Re: [Xen-devel] [PATCH v3 10/24] xen/arm: gic: Add sanity checks gic_route_irq_to_guest

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-02-20 at 17:28 +0000, Julien Grall wrote:
> Hi Ian,
> 
> On 20/02/15 16:07, Ian Campbell wrote:
> > More importantly: We have (hopefully) guaranteed elsewhere that an PPI
> > or SGI can never make it here, I take it. If that's the case then either
> > the comment should say that, or more likely, the comment is redundently
> > restating the assert's condition.
> 
> I will update the comment to /* Caller has already checked that the IRQ
> is an SPIs */

Just "SPI", but otherwise sounds good.

> > Care needs to be taken here that priority is not under unfettered guest
> > control -- since this configures the physical GIC we need to e.g. ensure
> > that Xen's own IPIs have higher priority than anything a guest can ever
> > set. (Realistically this probably means we want to constrain guests to
> > the bottom half of the priority range and expose different BPR etc in
> > the vgic, out of scope here though)
> 
> The priority is controlled by route_irq_to_guest and set statically
> using GIC_PRI_IRQ.
> 
> If we decide to hardcoded the priority here, we should drop the
> parameter on gic_route_irq_guest. But not keeping both.

There is a middle ground, which is for guest-routed IRQs to be allowed a
subset of the real priorities, but until those associated checks are in
place I think hardcoding in gic_route_irq_to_guest leaves less scope for
mistakes.

Ian.


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