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

[Julien Grall <julien.grall@citrix.com>]

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. 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.

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.

Regards,
-- 
Julien Grall