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

[Shannon Zhao <shannon.zhao@xxxxxxxxxx>]

On 2015/8/27 22:13, Jan Beulich wrote:
> > > > On 27.08.15 at 15:50, <shannon.zhao@xxxxxxxxxx> 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

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