[PATCH v4 13/40] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

[Yury Norov <yury.norov@gmail.com>]

The function traverses stimer_pending_bitmap in a for-loop bit by bit.
Simplify it by using atomic for_each_test_and_clear_bit().

Because there are only 4 bits, using for_each_test_and_clear_bit() will
generate inline code, so no excessive bloating with the new API.

While here, refactor the logic by decreasing indentation level.

CC: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/hyperv.c | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 8a47f8541eab..96acbcf603f5 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -28,6 +28,7 @@
 #include "xen.h"
 
 #include <linux/cpu.h>
+#include <linux/find_atomic.h>
 #include <linux/kvm_host.h>
 #include <linux/highmem.h>
 #include <linux/sched/cputime.h>
@@ -870,27 +871,27 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
 	if (!hv_vcpu)
 		return;
 
-	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
-		if (test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap)) {
-			stimer = &hv_vcpu->stimer[i];
-			if (stimer->config.enable) {
-				exp_time = stimer->exp_time;
-
-				if (exp_time) {
-					time_now =
-						get_time_ref_counter(vcpu->kvm);
-					if (time_now >= exp_time)
-						stimer_expiration(stimer);
-				}
-
-				if ((stimer->config.enable) &&
-				    stimer->count) {
-					if (!stimer->msg_pending)
-						stimer_start(stimer);
-				} else
-					stimer_cleanup(stimer);
-			}
+	for_each_test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap,
+				    ARRAY_SIZE(hv_vcpu->stimer)) {
+		stimer = &hv_vcpu->stimer[i];
+		if (!stimer->config.enable)
+			continue;
+
+		exp_time = stimer->exp_time;
+
+		if (exp_time) {
+			time_now = get_time_ref_counter(vcpu->kvm);
+			if (time_now >= exp_time)
+				stimer_expiration(stimer);
 		}
+
+		if (stimer->config.enable && stimer->count) {
+			if (!stimer->msg_pending)
+				stimer_start(stimer);
+		} else {
+			stimer_cleanup(stimer);
+		}
+	}
 }
 
 void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)
-- 
2.43.0