On 3/9/22 17:46, Sasha Levin wrote:

From: Li RongQing lirongqing@baidu.com

[ Upstream commit 9ee83635d872812f3920209c606c6ea9e412ffcc ]

When sending a call-function IPI-many to vCPUs, yield to the IPI target vCPU which is marked as preempted.

but when emulating HLT, an idling vCPU will be voluntarily scheduled out and mark as preempted from the guest kernel perspective. yielding to idle vCPU is pointless and increase unnecessary vmexit, maybe miss the true preempted vCPU

so yield to IPI target vCPU only if vCPU is busy and preempted

Signed-off-by: Li RongQing lirongqing@baidu.com Message-Id: 1644380201-29423-1-git-send-email-lirongqing@baidu.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org

---

arch/x86/kernel/kvm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 59abbdad7729..2121c20e877f 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -619,7 +619,7 @@ static void kvm_smp_send_call_func_ipi(const struct cpumask *mask) /* Make sure other vCPUs get a chance to run if they need to. */ for_each_cpu(cpu, mask) {

• if (vcpu_is_preempted(cpu)) {
  

• if (!idle_cpu(cpu) && vcpu_is_preempted(cpu)) {
  kvm_hypercall1(KVM_HC_SCHED_YIELD, per_cpu(x86_cpu_to_apicid, cpu));
  break;
  

  }

NACK, just an optimization.

Paolo