Xen devel - Jul 2005 - DMI and other BIOS hooks

Hi Folks,
Can someone please offer an explanation or pointer to docs for how Xen
maps BIOS facilities into guest space?  Specifically, I have a DMI BIOS
problem that is causing Xen to call domain_crash() on Dom0 during
boot-up.

Here''s a few specific questions:
1) Does Xen map the platform''s 0xF0000-0xFFFFF BIOS space to guests, or
is this region virtualized?
2) If virtualized, how Xen map BIOS facilities to guests?

In my case, Dom0 finds the _DMI_ entry point, which appears to overlap
with physical RAM.  This ultimately causes the domain_crash() for Dom0.
Looks like a bad BIOS, but I''m unclear as to the degree which Xen plays
man-in-the-middle.

Any thoughts are most appreciated.

Thanks for your time,
-steve




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On 26 Jul 2005, at 19:11, King, Steven R wrote:
> Here''s a few specific questions:
> 1) Does Xen map the platform''s 0xF0000-0xFFFFF BIOS space to
guests, or
> is this region virtualized?
> 2) If virtualized, how Xen map BIOS facilities to guests?
>
> In my case, Dom0 finds the _DMI_ entry point, which appears to overlap
> with physical RAM.  This ultimately causes the domain_crash() for Dom0.
> Looks like a bad BIOS, but I''m unclear as to the degree which Xen
plays
> man-in-the-middle.
Memory space that is reserved by the e820 table is marked as ''I/O 
memory'' by Xen. Domain0 is allowed to map such areas as it wishes. If 
you have a broken BIOS that is not reserving the table areas in its 
e820, Xen will not mark the area as I/O memory and will prevent domain0 
from mapping that memory. Hence the crash.

We may need a workaround for broken BIOSes (perhaps even if it''s just a
boot parameter to Xen to specify reserved memory ranges).

  -- Keir


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