linux-kernel - Re: [PATCH] x86/PCI: never allocate PCI space from the last 1M below 4G

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Date:	Mon, 29 Nov 2010 14:10:25 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH] x86/PCI: never allocate PCI space from the last 1M below
 4G

On 11/29/2010 02:04 PM, Bjorn Helgaas wrote:
>>
>>> We might still want a patch like this current one because it could
>>> work around some BIOS defects, and because I think it's too late to
>>> fix the ACPI resource problem for .37.  But I'm not convinced we
>>> should reserve more than Windows does, because that may keep us from
>>> discovering other important Linux problems.
>>
>> I'm not so sure about that... it feels like a pretty weak argument that
>> we might work on some machines even though our code isn't perfect.
> 
> I think we're talking about whether to reserve the top 1MB or top 2MB.
> I freely admit I don't know the right answer.  My point is merely that
> since we're using a heuristic anyway, copying Windows is a pretty good
> starting point.  In my mind, doing something different requires a
> stronger argument than "it might fix some machines where Windows is
> broken."
> 

Of course.  I did, however, point out the reason *why* in this case:
there are a lot of platforms known (including quite probably *ALL*
pre-E820 systems) to decode 2 MiB for the ROM, due to A20 masking.
Windows doesn't care about those older systems.

	-hpa
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