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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 21/11/17 07:44, Jan Beulich wrote:
>>>> On 20.11.17 at 17:59, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 11/20/2017 11:43 AM, Jan Beulich wrote:
>>>>>> On 20.11.17 at 17:28, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>> On 11/20/2017 11:26 AM, Jan Beulich wrote:
>>>>>>>> On 20.11.17 at 17:14, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>>>> What could cause grub2 to fail to find space for the pointer in the
>>>>>> first page? Will we ever have anything in EBDA (which is one of the
>>>>>> possible RSDP locations)?
>>>>> Well, the EBDA (see the B in its name) is again something that's
>>>>> meaningless without there being a BIOS.
>>>> Exactly. So it should always be available for grub to copy the pointer
>>>> there.
>>> But what use would it be if grub copied it there? It just shouldn't
>>> be there, neither before nor after grub (just like grub doesn't
>>> introduce firmware into the system).
>> So that the guest can find it using standard methods. If Xen can't
>> guarantee ACPI-compliant placement of the pointer then someone has to
>> help the guest find it in the expected place. We can do it with a
>> dedicated entry point by setting the pointer explicitly (although
>> admittedly this is not done correctly now) or we need to have firmware
>> (grub2) place it in the "right" location.
>>
>> (It does look a bit hacky though)
> Indeed. Of course ACPI without any actual firmware is sort of odd,
> too. As to dedicated entry point and its alternatives: Xen itself
> tells grub (aiui we're talking about a flavor of it running PVH itself)
> where the RSDP is. Why can't grub forward that information in a
> suitable way (e.g. via a new tag, or - for Linux - as a new entry
> in the Linux boot header)?

Or if the worst comes to the worst, fabricate an acpi_rsdp= command line
parameter?

~Andrew

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