Re: [Xen-devel] [PATCH v2 19/21] xen/arm: Reserve region in guest memory for device passthrough

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 6 Aug 2014, Stefano Stabellini wrote:
> On Wed, 6 Aug 2014, Julien Grall wrote:
> > Hi Stefano,
> > 
> > On 08/06/2014 05:27 PM, Stefano Stabellini wrote:
> > > On Thu, 31 Jul 2014, Julien Grall wrote:
> > >> This region will be split by the toolstack to allocate MMIO range for eac
> > >> device.
> > >>
> > >> For now only reserve a 768MB region, this should be enought to 
> > >> passthrough
> > >> multiple device at the same time.
> > >>
> > >> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > >>
> > >> ---
> > >>
> > >> I can't allocate easily a range of 1GB in the current layout without 
> > >> shrink
> > >> the first RAM bank. So I decided to use only 768MB. If in the future we 
> > >> need
> > >> more, then we will have to choose at runtime the guest layout.
> > >>
> > >>     Changes in v2:
> > >>         - Bump the reserved region from 512MB to 768MB
> > > 
> > > 
> > > Better than nothing.
> > > Would it be possible to add a second region > 4GB? Maybe after RAM?
> > > How hard would be to handle that?
> > 
> > It won't work if the guest is using short-descriptor translation table
> > format because only 32 bits address will be supported.
> 
> I know.

However it would make things easier if you want to assign a device with
a large MMIO region to a guest that can handle it.

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