Re: [PATCH for-4.15] xen/vgic: Implement write to ISPENDR in vGICv{2, 3}

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 23/02/2021 01:24, Stefano Stabellini wrote:
> On Mon, 22 Feb 2021, Bertrand Marquis wrote:
> > > On 20 Feb 2021, at 14:04, Julien Grall <julien@xxxxxxx> wrote:
> The consequence of this patch is that a guest can cause vcpu_unblock(v),
> hence vcpu_wake(v), to be called for its own vcpu, which basically
> always changes v to RUNSTATE_runnable. However, that alone shouldn't
> allow v to always come up ahead of any other vcpus in the queue, right?
> It should be safe. I just wanted a second opinion on this :-)
vcpu_wake() only tells the scheduler that the vCPU can be run, it is 
then up to the scheduler to decide what to do. AFAIU, for credit{1, 2}, 
each vCPU will have some credit. If you run out of credit, then you vCPU 
will not be descheduled if there is work do it.
> It was possible to trigger interrupts for your own vcpus even before, but
> now the code path is going to be direct for virtual interrupts.
You can already trigger "directly" virtual interrupts using the event 
channels.
Cheers,

--
Julien Grall