[PATCH v2 6/8] KVM: x86: Fix misleading comments on handling pending exceptions

[Liran Alon <liran.alon@oracle.com>]

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 may have
been queued during handling of exit 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@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@orcle.com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@orcle.com>
---
 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 f4a623ba087e..a4b5a013064b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6404,8 +6404,9 @@ 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 latter may have been queued by
+	 * handling exit due to NMI/interrupt delivery.
 	 */
 	if (!vcpu->arch.exception.pending) {
 		if (vcpu->arch.nmi_injected) {
@@ -6426,6 +6427,12 @@ 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