_passthrough_pmu as a RO KVM kernel module parameter. This
variable is true only when the following conditions satisfies:
 - set to true when module loaded.
 - enable_pmu is true.
 - is running on Intel CPU.
 - supports PerfMon v4.
 - host PMU supports passthrough mode.

The value is always read-only because passthrough PMU currently does not
support features like LBR and PEBS, while emualted PMU does. This will end
up with two different values for kvm_cap.supported_perf_cap, which is
initialized at module load time. Maintaining two different perf
capabilities will add complexity. Further, there is not enough motivation
to support running two types of PMU implementations at the same time,
although it is possible/feasible in reality.

Finally, always propagate enable_passthrough_pmu and perf_capabilities into
kvm->arch for each KVM instance.

Co-developed-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/pmu.h              | 14 ++++++++++++++
 arch/x86/kvm/vmx/vmx.c          |  5 +++--
 arch/x86/kvm/x86.c              |  9 +++++++++
 arch/x86/kvm/x86.h              |  1 +
 5 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d7036982332e..f2e73e6830a3 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1371,6 +1371,7 @@ struct kvm_arch {
 
 	bool bus_lock_detection_enabled;
 	bool enable_pmu;
+	bool enable_passthrough_pmu;
 
 	u32 notify_window;
 	u32 notify_vmexit_flags;
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 1d64113de488..51011603c799 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -208,6 +208,20 @@ static inline void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops)
 			enable_pmu = false;
 	}
 
+	/* Pass-through vPMU is only supported in Intel CPUs. */
+	if (!is_intel)
+		enable_passthrough_pmu = false;
+
+	/*
+	 * Pass-through vPMU requires at least PerfMon version 4 because the
+	 * implementation requires the usage of MSR_CORE_PERF_GLOBAL_STATUS_SET
+	 * for counter emulation as well as PMU context switch.  In addition, it
+	 * requires host PMU support on passthrough mode. Disable pass-through
+	 * vPMU if any condition fails.
+	 */
+	if (!enable_pmu || kvm_pmu_cap.version < 4 || !kvm_pmu_cap.passthrough)
+		enable_passthrough_pmu = false;
+
 	if (!enable_pmu) {
 		memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
 		return;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index be20a60047b1..e4610b80e519 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7835,13 +7835,14 @@ static u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
 
-	if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) {
+	if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR) &&
+	    !enable_passthrough_pmu) {
 		x86_perf_get_lbr(&lbr);
 		if (lbr.nr)
 			perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
 	}
 
-	if (vmx_pebs_supported()) {
+	if (vmx_pebs_supported() && !enable_passthrough_pmu) {
 		perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
 		if ((perf_cap & PERF_CAP_PEBS_FORMAT) < 4)
 			perf_cap &= ~PERF_CAP_PEBS_BASELINE;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4432e736129f..074452aa700d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -193,6 +193,11 @@ bool __read_mostly enable_pmu = true;
 EXPORT_SYMBOL_GPL(enable_pmu);
 module_param(enable_pmu, bool, 0444);
 
+/* Enable/disable PMU virtualization */
+bool __read_mostly enable_passthrough_pmu = true;
+EXPORT_SYMBOL_GPL(enable_passthrough_pmu);
+module_param(enable_passthrough_pmu, bool, 0444);
+
 bool __read_mostly eager_page_split = true;
 module_param(eager_page_split, bool, 0644);
 
@@ -6553,6 +6558,9 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		mutex_lock(&kvm->lock);
 		if (!kvm->created_vcpus) {
 			kvm->arch.enable_pmu = !(cap->args[0] & KVM_PMU_CAP_DISABLE);
+			/* Disable passthrough PMU if enable_pmu is false. */
+			if (!kvm->arch.enable_pmu)
+				kvm->arch.enable_passthrough_pmu = false;
 			r = 0;
 		}
 		mutex_unlock(&kvm->lock);
@@ -12480,6 +12488,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	kvm->arch.default_tsc_khz = max_tsc_khz ? : tsc_khz;
 	kvm->arch.guest_can_read_msr_platform_info = true;
 	kvm->arch.enable_pmu = enable_pmu;
+	kvm->arch.enable_passthrough_pmu = enable_passthrough_pmu;
 
 #if IS_ENABLED(CONFIG_HYPERV)
 	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 5184fde1dc54..38b73e98eae9 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -329,6 +329,7 @@ extern u64 host_arch_capabilities;
 extern struct kvm_caps kvm_caps;
 
 extern bool enable_pmu;
+extern bool enable_passthrough_pmu;
 
 /*
  * Get a filtered version of KVM's supported XCR0 that strips out dynamic
-- 
2.34.1