Re: PCI memory allocation bug with CONFIG_HIGHMEM

[Linus Torvalds]

On Tue, 6 Jan 2004, Adam Belay wrote:
>
> 5.) Look into other ways of finding out if the PnPBIOS might be buggy,
> currently we only have DMI.
> 
> Any others?

We could use the exception mechanism, and try to fix up any BIOS errors. 
That would require:

 - make the BIOS calls save all important registers just before entry (esp 
   in particular, and the "after-call EIP") and set a flag saying "fix me 
   up". Do this per-CPU. Clear the flags after exit.

 - add magic knowledge to "fixup_exception()" path that looks at the 
   per-cpu fix-me-up flag, and if it is set, restore all the segments 
   (which the BIOS may have crapped on), %esp and %eip to the magic fixup 
   values.

 - test it with a bogus trap (on purpose) which has reset all the x86 
   registers, including an offset %esp.

This could make us recover from some (most?) BIOS bugs and at least 
dynamically notice when the BIOS does bad bad things.

		Linus
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