linux-kernel - [PATCH 4/4] KVM: x86: Add vCPU stat for APICv interrupt injections causing #VMEXIT

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Date: Mon, 29 Apr 2024 15:57:38 +0000
From: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To: kvm@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        suravee.suthikulpanit@....com, vashegde@....com, mlevitsk@...hat.com,
        joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
        mark.kanda@...cle.com, alejandro.j.jimenez@...cle.com
Subject: [PATCH 4/4] KVM: x86: Add vCPU stat for APICv interrupt injections causing #VMEXIT

Even when APICv/AVIC is active, certain guest accesses to its local APIC(s)
cannot be fully accelerated, and cause a #VMEXIT to allow the VMM to
emulate the behavior and side effects. Expose a counter stat for these
specific #VMEXIT types.

Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/svm/avic.c         | 7 +++++++
 arch/x86/kvm/vmx/vmx.c          | 2 ++
 arch/x86/kvm/x86.c              | 1 +
 4 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e7e3213cefae..388979dfe9f3 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1576,6 +1576,7 @@ struct kvm_vcpu_stat {
 	u64 guest_mode;
 	u64 notify_window_exits;
 	u64 apicv_active;
+	u64 apicv_unaccelerated_inj;
 };
 
 struct x86_instruction_info;
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 4b74ea91f4e6..274041d3cf66 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -517,6 +517,8 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
 			kvm_apic_write_nodecode(vcpu, APIC_ICR);
 		else
 			kvm_apic_send_ipi(apic, icrl, icrh);
+
+		++vcpu->stat.apicv_unaccelerated_inj;
 		break;
 	case AVIC_IPI_FAILURE_TARGET_NOT_RUNNING:
 		/*
@@ -525,6 +527,8 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
 		 * vcpus. So, we just need to kick the appropriate vcpu.
 		 */
 		avic_kick_target_vcpus(vcpu->kvm, apic, icrl, icrh, index);
+
+		++vcpu->stat.apicv_unaccelerated_inj;
 		break;
 	case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
 		WARN_ONCE(1, "Invalid backing page\n");
@@ -704,6 +708,9 @@ int avic_unaccelerated_access_interception(struct kvm_vcpu *vcpu)
 
 	trace_kvm_avic_unaccelerated_access(vcpu->vcpu_id, offset,
 					    trap, write, vector);
+
+	++vcpu->stat.apicv_unaccelerated_inj;
+
 	if (trap) {
 		/* Handling Trap */
 		WARN_ONCE(!write, "svm: Handling trap read.\n");
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f10b5f8f364b..a7487f12ded1 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5657,6 +5657,8 @@ static int handle_apic_write(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
 
+	++vcpu->stat.apicv_unaccelerated_inj;
+
 	/*
 	 * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
 	 * hardware has done any necessary aliasing, offset adjustments, etc...
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 03cb933920cb..c8730b0fac87 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -307,6 +307,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
 	STATS_DESC_IBOOLEAN(VCPU, guest_mode),
 	STATS_DESC_COUNTER(VCPU, notify_window_exits),
 	STATS_DESC_IBOOLEAN(VCPU, apicv_active),
+	STATS_DESC_COUNTER(VCPU, apicv_unaccelerated_inj),
 };
 
 const struct kvm_stats_header kvm_vcpu_stats_header = {
-- 
2.39.3