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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.08.15 at 02:37, <julien.grall@xxxxxxxxxx> wrote:
> On 20/08/2015 19:25, Shannon Zhao wrote:
>> On 2015/8/20 22:06, Jan Beulich wrote:
>>> So can the two of you please sort out whether these are Linux
>>> internal tags (which Xen has no business generating, or even
>>> knowing of) or some form of publicly documented interface?
>>
>> They are Linux internal tags. But to support Xen ACPI on ARM, we just
>> reuse the existing mechanism to pass the information to Dom0.
> 
> My previous mail was unclear, sorry. I was explaining the current usage 
> of those properties because you seemed to be concern about the backward 
> compatibility.
> 
> We'd like to formalize those properties in order to use them to pass 
> information between Xen and the kernel image.

Ah, that clarifies things. Thanks.

> This would avoid us to create a Xen specific entry path in the kernel 
> and use the non-EFI one (also used by the EFI stub) and make easier to 
> support new DOM0 OS (for instance FreeBSD).
> 
> So I totally agree with Shannon mails.

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.

Jan


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