linux-kernel - Re: [PATCH v2] KVM: LAPIC: Enable timer posted-interrupt when mwait/hlt is advertised

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Date:   Wed, 12 Jan 2022 00:39:15 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Aili Yao <yaoaili@...gsoft.com>
Subject: Re: [PATCH v2] KVM: LAPIC: Enable timer posted-interrupt when
 mwait/hlt is advertised

On Thu, Jan 06, 2022, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> As commit 0c5f81dad46 (KVM: LAPIC: Inject timer interrupt via posted interrupt) 
> mentioned that the host admin should well tune the guest setup, so that vCPUs 
> are placed on isolated pCPUs, and with several pCPUs surplus for *busy* housekeeping.
> It is better to disable mwait/hlt/pause vmexits to keep the vCPUs in non-root 
> mode. However, we may isolate pCPUs for other purpose like DPDK or we can make 
> some guests isolated and others not, we may lose vmx preemption timer/timer fastpath 
> due to not well tuned setup, and the checking in kvm_can_post_timer_interrupt() 
> is not enough. Let's guarantee mwait/hlt is advertised before enabling posted-interrupt 
> interrupt. vmx preemption timer/timer fastpath can continue to work if both of them 
> are not advertised.
> 
> Reported-by: Aili Yao <yaoaili@...gsoft.com>
> Cc: Aili Yao <yaoaili@...gsoft.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>