Re: [Xen-devel] [PATCH v2 6/6] xen/arm: grant table

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 23 Jul 2012, Ian Campbell wrote:
> On Fri, 2012-07-20 at 16:05 +0100, Stefano Stabellini wrote:
> > Implement XENMAPSPACE_grant_table and grant_table_op.
> > 
> > Introduce an HVM_PARAM to tell the guest where to map the grant table
> > (HVM_PARAM_GRANT_START_PFN), similarly to what we do with
> > HVM_PARAM_CONSOLE_PFN and HVM_PARAM_STORE_PFN.
> > However HVM_PARAM_GRANT_START_PFN is also going to be used by dom0, so
> > we set the parameter in Xen rather than libxc.
> > Using HVM_PARAM_GRANT_START_PFN removes the need for a platform pci
> > device.
> 
> In principal the guest can use whatever free (or not free) PFN space it
> wants for this region, right?
> 
> I suspect hybrid on x86 has a similar requirement and if we are going to
> add this sort of thing we should make sure that we can satisfy both
> architectures.
> 
> Or would it be better to use existing per-arch mechanisms to describe
> the memory map (E820 on x86 and DTB on ARM)? They already describe the
> rest of the memory layout.
> 
> The foreign page mapping stuff also needs to find a similar PFN region
> to use.

I think that you are right.
In fact I have a prototype implementation using a memory range specified
under a "/xen" node in the DT.

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