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
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