linux-kernel - [PATCH] KVM: x86/pmu: Disable vPMU if EVENTSEL

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Message-Id: <20230307113819.34089-1-likexu@tencent.com>
Date:   Tue,  7 Mar 2023 19:38:19 +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
Subject: [PATCH] KVM: x86/pmu: Disable vPMU if EVENTSEL_GUESTONLY bit doesn't exist

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

Unlike Intel's msr atomic_switch mechanism, AMD supports guest pmu
basic counter feature by setting the GUESTONLY bit on the host, so the
presence or absence of this bit determines whether vPMU is emulatable
(e.g. in nested virtualization). Since on AMD, writing reserved bits of
EVENTSEL register does not bring #GP, KVM needs to update the global
enable_pmu value by checking the persistence of this GUESTONLY bit.

Signed-off-by: Like Xu <likexu@...cent.com>
---
 arch/x86/kvm/svm/svm.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index dd21e8b1a259..f41d96e638ef 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4866,6 +4866,16 @@ static __init void svm_adjust_mmio_mask(void)
 	kvm_mmu_set_mmio_spte_mask(mask, mask, PT_WRITABLE_MASK | PT_USER_MASK);
 }
 
+static __init bool pmu_has_guestonly_mode(void)
+{
+	u64 value;
+
+	wrmsrl(MSR_F15H_PERF_CTL0, AMD64_EVENTSEL_GUESTONLY);
+	rdmsrl(MSR_F15H_PERF_CTL0, value);
+
+	return value == AMD64_EVENTSEL_GUESTONLY;
+}
+
 static __init void svm_set_cpu_caps(void)
 {
 	kvm_set_cpu_caps();
@@ -4911,8 +4921,11 @@ static __init void svm_set_cpu_caps(void)
 		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
 
 	/* AMD PMU PERFCTR_CORE CPUID */
-	if (enable_pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
+	if (enable_pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE) &&
+	    pmu_has_guestonly_mode())
 		kvm_cpu_cap_set(X86_FEATURE_PERFCTR_CORE);
+	else
+		enable_pmu = false;
 
 	/* CPUID 0x8000001F (SME/SEV features) */
 	sev_set_cpu_caps();

base-commit: 13738a3647368f7f600b30d241779bcd2a3ebbfd
-- 
2.39.2