Re: [Xen-devel] question about memory allocation for driver domain

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-02-09 at 19:16 +0800, Julien Grall wrote:
> >> The last problem but not the least is, depending on which backend you
> >> are running in the 1:1 domain (such blkback), grant won't be mapped 1:1
> >> to the guest, so you will have to use swiotlb in order to use the right
> >> DMA address. For instance, without swiotlb, guest won't be able to use a
> >> disk partition via blkfront. This because the backend is giving directly
> >> the grant address to the block driver. To solve this, we have to use
> >> swiotlb and set specific DMA callback. For now, there are only used for
> >> DOM0.
> >
> > Not much we can do here except extend the dom0 code here to
> > conditionally enable itself for other domains.
> 
> You mean in the guest kernel? Maybe we have to introduce a new feature 
> flags indicating is the domain is using 1:1 mapping or not?

Something along those lines I would expect.

I'm not sure it fits, but this has some similarities with the DTB
bindings used to indicate to the guest that a device is protected (in
the SMMU sense) which you did a while back. It's possible we could reuse
or extend that interface -- after all 1:1 is somewhat like having an
SMMU, at least to the extent that the things the guest is expected to do
are the same.

Ian.


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