[PATCH 1/2] s390/kvm: Refactor __diag_time_slice_end_directed for single exit point

[Ciunas Bennett <ciunas@linux.ibm.com>]

Refactor the DIAG 9c (directed yield) handler to use a unified exit path,
improving code maintainability and reducing duplication.
Changes:
 - Consolidate all exit paths to use a single 'out' label
 - Replace multiple VCPU_EVENT logging calls with one unified call
 - Introduce 'result' string variable to track operation outcome
 - Initialize tcpu_cpu to -1 for safe handling across all code paths
 - Ensure statistics updates occur before the common exit point

This refactoring maintains identical functionality while making the control
flow clearer and easier to maintain. All three possible outcomes (yield
forwarded, done, ignored) now converge at a single logging point

Signed-off-by: Ciunas Bennett <ciunas@linux.ibm.com>
---
 arch/s390/kvm/diag.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index d89d1c381522..85c84421b510 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -186,7 +186,8 @@ static int diag9c_forwarding_overrun(void)
 static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
 {
 	struct kvm_vcpu *tcpu;
-	int tcpu_cpu;
+	const char *result;
+	int tcpu_cpu = -1;
 	int tid;
 
 	tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
@@ -211,21 +212,22 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
 		if (!vcpu_is_preempted(tcpu_cpu))
 			goto no_yield;
 		smp_yield_cpu(tcpu_cpu);
-		VCPU_EVENT(vcpu, 5,
-			   "diag time slice end directed to %d: yield forwarded",
-			   tid);
 		vcpu->stat.diag_9c_forward++;
-		return 0;
+		result = "yield forwarded";
+		goto out;
 	}
 
 	if (kvm_vcpu_yield_to(tcpu) <= 0)
 		goto no_yield;
 
-	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: done", tid);
-	return 0;
+	result = "done";
+	goto out;
 no_yield:
-	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: ignored", tid);
 	vcpu->stat.diag_9c_ignored++;
+	result = "ignored";
+out:
+	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: %s", tid,
+		   result);
 	return 0;
 }
 
-- 
2.54.0