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
