Re: [Xen-devel] [Draft F] Xen on ARM vITS Handling

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-06-12 at 10:05 -0400, Julien Grall wrote:
> 
> On 12/06/2015 09:32, Julien Grall wrote:
> >
> >
> > On 12/06/2015 09:16, Ian Campbell wrote:
> >> On Fri, 2015-06-12 at 09:09 -0400, Julien Grall wrote:
> >>> Hi Ian,
> >>>
> >>> On 12/06/2015 04:52, Ian Campbell wrote:
> >>>> On Fri, 2015-06-12 at 14:07 +0530, Vijay Kilari wrote:
> >>>> So pLPIs must be routed at device assignment time because in the vLPI
> >>>> configuration table trap there is no mapping back to a single pLPI.
> >>>
> >>> I just remembered the exact reason that made use to differ SPI enabling.
> >>
> >> I can't parse this sentence, differ how?
> >
> > deferring sorry.
> >
> >>
> >>> When the device is assigned, the domain VCPUs are still down (even
> >>> VCPU0).
> >>>
> >>> If we receive an interrupt before the VCPU0 is unpaused, the interrupt
> >>> will be lost. Same if the interrupt is not yet configured (i.e before
> >>> the vITS setup correctly the table) with your proposal.
> >>
> >> Is this any different to booting with the ITT not setup?
> >
> > I don't understand your question.
> >
> >> (SPIs are a slightly different case because they don't need h/w routing)
> >
> > I think you mixed PPIs with SPIs. SPIs (shared private interrupt)
> 
> s/private/processor/

It's "peripheral" ;-)

> 
> > requires h/w routing.
> >
> >>
> >>> This could happen when the device is not quiescent. We had this issue on
> >>> the vexpress at boot time when the network card was trying to send an
> >>> interrupt before DOM0 is setup.
> >>
> >> I don't fully understand the issue you are trying to describe, but do
> >> you want to propose a change to the spec?
> >
> > I actually don't know how to modify it. So it's an open question.
> >
> > vgic_vcpu_inject_irq doesn't queue the interrupt if a VCPU is down. I
> > think this is because the state of the VCPU wouldn't be correct.
> >
> > The process would be something like:
> >
> >      - Creation of the domain
> >      => All vCPUs are down
> >
> >      - Device is assigned to the guest
> >          => Enable physical LPIs
> >
> >      * physical LPI is received *
> >      => Will be ignored and not EOIed (VCPU0 is down)
> >          => The LPI will never fired again during the guest life
> >
> >      -  Domain is started by the toolstack
> >           => VCPU0 is online
> >
> > Regards,
> >
> 



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