linux-kernel - [PATCH v2 13/21] KVM: x86: Formalize blocking of nested pending exceptions

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Date:   Tue, 14 Jun 2022 20:47:22 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: [PATCH v2 13/21] KVM: x86: Formalize blocking of nested pending exceptions

Capture nested_run_pending as block_pending_exceptions so that the logic
of why exceptions are blocked only needs to be documented once instead of
at every place that employs the logic.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 20 ++++++++++----------
 arch/x86/kvm/vmx/nested.c | 23 ++++++++++++-----------
 2 files changed, 22 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 471d40e97890..460161e67ce5 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1347,10 +1347,16 @@ static inline bool nested_exit_on_init(struct vcpu_svm *svm)
 
 static int svm_check_nested_events(struct kvm_vcpu *vcpu)
 {
-	struct vcpu_svm *svm = to_svm(vcpu);
-	bool block_nested_events =
-		kvm_event_needs_reinjection(vcpu) || svm->nested.nested_run_pending;
 	struct kvm_lapic *apic = vcpu->arch.apic;
+	struct vcpu_svm *svm = to_svm(vcpu);
+	/*
+	 * Only a pending nested run blocks a pending exception.  If there is a
+	 * previously injected event, the pending exception occurred while said
+	 * event was being delivered and thus needs to be handled.
+	 */
+	bool block_nested_exceptions = svm->nested.nested_run_pending;
+	bool block_nested_events = block_nested_exceptions ||
+				   kvm_event_needs_reinjection(vcpu);
 
 	if (lapic_in_kernel(vcpu) &&
 	    test_bit(KVM_APIC_INIT, &apic->pending_events)) {
@@ -1363,13 +1369,7 @@ static int svm_check_nested_events(struct kvm_vcpu *vcpu)
 	}
 
 	if (vcpu->arch.exception.pending) {
-		/*
-		 * Only a pending nested run can block a pending exception.
-		 * Otherwise an injected NMI/interrupt should either be
-		 * lost or delivered to the nested hypervisor in the EXITINTINFO
-		 * vmcb field, while delivering the pending exception.
-		 */
-		if (svm->nested.nested_run_pending)
+		if (block_nested_exceptions)
                         return -EBUSY;
 		if (!nested_exit_on_exception(svm))
 			return 0;
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index fafdcbfeca1f..50fe66f0cc1b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3903,11 +3903,17 @@ static bool nested_vmx_preemption_timer_pending(struct kvm_vcpu *vcpu)
 
 static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 {
-	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	unsigned long exit_qual;
-	bool block_nested_events =
-	    vmx->nested.nested_run_pending || kvm_event_needs_reinjection(vcpu);
 	struct kvm_lapic *apic = vcpu->arch.apic;
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	unsigned long exit_qual;
+	/*
+	 * Only a pending nested run blocks a pending exception.  If there is a
+	 * previously injected event, the pending exception occurred while said
+	 * event was being delivered and thus needs to be handled.
+	 */
+	bool block_nested_exceptions = vmx->nested.nested_run_pending;
+	bool block_nested_events = block_nested_exceptions ||
+				   kvm_event_needs_reinjection(vcpu);
 
 	if (lapic_in_kernel(vcpu) &&
 		test_bit(KVM_APIC_INIT, &apic->pending_events)) {
@@ -3941,15 +3947,10 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 	 * Process exceptions that are higher priority than Monitor Trap Flag:
 	 * fault-like exceptions, TSS T flag #DB (not emulated by KVM, but
 	 * could theoretically come in from userspace), and ICEBP (INT1).
-	 *
-	 * Note that only a pending nested run can block a pending exception.
-	 * Otherwise an injected NMI/interrupt should either be
-	 * lost or delivered to the nested hypervisor in the IDT_VECTORING_INFO,
-	 * while delivering the pending exception.
 	 */
 	if (vcpu->arch.exception.pending &&
 	    !(vmx_get_pending_dbg_trap(vcpu) & ~DR6_BT)) {
-		if (vmx->nested.nested_run_pending)
+		if (block_nested_exceptions)
 			return -EBUSY;
 		if (!nested_vmx_check_exception(vcpu, &exit_qual))
 			goto no_vmexit;
@@ -3966,7 +3967,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 	}
 
 	if (vcpu->arch.exception.pending) {
-		if (vmx->nested.nested_run_pending)
+		if (block_nested_exceptions)
 			return -EBUSY;
 		if (!nested_vmx_check_exception(vcpu, &exit_qual))
 			goto no_vmexit;
-- 
2.36.1.476.g0c4daa206d-goog