Re: [Xen-devel] [PATCH for-4.10] libxc: load acpi RSDP table at correct address

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/20/2017 09:14 AM, Juergen Gross wrote:
> On 20/11/17 14:56, Boris Ostrovsky wrote:
>> On 11/20/2017 06:50 AM, Jan Beulich wrote:
>>>>>> On 20.11.17 at 12:20, <jgross@xxxxxxxx> wrote:
>>>> Which restriction? I'm loading the RSDP table to its architectural
>>>> correct addres if possible, otherwise it will be loaded to the same
>>>> address as without my patch. So I'm not adding a restriction, but
>>>> removing one.
>>> What is "architecturally correct" in PVH can't be read out of
>>> specs other than what we write down. When there's no BIOS,
>>> placing anything right below the 1Mb boundary is at least
>>> bogus.
>> Unless it's a UEFI boot -- where else would you put it? Aren't these two
>> (UEFI and non-UEFI) the only two options that the ACPI spec provides?
> I think Jan is right: for PVH its _our_ job to define the correct
> placement. 

Yes, and if it is placed in a non-standard location then the guest will
have to deal with it in a non-standard way. Which we can in Linux by
setting acpi_rsdp pointer in the special PVH entry point, before jumping
to Linux "standard" entry --- startup_{32|64}().

But if your goal is to avoid that special entry point (and thus not set
acpi_rsdp) then how do you expect kernel to find RSDP?

> Which still can be the same as in the BIOS case, making
> it easier to adapt any guest systems.
>
> So I'd say: The RSDP address in PVH case is passed in the PVH start
> info block to the guest. In case there is no conflict with the
> physical load address of the guest kernel the preferred address of
> the RSDP is right below the 1MB boundary.

And what do we do if there *is* a conflict?


-boris


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