Re: [Xen-devel] [PATCH V6 05/10] xen/arm64: gicv3: Use AFF1 when translating ICC_SGI1R_EL1 to cpumask

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-06-05 at 19:25 +0100, Julien Grall wrote:
> 
> On 05/06/2015 17:09, Ian Campbell wrote:
> >> +         * injection, ignoring level 2 & 3.
> >> +         */
> >> +        if ( gicv3_sgir_to_cpumask(&vcpu_mask, sgir) )
> >> +        {
> >> +            gprintk(XENLOG_WARNING, "Wrong affinity in SGI1R_EL 
> >> register\n");
> >
> > I don't think we need to log this. The guest has asked to send an SGI to
> > a VCPU which we know can't possibly exist. I'm not sure what real h/w
> > would do, but if it is e.g. UNPREDICTABLE then we should consider
> > killing the guest here. I suspect it's actually just ignored, in which
> > case we can silently do the same.
> 
>  From the spec:
> 
> "Note: if a bit is one and the bit does not correspond to a valid target 
> processor, the bit must be ignored by the Distributor. In such cases, a 
> Distributor may optionally generate an SEI."
> 
> The implementation of SEI is implementation defined. I'm not sure what 
> would be the right behavior to adopt here.

In general I'm in favour of being as harsh as allowed by default (i.e.
without a good reason to do otherwise), to avoid guests coming to rely
on lenient behaviour which we might find we want to change in the
future.

Ian


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