Re: [Xen-devel] [PATCH V6 01/10] xen/arm: gic-v3: Increase the size of GICR in address space for guest

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-06-05 at 17:04 +0100, Julien Grall wrote:
> On 05/06/15 16:49, Ian Campbell wrote:
> > On Mon, 2015-06-01 at 20:56 +0800, Chen Baozi wrote:
> >> From: Chen Baozi <baozich@xxxxxxxxx>
> >>
> >> Currently it only supports up to 8 vCPUs. Increase the region to hold
> >> up to 128 vCPUs, which is the maximum number that GIC-500 supports.
> >>
> >> Signed-off-by: Chen Baozi <baozich@xxxxxxxxx>
> >> Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > 
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > 
> > I did briefly wonder if we should shoot for the stars here and reserve
> > space for some enormous set of processors, but I suppose there's no
> > need.
> 
> I though about the same things. AFF0 + AFF1 gives 4096 CPUs.
> 
> Although as we will support only 128 vCPUs (see the last patch),
> reserving more space is not necessary. This space saved can be used for
> a bigger PCI MMIO region later.

I don't think rdistr regions need to be contiguous, so we could consider
(not now, when it happens) putting CPUs 128+ into the gap above 4G, on
the basis that a guest with that many CPUs is almost certainly going to
have tonnes of RAM and therefore be 64 bit...

Ian.


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