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

[Sean Christopherson <seanjc@google.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.