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Message-ID: <63493d06-0b6c-9993-2315-64033dd041d6@redhat.com>
Date: Wed, 9 Mar 2022 17:47:35 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Cc: Li RongQing <lirongqing@...du.com>, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH MANUALSEL 5.15] KVM: x86: Yield to IPI target vCPU only if
it is busy
On 3/9/22 17:46, Sasha Levin wrote:
> From: Li RongQing <lirongqing@...du.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@...du.com>
> Message-Id: <1644380201-29423-1-git-send-email-lirongqing@...du.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.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 b656456c3a94..49f19e572a25 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -565,7 +565,7 @@ 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
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