[PATCH v3 17/18] KVM: x86/pmu: Advertise PerfMon version 5 on Intel hosts

[Zide Chen]

From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

KVM currently caps the guest PerfMon version at 2 for all Intel
platforms. Now that KVM emulates the basic architectural PMU features
introduced in PerfMon versions 3 through 5, raise the guest PerfMon
version to 5. Features that require additional emulation support, e.g.
architectural LBR will be enabled separately.

PerfMon versions 3 and 4 continue to be exposed as version 2 because
KVM cannot safely virtualize AnyThread due to cross-VM information
leakage. PerfMon v5 is supported because it provides the
AnyThread-deprecated capability, allowing KVM to indicate that
AnyThread is deprecated.

When enable_mediated_pmu is disabled or in the non-Intel paths, KVM
retains the existing cap of version 2.

Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
v3:
- Simplify version cap logic since mediated PMU already requires
  version >= 4. (Jim)
v2:
- Cap vPMU v3/v4 to v2, as AnyThread cannot be safely virtualized.
  (Sashiko)
---
 arch/x86/kvm/pmu.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index afb3e18a9879..f949fdbf359c 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -175,7 +175,17 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops)
 	}
 
 	memcpy(&kvm_pmu_cap, &kvm_host_pmu, sizeof(kvm_host_pmu));
-	kvm_pmu_cap.version = min(kvm_pmu_cap.version, 2);
+
+	/*
+	 * PMU v3/v4 has AnyThread support, which KVM cannot safely virtualize.
+	 * Only expose PMU v5+ for Intel mediated PMU, where AnyThread is
+	 * deprecated; otherwise, cap at PMU v2.
+	 */
+	if (is_intel && enable_mediated_pmu && kvm_pmu_cap.version >= 5)
+		kvm_pmu_cap.version = 5;
+	else
+		kvm_pmu_cap.version = min(kvm_pmu_cap.version, 2);
+
 	kvm_pmu_cap.cntr_mask64 &=
 		GENMASK_ULL(pmu_ops->MAX_NR_GP_COUNTERS - 1, 0);
 	kvm_pmu_cap.fixed_cntr_mask64 &=
-- 
2.56.0