Re: [Xen-devel] [RFC PATCH 21/24] ARM: vITS: handle INVALL command

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 03/12/16 00:46, Stefano Stabellini wrote:
> On Fri, 2 Dec 2016, Andre Przywara wrote:
> > > When we receive the maintenance interrupt and we clear the LR of the
> > > vLPI, Xen should re-enable the pLPI.
> > > Given that the state of the LRs is sync'ed before calling gic_interrupt,
> > > we can be sure to know exactly in what state the vLPI is at any given
> > > time. But for this to work correctly, it is important to configure the
> > > pLPI to be delivered to the same pCPU running the vCPU which handles
> > > the vLPI (as it is already the case today for SPIs).
> > Why would that be necessary?
> Because the state of the LRs of other pCPUs won't be up to date: we
> wouldn't know for sure whether the guest EOI'ed the vLPI or not.
Well, there is still a small window when the interrupt may be received 
on the previous pCPU. So we have to take into account this case.
This window may be bigger with LPIs, because a single vCPU may have 
thousand interrupts routed. This would take a long time to move all of 
them when the vCPU is migrating. So we may want to take a lazy approach 
and moving them when they are received on the "wrong" pCPU.
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel