linux-kernel - [PATCH 1/4] KVM: x86: pending exceptions must not be blocked by an injected event

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Date:   Thu,  1 Apr 2021 17:38:14 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT)), Vitaly Kuznetsov <vkuznets@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Ingo Molnar <mingo@...hat.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 1/4] KVM: x86: pending exceptions must not be blocked by an injected event

Injected interrupts/nmi should not block a pending exception,
but rather be either lost if nested hypervisor doesn't
intercept the pending exception (as in stock x86), or be delivered
in exitintinfo/IDT_VECTORING_INFO field, as a part of a VMexit
that corresponds to the pending exception.

The only reason for an exception to be blocked is when nested run
is pending (and that can't really happen currently
but still worth checking for).

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/nested.c |  8 +++++++-
 arch/x86/kvm/vmx/nested.c | 10 ++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 8523f60adb92..34a37b2bd486 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1062,7 +1062,13 @@ static int svm_check_nested_events(struct kvm_vcpu *vcpu)
 	}
 
 	if (vcpu->arch.exception.pending) {
-		if (block_nested_events)
+		/*
+		 * 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)
                         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 fd334e4aa6db..c3ba842fc07f 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3806,9 +3806,15 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 
 	/*
 	 * Process any exceptions that are not debug traps before MTF.
+	 *
+	 * 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_pending_dbg_trap(vcpu)) {
-		if (block_nested_events)
+		if (vmx->nested.nested_run_pending)
 			return -EBUSY;
 		if (!nested_vmx_check_exception(vcpu, &exit_qual))
 			goto no_vmexit;
@@ -3825,7 +3831,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu)
 	}
 
 	if (vcpu->arch.exception.pending) {
-		if (block_nested_events)
+		if (vmx->nested.nested_run_pending)
 			return -EBUSY;
 		if (!nested_vmx_check_exception(vcpu, &exit_qual))
 			goto no_vmexit;
-- 
2.26.2