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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 08/06/2014 05:45 PM, Stefano Stabellini wrote:
> 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.

Last time you told me about graphics card. But we don't have any board
with graphic card and IOMMU supported by Xen.
In any case the developer will have to modify Xen to add the new
platform. It won't hurt to add a new region at this time.

Regards,

-- 
Julien Grall

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