Re: [PATCH RFC] function probe_roms accessing improper addresses

From: Randy Wright
Date: Tue Oct 23 2012 - 12:04:58 EST

Hi Matthew,

You made some interesting suggestions:

> 1) Declare that any x86 hardware supported by Linux *must* support
> probing in this address region

On the first: one way to be compliant with such a requirement would be
to design systems that implement softfail in this particular region.
What about a system that hardfails, but on which the resulting machine
check can be handled by the kernel machine check handler? Would
appropriate re-ordering of the kernel initialization code to support
such systems be acceptable?

Also, let me mention a possible amendment to your first idea: what if
the mandate that probing be supported were qualified by some attribute
that could be indicated in the UEFI environment? For example: instead
of just a hole in the UEFI memory map, what if this range was
specifically present and typed as EfiUnusableMemory? Another idea for
UEFI systems - but one requiring a UEFI specification change - might be
adding a UEFI variable that if present, indicates any area not
explicitly included and typed in the UEFI memory map (including the
legacy adapter region) must be explicitly avoided by an OS.

> 2) Don't call probe_roms() by default, but leave it up to the graphics
> drivers. If they can get the rom by any other means then don't call it.

One the second idea: there are a quite a lot of video drivers in the kernel
source tree. Do you have a suggestion for how to evaluate which ones
rely on the setup performed by probe_roms?

Randy Wright Hewlett-Packard Company
Phone: (970) 898-0998 Mail: rwright@xxxxxx
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