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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Shannon,
On 01/09/15 05:12, Shannon Zhao wrote:
> I tried this. Directly use the "kinfo->gnttab_start = __pa(_stext)" as
> the address where these tables are mapped to Dom0. But the value of
> gnttab_start is lower than the start of RAM, so Dom0 ingore these
> regions and boot failed. see early_init_dt_add_memory_arch()

Can you elaborate? How Linux will fail? If this region is marked as
reserved in the UEFI memory map, Linux will mark the memory as reserved.

Furthermore, *ioremap is used in order to map the EFI tables so I don't
see a reason to fail.

>>>
>>> In addition, how does UEFI find the space to place the tables? Could we
>>> use the same way?
>>
>> I think that those tables are living in the RAM and region used are
>> marked as reserved.
>>
> 
> So can we use the same way for Dom0? I think the Linux will reserve the
> regions for EFI in reserve_regions(). Therefore, Dom0 will not use these
> reserved regions for other use.

Jan had some concerned about putting the EFI tables in RAM owned by DOM0
(see [1]).

Can you explain how Linux behave with EFI tables. I.e:
        - Where tables are expected to live (RAM, others...)?
        - Are thoses regions freed at some point to be re-use?
        - ...

Regards,

[1] http://lists.xen.org/archives/html/xen-devel/2015-08/msg02167.html

-- 
Julien Grall

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