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SubjectRe: PCI memory allocation bug with CONFIG_HIGHMEM

On Wed, 7 Jan 2004, Eric W. Biederman wrote:
>
> However insert_resource does not quite match what I think needs to
> happen. After a pci quirk applies insert_resource I will get
> something like:
>
> fff0000-ffffffff : BIOS ROM Window
> ffff0000-ffffffff : reserved
>
> With the reserved region still present and marked as BUSY.

I would suggest ignoring it. Not only because being overly complicated is
bad, but simply because nobody should care.

At some point adding extra regions is _purely_ for "documentation"
reasons, and while that may be nice, it's not worth worrying about. The
only thing you really want from a _correctness_ standpoint is to make sure
that nobody else will try to allocate their stuff in that area, and your
"BIOS ROM Window" resource should do that already.
> Would it be reasonable to write a variant of request_resource that just
> drops BIOS resources.

It would not be impossible to just have a "force_resource()" that would
simply override _any_ existing resource, but quite frankly, I'd be more
nervous about that.

We could also mark the e820 non-RAM resources with some special
IORESOURCE_TENTATIVE flag, and allow just overriding those.

But even the simple "insert_resource()" has some potential problems: if
the BIOS has allocated the minimal window for itself (64kB at 0xffff0000),
and has allocated some _other_ chip at 0xfffe0000 that the kernel doesn't
know about yet, your insert_resource() would do the wrong thing and claim
the whole area for the BIOS writing.
Maybe that doesn't happen, but it's something to think about.

At some point, the _correct_ answer may be: don't do complex things, and
write a bootable floppy (without any OS at all, or a really minimal one)
to do BIOS rom updates.

Linus
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