linux-kernel - [PATCH] KVM: x86: Add a vCPU stat for #AC exceptions

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Message-ID: <20230426082601.85372-1-abusse@amazon.com>
Date:   Wed, 26 Apr 2023 08:26:01 +0000
From:   Anselm Busse <abusse@...zon.com>
To:     unlisted-recipients:; (no To-header on input)
CC:     <dwmw@...zon.co.uk>, <hborghor@...zon.de>, <sironi@...zon.de>,
        "Anselm Busse" <abusse@...zon.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] KVM: x86: Add a vCPU stat for #AC exceptions

This patch adds a KVM vCPU stat that reflects the number of #AC
exceptions caused by a guest. This improves the identification and
debugging of issues that are possibly caused by guests triggering
split-locks and allows more insides compared to the current situation
of having only a warning printed when an #AC exception is raised.

Signed-off-by: Anselm Busse <abusse@...zon.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/vmx/vmx.c          | 2 ++
 arch/x86/kvm/x86.c              | 1 +
 3 files changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 808c292ad3f4..b4ab719fbc69 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1523,6 +1523,7 @@ struct kvm_vcpu_stat {
 	u64 preemption_other;
 	u64 guest_mode;
 	u64 notify_window_exits;
+	u64 split_lock_exceptions;
 };
 
 struct x86_instruction_info;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d2d6e1b6c788..8f48fd8ddead 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5309,6 +5309,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 		kvm_run->debug.arch.exception = ex_no;
 		break;
 	case AC_VECTOR:
+		vmx->vcpu.stat.split_lock_exceptions++;
+
 		if (vmx_guest_inject_ac(vcpu)) {
 			kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
 			return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3d852ce84920..416a1ed6c423 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -297,6 +297,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
 	STATS_DESC_COUNTER(VCPU, preemption_other),
 	STATS_DESC_IBOOLEAN(VCPU, guest_mode),
 	STATS_DESC_COUNTER(VCPU, notify_window_exits),
+	STATS_DESC_COUNTER(VCPU, split_lock_exceptions),
 };
 
 const struct kvm_stats_header kvm_vcpu_stats_header = {
-- 
2.39.2




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