linux-kernel - [PATCH v4 13/24] KVM: x86: Formalize blocking of nested pending exceptions

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Message-Id: <20220723005137.1649592-14-seanjc@google.com>
Date:   Sat, 23 Jul 2022 00:51:26 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: [PATCH v4 13/24] 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>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/nested.c | 26 ++++++++++++++++----------
 arch/x86/kvm/vmx/nested.c | 29 ++++++++++++++++++-----------
 2 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 8f991592d277..a6111392985c 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1356,10 +1356,22 @@ 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;
+	/*
+	 * New events (not exceptions) are only recognized at instruction
+	 * boundaries.  If an event needs reinjection, then KVM is handling a
+	 * VM-Exit that occurred _during_ instruction execution; new events are
+	 * blocked until the instruction completes.
+	 */
+	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)) {
@@ -1372,13 +1384,7 @@ 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 0f5a7aec82a2..361c788a73d5 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3899,11 +3899,23 @@ 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;
+	/*
+	 * New events (not exceptions) are only recognized at instruction
+	 * boundaries.  If an event needs reinjection, then KVM is handling a
+	 * VM-Exit that occurred _during_ instruction execution; new events are
+	 * blocked until the instruction completes.
+	 */
+	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)) {
@@ -3942,15 +3954,10 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 	 * for TSS T flag #DBs).  KVM also doesn't save/restore pending MTF
 	 * across SMI/RSM as it should; that needs to be addressed in order to
 	 * prioritize SMI over MTF and trap-like #DBs.
-	 *
-	 * 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;
@@ -3967,7 +3974,7 @@ 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;
-- 
2.37.1.359.gd136c6c3e2-goog