Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 5

[Shannon Zhao <zhaoshenglong@xxxxxxxxxx>]

On 2015/8/31 19:44, Julien Grall wrote:
> 
> 
> On 29/08/2015 02:00, Shannon Zhao wrote:
>> Hi Julien,
>>
>> On 2015/8/28 20:55, Julien Grall wrote:
>>> Hi Shannon,
>>>
>>> On 28/08/15 10:45, Shannon Zhao wrote:
>>>> 2. Copy and change some EFI and ACPI tables
>>>> -------------------------------------------
>>>
>>> [..]
>>>
>>>> All above tables will be mapped to Dom0 non-RAM space(e.g. the space
>>>> after Dom0 RAM).
>>>
>>> If I understand correctly what you are saying, you plan to put the
>>> tables just after the Dom0 RAM bank. Although, there can be multiple
>>> banks and how can you be so sure that there will be no MMIO at this
>>> place?
>>>
>>>
>>
>> Currently I use the last RAM bank(kinfo->mem.bank[nr_banks - 1]) to
>> calculate the start address of non-RAM place. I'm not sure there will be
>> no MMIO at that place. Do you have any good idea to find such sure and
>> safe non-ram place?
> 
> It's not a safe place because with the direct mapping for the RAM, DOM0
> RAM could live in the last bank. 

I put the tables after the last bank currently.

> Furthermore, for the grant table
> region, we are re-using the RAM region used by Xen (find_gnttab_region),
> so it may clash with it too because Xen is relocated as high as possible.
> 

Oh, I didn't realize this.

> Although, given that the grant table region will be found by Linux when
> ACPI is used (see your section 3.), we could be able to re-use the Xen
> region to store the new tables/structures.
> 

So you mean it's fine to put the tables after last bank of Dom0 RAM?

In addition, how does UEFI find the space to place the tables? Could we
use the same way?

Thanks,
-- 
Shannon


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