Re: [PATCH 2/4] KVM: VMX: avoid double list add with VT-d posted interrupts

From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Longpeng <longpeng2@huawei.com>,
	Huangweidong <weidong.huang@huawei.com>,
	Gonglei <arei.gonglei@huawei.com>,
	wangxin <wangxinxin.wang@huawei.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH 2/4] KVM: VMX: avoid double list add with VT-d posted interrupts
Date: Fri, 9 Jun 2017 09:29:45 +0200	[thread overview]
Message-ID: <821f022f-ff94-876d-2426-8b6ab35af65f@redhat.com> (raw)
In-Reply-To: <20170609025044.GH3628@pxdev.xzpeter.org>

On 09/06/2017 04:50, Peter Xu wrote:
> Even, I'm thinking whether we can unconditionally setup PDST only in
> pi_load(), then post_block() only needs to handle the NV bit.

No, you can't do that without fiddling with the blocked_vcpu lists in
pi_load.

> (PS. since I'm at here... could I ask why in pi_pre_block we need to
>  udpate PDST as well? I guess that decides who will run the
>  wakeup_handler code to kick the vcpu thread, but would that really
>  matter?)

For this one it's a yes. :)  I think it's not needed anymore indeed
after these patches; see this comment:

                /*
                 * The wakeup_handler expects the VCPU to be on the
                 * blocked_vcpu_list that matches ndst.  Interrupts
                 * are disabled so no preemption should happen, but
                 * err on the side of safety.
                 */

So we could add a WARN.

Paolo