[PATCH v3 3/5] KVM: x86: Fix misleading comments on handling pending exceptions

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The reason that exception.pending should block re-injection of
NMI/interrupt is not described correctly in comment in code.
Instead, it describes why a pending exception should be injected
before a pending NMI/interrupt.

Therefore, move currently present comment to code-block evaluating
a new pending event which explains why exception.pending is evaluated
first.
In addition, create a new comment describing that exception.pending
blocks re-injection of NMI/interrupt because the exception was
queued by handling vmexit which was due to NMI/interrupt delivery.

Fixes: 664f8e26b00c ("KVM: X86: Fix loss of exception which has not
yet been injected")

Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxx>
---
 arch/x86/kvm/x86.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9f6b45f2382a..f5587998b57a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6645,8 +6645,9 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
 	}
 
 	/*
-	 * Exceptions must be injected immediately, or the exception
-	 * frame will have the address of the NMI or interrupt handler.
+	 * NMI/interrupt must not be injected if an exception is
+	 * pending, because the exception was queued by handling
+	 * vmexit which was due to NMI/interrupt delivery.
 	 */
 	if (!vcpu->arch.exception.pending) {
 		if (vcpu->arch.nmi_injected) {
@@ -6667,6 +6668,12 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
 	}
 
 	/* try to inject new event if pending */
+
+	/*
+	 * Exception must be injected before NMI/interrupt,
+	 * otherwise the exception frame will have the address of the
+	 * NMI or interrupt handler.
+	 */
 	if (vcpu->arch.exception.pending) {
 		trace_kvm_inj_exception(vcpu->arch.exception.nr,
 					vcpu->arch.exception.has_error_code,
-- 
1.9.1




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