linux-kernel - Re: [PATCH 5/5] PNP: HP nx6325 fixup: reserve unreported resources

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Date:	Wed, 15 Dec 2010 10:27:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Len Brown <lenb@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	linux-acpi@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Adam Belay <abelay@....edu>
Subject: Re: [PATCH 5/5] PNP: HP nx6325 fixup: reserve unreported resources

On 12/15/2010 10:18 AM, Bjorn Helgaas wrote:
> 
> ACPI devices tend to be at high addresses, so allocating top-down
> is definitely more dangerous unless we explicitly avoid them.  I
> should have realized that and done something like patches 1-3 of
> this series before the top-down patches.
> 
> Doing it bottom-up would very likely work better than the "top-down
> without avoiding ACPI regions" model we currently have, at least in
> the short term.  We *would* have to do something to avoid E820
> reservations to fix this:
>   https://bugzilla.kernel.org/show_bug.cgi?id=16228,
> but that's doable.
> 
> So here's my proposal for .37:
>   - Keep the current state of _CRS enabled by default (for 2008
>     and newer machines).
>   - Allocate bottom-up always
>   - Avoid E820 reservations
> 
> That should fix all the regressions I'm aware of.  I'll work on
> the patches this afternoon.
> 

At the same time, I would like to see a few things done as a matter of
course:

a) reserve the top 2 MiB of the 32-bit address space.  There *will* be
ROM at the top of the 32-bit address space; it's a fact of the
architecture, and on at least older systems it was common to have a
shadow 1 MiB below.

b) we may want to consider doing special things in the 0xFExxxxxx memory
range, which is used by the CPU-APIC-MSI system in recent processors.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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