Re: [Xen-devel] [RFC 0/2] Cap SMMU s2 input-size based on p2m tables

["Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>]

On Tue, Apr 28, 2015 at 05:50:43PM +0100, Julien Grall wrote:
> On 27/04/15 10:24, Edgar E. Iglesias wrote:
> > From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxxx>
> > 
> > Hi,
> 
> Hi Edgar,
> 
> > This is a first try at fixing the issue I'm seeing on ZynqMP with
> > missmatched setup of the SMMU and the shared page-tables with p2m.
> > 
> > I've only handled the case of having an SMMU that supports larger
> > s2 input-sizes than what p2m wants to use.
> > 
> > To support the case were the system has SMMUs that can only do smaller
> > input-sizes than the CPU, I think we will need to walk the device-tree
> > when creating domains and somehow cap the p2m IPA size to the largest
> > supported S2 size across the SMMUs used by that particular domain.
> > The max IPA size may need to be domain specific.
> > I did not implement this but I did make the max size domain specific.
> > Julien, you mentioned you might have access to such a system?
> 
> Right, I got an AMD Seattle where the IPA is limited by the SMMU. From
> Xen output:
>    - SMMU: 40-bit IPA -> 40-bit PA
>    - P2M: 44-bit IPA with 44-bit PA
> 
> Suravee, can you confirm that this is actually the case?
> 
> > 
> > Does this look reasonable or should we be fixing this some other way?
> > I could make the patch simpler I guess by having a global (not
> > domain specific) max value set once aswell.
> 
> For your use case a global seems better (you may need to move the
> iommu_setup call after setup_virt_paging).

OK, I'll implement that and we can incrementally add a per-domain
values if needed.

> Although, if the limitation of the SMMU on Seattle is confirmed, that
> would restrict domain memory to 1TB maximum (rather than 16TB) on this
> platform.

Right, with the domain specific max ipa value, we could limit the address
space only for guests that actually use the SMMU. Not sure how much value
there is in that though...

Thanks!

Cheers,
Edgar


> 
> Regards,
> 
> -- 
> Julien Grall

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