Re: [Xen-devel] loading custom ACPI tables?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.04.13 at 12:48, Eric Shelton <eshelton@xxxxxxxxx> wrote:
> Unfortunately, I managed to hit the few portions looked at by the
> hypervisor, as I am modifying the IOAPIC information in MADT and IVRS
> (as well as PCI slot interrupt info in DSDT, although that does not
> appear to be looked at by the hypervisor).

So I guess you're trying to work around the fallout of XSA-36?

> A question on how Xen gathers platform info: Xen appears to use the MP
> tables as a starting point for determining the number of IOAPICs.  Is
> the hypervisor code capable of not using the MP tables, and solely
> collecting this information from ACPI?  It would be nice not to

No, the MP tables should get looked at consulted only when there's
no respective ACPI data.

> In terms of implementing passing in custom ACPI tables, I was
> considering adding an additional "module" line in the grub
> configuration (assuming a third one is permitted) to essentially a
> copy of the in-memory structure, and looking for a magic number (which
> will likely already be part of the ACPI tables).  I am aware of, but I
> have not reviewed, the Linux initrd-based override code.  However, I'm
> not sure whether the Xen development philosophy would prefer (1) code
> reuse (if reasonably portable), even if it involves adding something
> with the complexity of digging through an initrd; or (2) something
> simpler with fewer LOC.  Other suggestions are welcome.

More than two modules is possible, and in fact already being used
(for XSM an microcode loading), so you'd need to look at the code
that's already there to make sure your ACPI table pseudo module(s)
won't get mistreated.

You certainly should not look at the initrd - format and contents
are defined/used by the kernel, hence no assumptions should be
made.

Jan


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