Re: Design doc of adding ACPI support for arm64 on Xen - version 4

[Shannon Zhao <shannon.zhao@linaro.org>]

On 2015/8/27 22:13, Jan Beulich wrote:
>>>> On 27.08.15 at 15:50, <shannon.zhao@linaro.org> wrote:
>> On 2015/8/27 15:52, Jan Beulich wrote:
>>> One other aspect completely left off so far is that of proper isolation:
>>> What x86 exposes to Dom0 is specifically limited to what Dom0 is
>>> supposed to know. I'm getting the impression that by exposing more
>>> EFI tables this is being violated just for the purpose of avoiding any
>>> changes to Linux. But maybe I'm misremembering, and all the extra
>>> tables exposed are actually fake ones rather than cloned host ones.
>>
>> Currently we create EFI system table and EFI memory descriptor table as
>> Linux requires. I think the EFI memory descriptor table is necessary.
>> What we didn't reach an agreement is only the EFI system table. Yes, we
>> only use the Configure table of the EFI system table to get the ACPI
>> root address. As you mentioned before, it could pass only the Configure
>> table to Dom0, but we should change the process of parsing the DT and
>> consider the backwards compatibility.
>
> A made up system table would (as said before) be fine with me too.
> Just not a clone of the host one.
>

Yeah, it's a made up one.

>> On the other hand, as the RUNTIME service is not supported, it could
>> assign the runtime service members of EFI system table invalid values
>> and let Dom0 not initialize RUNTIME service(This could be done by making
>> the memory attribute not be EFI_MEMORY_RUNTIME when we create the EFI
>> memory descriptor table). If the RUNTIME service is supported in the
>> future, it doesn't need to change the Linux again. So it could avoid
>> changing back.
>
> I'd strongly advise against such hackery - it will get you (and Xen)
> into the bad firmware corner. EFI without runtime services doesn't
> exist. And runtime services code/data not marked as such are a
> firmware bug (sadly existing in reality on the x86 side). But remember
> that under Xen the Dom0 kernel mustn't care about runtime services
> (other than wanting to be able to invoke them through hypercalls).
>

Oh, I see. Thanks for your explanation.

-- 
Shannon