linux-kernel - [PATCH v2] KVM: x86/pmu: Disable all vPMU features support on Intel hybrid CPUs

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Message-Id: <20230131085031.88939-1-likexu@tencent.com>
Date:   Tue, 31 Jan 2023 16:50:31 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jianfeng Gao <jianfeng.gao@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2] KVM: x86/pmu: Disable all vPMU features support on Intel hybrid CPUs

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

Disable KVM support for virtualizing PMUs on hosts with hybrid PMUs until
KVM gains a sane way to enumeration the hybrid vPMU to userspace and/or
gains a mechanism to let userspace opt-in to the dangers of exposing a
hybrid vPMU to KVM guests.

Virtualizing a hybrid PMU, or at least part of a hybrid PMU, is possible,
but it requires userspace to pin vCPUs to pCPUs to prevent migrating a
vCPU between a big core and a little core, requires the VMM to accurately
enumerate the topology to the guest (if exposing a hybrid CPU to the
guest), and also requires the VMM to accurately enumerate the vPMU
capabilities to the guest.

The last point is especially problematic, as KVM doesn't control which
pCPU it runs on when enumerating KVM's vPMU capabilities to userspace.
For now, simply disable vPMU support on hybrid CPUs to avoid inducing
seemingly random #GPs in guests.

Reported-by: Jianfeng Gao <jianfeng.gao@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Like Xu <likexu@...cent.com>
---
v1: https://lore.kernel.org/all/20230120004051.2043777-1-seanjc@google.com/
 arch/x86/kvm/pmu.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 79988dafb15b..6a3995657e1e 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -166,9 +166,11 @@ static inline void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops)

 	 /*
 	  * For Intel, only support guest architectural pmu
-	  * on a host with architectural pmu.
+	  * on a non-hybrid host with architectural pmu.
 	  */
-	if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp)
+	if (!kvm_pmu_cap.num_counters_gp ||
+	    (is_intel && (!kvm_pmu_cap.version ||
+			  boot_cpu_has(X86_FEATURE_HYBRID_CPU))))
 		enable_pmu = false;

 	if (!enable_pmu) {
-- 
2.39.1