[PATCH] kvm: Simplify kvm_get_running_vcpu()

From: Lai Jiangshan
Date: Thu Jun 20 2024 - 04:08:47 EST


From: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>

this_cpu_read() is exactly the same behavior as "preempt_disable() +
__this_cpu_read() + preempt_enable()", and it uses less instructions
in X86.

Just use this_cpu_read() to simplify kvm_get_running_vcpu().

Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Link: https://lore.kernel.org/kvm/20200207163410.31276-1-maz@xxxxxxxxxx/
Signed-off-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
---
virt/kvm/kvm_main.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 14841acb8b95..0d18e9b1017f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -6306,21 +6306,14 @@ static void kvm_sched_out(struct preempt_notifier *pn,
/**
* kvm_get_running_vcpu - get the vcpu running on the current CPU.
*
- * We can disable preemption locally around accessing the per-CPU variable,
- * and use the resolved vcpu pointer after enabling preemption again,
+ * The result is either NULL or the vcpu running on the current thread
* because even if the current thread is migrated to another CPU, reading
* the per-CPU value later will give us the same value as we update the
* per-CPU variable in the preempt notifier handlers.
*/
struct kvm_vcpu *kvm_get_running_vcpu(void)
{
- struct kvm_vcpu *vcpu;
-
- preempt_disable();
- vcpu = __this_cpu_read(kvm_running_vcpu);
- preempt_enable();
-
- return vcpu;
+ return this_cpu_read(kvm_running_vcpu);
}
EXPORT_SYMBOL_GPL(kvm_get_running_vcpu);

--
2.19.1.6.gb485710b