[PATCH] KVM: x86: Drop redundant call to kvm_deliver_exception_payload()

[Yosry Ahmed]

In kvm_check_and_inject_events(), kvm_deliver_exception_payload() is
called for pending #DB exceptions. However, shortly after, the
per-vendor inject_exception callbacks are made. Both
vmx_inject_exception() and svm_inject_exception() unconditionally call
kvm_deliver_exception_payload(), so the call in
kvm_check_and_inject_events() is redundant.

Note that the extra call for pending #DB exceptions is harmless, as
kvm_deliver_exception_payload() clears exception.has_payload after the
first call.

The call in kvm_check_and_inject_events() was added in commit
f10c729ff965 ("kvm: vmx: Defer setting of DR6 until #DB delivery"). At
that point, the call was likely needed because svm_queue_exception()
checked whether an exception for L2 is intercepted by L1 before calling
kvm_deliver_exception_payload(), as SVM did not have a
check_nested_events callback. Since DR6 is updated before the #DB
intercept in SVM (unlike VMX), it was necessary to deliver the DR6
payload before calling svm_queue_exception().

After that, commit 7c86663b68ba ("KVM: nSVM: inject exceptions via
svm_check_nested_events") added a check_nested_events callback for SVM,
which checked for L1 intercepts for L2's exceptions, and delivered the
the payload appropriately before the intercept. At that point,
svm_queue_exception() started calling kvm_deliver_exception_payload()
unconditionally, and the call to kvm_deliver_exception_payload() from
its caller became redundant.

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db3f393192d94..a9080418f3cfd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10737,12 +10737,10 @@ static int kvm_check_and_inject_events(struct kvm_vcpu *vcpu,
 			__kvm_set_rflags(vcpu, kvm_get_rflags(vcpu) |
 					     X86_EFLAGS_RF);
 
-		if (vcpu->arch.exception.vector == DB_VECTOR) {
-			kvm_deliver_exception_payload(vcpu, &vcpu->arch.exception);
-			if (vcpu->arch.dr7 & DR7_GD) {
-				vcpu->arch.dr7 &= ~DR7_GD;
-				kvm_update_dr7(vcpu);
-			}
+		if (vcpu->arch.exception.vector == DB_VECTOR &&
+		    vcpu->arch.dr7 & DR7_GD) {
+			vcpu->arch.dr7 &= ~DR7_GD;
+			kvm_update_dr7(vcpu);
 		}
 
 		kvm_inject_exception(vcpu);

base-commit: 183bb0ce8c77b0fd1fb25874112bc8751a461e49
-- 
2.53.0.473.g4a7958ca14-goog