From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Wed, 22 Apr 2020 19:25:38 -0700
Subject: KVM: nVMX: Preserve exception priority irrespective of exiting
 behavior
Git-commit: 6ce347af1499deff5890a52aedacd451330af706
Patch-mainline: v5.8-rc1
References: bsc#1188777

Short circuit vmx_check_nested_events() if an exception is pending and
needs to be injected into L2, priority between coincident events is not
dependent on exiting behavior.  This fixes a bug where a single-step #DB
that is not intercepted by L1 is incorrectly dropped due to servicing a
VMX Preemption Timer VM-Exit.

Injected exceptions also need to be blocked if nested VM-Enter is
pending or an exception was already injected, otherwise injecting the
exception could overwrite an existing event injection from L1.
Technically, this scenario should be impossible, i.e. KVM shouldn't
inject its own exception during nested VM-Enter.  This will be addressed
in a future patch.

Note, event priority between SMI, NMI and INTR is incorrect for L2, e.g.
SMI should take priority over VM-Exit on NMI/INTR, and NMI that is
injected into L2 should take priority over VM-Exit INTR.  This will also
be addressed in a future patch.

Fixes: b6b8a1451fc4 ("KVM: nVMX: Rework interception of IRQs and NMIs")
Reported-by: Jim Mattson <jmattson@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Peter Shier <pshier@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200423022550.15113-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
---
 arch/x86/kvm/vmx/nested.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index bd96be3ca456..f047940c1795 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3455,11 +3455,11 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool __unused)
 	/*
 	 * Process any exceptions that are not debug traps before MTF.
 	 */
-	if (vcpu->arch.exception.pending &&
-	    !vmx_pending_dbg_trap(vcpu) &&
-	    nested_vmx_check_exception(vcpu, &exit_qual)) {
+	if (vcpu->arch.exception.pending && !vmx_pending_dbg_trap(vcpu)) {
 		if (block_nested_events)
 			return -EBUSY;
+		if (!nested_vmx_check_exception(vcpu, &exit_qual))
+			goto no_vmexit;
 		nested_vmx_inject_exception_vmexit(vcpu, exit_qual);
 		return 0;
 	}
@@ -3472,10 +3472,11 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool __unused)
 		return 0;
 	}
 
-	if (vcpu->arch.exception.pending &&
-	    nested_vmx_check_exception(vcpu, &exit_qual)) {
+	if (vcpu->arch.exception.pending) {
 		if (block_nested_events)
 			return -EBUSY;
+		if (!nested_vmx_check_exception(vcpu, &exit_qual))
+			goto no_vmexit;
 		nested_vmx_inject_exception_vmexit(vcpu, exit_qual);
 		return 0;
 	}
@@ -3510,6 +3511,7 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool __unused)
 		return 0;
 	}
 
+no_vmexit:
 	vmx_complete_nested_posted_interrupt(vcpu);
 	return 0;
 }
-- 
2.32.0