Re: [PATCH v2] kvm: Replace vcpu->swait with rcuwait

[Paolo Bonzini <pbonzini@redhat.com>]

On 20/04/20 23:50, Davidlohr Bueso wrote:
> On Mon, 20 Apr 2020, Paolo Bonzini wrote:
> 
>> On 20/04/20 22:56, Davidlohr Bueso wrote:
>>> On Mon, 20 Apr 2020, Marc Zyngier wrote:
>>>
>>>> This looks like a change in the semantics of the tracepoint. Before
>>>> this
>>>> change, 'waited' would have been true if the vcpu waited at all. Here,
>>>> you'd
>>>> have false if it has been interrupted by a signal, even if the vcpu
>>>> has waited
>>>> for a period of time.
>>>
>>> Hmm but sleeps are now uninterruptible as we're using TASK_IDLE.
>>
>> Hold on, does that mean that you can't anymore send a signal in order to
>> kick a thread out of KVM_RUN?  Or am I just misunderstanding?
> 
> Considering that the return value of the interruptible wait is not
> checked, I would not think this breaks KVM_RUN.

What return value?  kvm_vcpu_check_block checks signal_pending, so you
could have a case where the signal is injected but you're not woken up.

Admittedly I am not familiar with how TASK_* work under the hood, but it
does seem to be like that.

Paolo