Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

[Tim Deegan <tim@xxxxxxx>]

At 14:38 +0000 on 08 Dec (1512743913), Julien Grall wrote:
> On 08/12/17 08:03, Tim Deegan wrote:
> > +1 for avoiding the full majesty of PoD if you don't need it.
> > 
> > It should be possible to do something like the misconfigured-entry bit
> > trick by _allocating_ the memory up-front and building the p2m entries
> > but only making them usable by the {IO}MMUs on first access.  That
> > would make these early p2m walks shorter (because they can skip whole
> > subtrees that aren't marked present yet) without making major changes
> > to domain build or introducing run-time failures.
> 
> I am not aware of any way on Arm to misconfigure an entry. We do have 
> valid and access bits, although they will affect the IOMMU as well. So 
> it will not be possible to get page-table sharing with this "feature" 
> enabled.

How unfortunate.  How does KVM's demand-population scheme handle the IOMMU? 

Tim.

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