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



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)

-boris

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