linux-kernel - [PATCH v3 1/3] KVM: x86/pmu: Disable guest PEBS on hybird cpu due to heterogeneity

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Date:   Wed,  9 Nov 2022 16:28:00 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH v3 1/3] KVM: x86/pmu: Disable guest PEBS on hybird cpu due to heterogeneity

From: Like Xu <likexu@...cent.com>

>From vPMU enabling perspective, KVM does not have proper support for
hybird x86 core. The reported perf_capabilities value (e.g. the format
of pebs record) depends on the type of cpu the kvm-intel module is init.
When a vcpu of one pebs format migrates to a vcpu of another pebs format,
the incorrect parsing of pebs records by guest can make profiling data
analysis extremely problematic.

The safe way to fix this is to disable this part of the support until the
guest recognizes that it is running on the hybird cpu, which is appropriate
at the moment given that x86 hybrid architectures are not heavily touted
in the data center market.

Signed-off-by: Like Xu <likexu@...cent.com>
---
 arch/x86/kvm/vmx/capabilities.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index cd2ac9536c99..ea0498684048 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -392,7 +392,9 @@ static inline bool vmx_pt_mode_is_host_guest(void)
 
 static inline bool vmx_pebs_supported(void)
 {
-	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
+	return boot_cpu_has(X86_FEATURE_PEBS) &&
+	       !boot_cpu_has(X86_FEATURE_HYBRID_CPU) &&
+	       kvm_pmu_cap.pebs_ept;
 }
 
 static inline bool cpu_has_notify_vmexit(void)
-- 
2.38.1