Re: The vcpu won't be wakened for a long time

From: Sean Christopherson <seanjc@google.com>
To: "Longpeng (Mike,
	Cloud Infrastructure Service Product Dept.)" 
	<longpeng2@huawei.com>
Cc: "pbonzini@redhat.com" <pbonzini@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Gonglei (Arei)" <arei.gonglei@huawei.com>,
	Huangzhichao <huangzhichao@huawei.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: The vcpu won't be wakened for a long time
Date: Tue, 14 Dec 2021 17:36:21 +0000	[thread overview]
Message-ID: <YbjWFTtNo9Ap7kDp@google.com> (raw)
In-Reply-To: <73d46f3cc46a499c8e39fdf704b2deaf@huawei.com>

On Tue, Dec 14, 2021, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
> Hi guys,
> 
> We find a problem in kvm_vcpu_block().
> 
> The testcase is:
>  - VM configured with 1 vcpu and 1 VF (using vfio-pci passthrough)
>  - the vfio interrupt and the vcpu are bound to the same pcpu
>  - using remapped mode IRTE, NOT posted mode

What exactly is configured to force remapped mode?

> The bug was triggered when the vcpu executed HLT instruction:
> 
> kvm_vcpu_block:
>     prepare_to_rcuwait(&vcpu->wait);
>     for (;;) {
>         set_current_state(TASK_INTERRUPTIBLE);
> 
>         if (kvm_vcpu_check_block(vcpu) < 0)
>             break;
> 					<------------ (*)
>         waited = true;
>         schedule();
>     }
>     finish_rcuwait(&vcpu->wait);
> 
> The vcpu will go to sleep even if an interrupt from the VF is fired at (*) and
> the PIR and ON bit will be set ( in vmx_deliver_posted_interrupt ), so the vcpu
> won't be wakened by subsequent interrupts.
> 
> Any suggestions ? Thanks.

What kernel version?  There have been a variety of fixes/changes in the area in
recent kernels.