Re: [Xen-devel] [PATCH v2 2/5] arm: implement vcpu_mark_events_pending

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-02-24 at 14:15 +0000, Stefano Stabellini wrote:
> On Fri, 24 Feb 2012, David Vrabel wrote:
> > On 24/02/12 10:33, Ian Campbell wrote:
> > > On Thu, 2012-02-23 at 18:21 +0000, Stefano Stabellini wrote:
> > >> Implement vcpu_mark_events_pending using the vgic to inject INT 63, that
> > >> we reserve for Xen usage.
> > > 
> > > Does this require a trap when the guest acks or EOIs this interrupt?
> > > What about maintenance interrupts arising from injecting this?
> 
> Yes, we would get a maintenance interrupt in the hypervisor every time
> the guest EOI's it.

We really want to avoid those.

> > > Might we want to instead inject this interrupt as an SGI, so that it
> > > appears as a per-VCPU interrupt?
> > 
> > I don't think it's possible to register a SGI handler in Linux
> > currently.  The mapping of IRQ numbers to GIC interrupts skips over the
> > SGIs.  This would be easy to fix I think.
> 
> A per-vcpu interrupt that doesn't require an EOI would be ideal, however
> like David wrote, it is not possible to register an SGI handler in Linux
> at the moment. I'll give it a look though.

Do SGIs avoid the EOI and maintenance interrupt issues though?

Ian.



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