linux-kernel - [PATCH] KVM: nVMX: Track vmx emulation errors

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Message-ID: <20260120144550.1083396-1-griffoul@gmail.com>
Date: Tue, 20 Jan 2026 14:45:50 +0000
From: Fred Griffoul <griffoul@...il.com>
To: kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	pbonzini@...hat.com,
	linux-kernel@...r.kernel.org,
	Fred Griffoul <fgriffo@...zon.co.uk>
Subject: [PATCH] KVM: nVMX: Track vmx emulation errors

From: Fred Griffoul <fgriffo@...zon.co.uk>

Add a new kvm_stat vcpu counter called "nested_errors" to track the
number of errors returned to an L1 hypervisor when emulated VMX
instructions fail.

This counter should help monitor nVMX health and troubleshoot issues
with L1 hypervisors.

Signed-off-by: Fred Griffoul <fgriffo@...zon.co.uk>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/vmx/nested.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 5a3bfa293e8b..a3aaccd6e6aa 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1674,6 +1674,7 @@ struct kvm_vcpu_stat {
 	u64 preemption_other;
 	u64 guest_mode;
 	u64 notify_window_exits;
+	u64 nested_errors;
 };
 
 struct x86_instruction_info;
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 6137e5307d0f..2e1394151945 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -162,6 +162,7 @@ static int nested_vmx_succeed(struct kvm_vcpu *vcpu)
 
 static int nested_vmx_failInvalid(struct kvm_vcpu *vcpu)
 {
+	++vcpu->stat.nested_errors;
 	vmx_set_rflags(vcpu, (vmx_get_rflags(vcpu)
 			& ~(X86_EFLAGS_PF | X86_EFLAGS_AF | X86_EFLAGS_ZF |
 			    X86_EFLAGS_SF | X86_EFLAGS_OF))
@@ -172,6 +173,7 @@ static int nested_vmx_failInvalid(struct kvm_vcpu *vcpu)
 static int nested_vmx_failValid(struct kvm_vcpu *vcpu,
 				u32 vm_instruction_error)
 {
+	++vcpu->stat.nested_errors;
 	vmx_set_rflags(vcpu, (vmx_get_rflags(vcpu)
 			& ~(X86_EFLAGS_CF | X86_EFLAGS_PF | X86_EFLAGS_AF |
 			    X86_EFLAGS_SF | X86_EFLAGS_OF))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ff8812f3a129..475c8a2d704e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -299,6 +299,7 @@ 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, nested_errors),
 };
 
 const struct kvm_stats_header kvm_vcpu_stats_header = {

base-commit: 0499add8efd72456514c6218c062911ccc922a99
-- 
2.43.0