linux-kernel - Re: [patch] x86, pat: fix warn_on_once() while mapping 0-1MB range with /dev/mem

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Date:	Sat, 14 Feb 2009 02:49:05 +0100
From:	Frans Pop <elendil@...net.nl>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, venkatesh.pallipadi@...el.com,
	jeffm@...e.com
Subject: Re: [patch] x86, pat: fix warn_on_once() while mapping 0-1MB range with /dev/mem

Suresh Siddha wrote:
> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: x86, pat: fix warn_on_once() while mapping 0-1MB range
> with /dev/mem
> 
> Jeff Mahoney reported:
>> With Suse's hwinfo tool, on -tip:
>> WARNING: at arch/x86/mm/pat.c:637 reserve_pfn_range+0x5b/0x26d()
> 
> reserve_pfn_range() is not tracking the memory range below 1MB
> as non-RAM and as such is inconsistent with similar checks in
> reserve_memtype() and free_memtype()
> 
> Rename the pagerange_is_ram() to pat_pagerange_is_ram() and add the
> "track legacy 1MB region as non RAM" condition.
> 
> And also, fix reserve_pfn_range() to return -EINVAL, when the pfn
> range is RAM. This is to be consistent with this API design.
> 
> Reported-and-tested-by: Jeff Mahoney <jeffm@...e.com>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>

I've given this patch a try because I've been getting the same warning 
when starting VirtualBox guest machines (VM) and it looked as if this 
might fix that.

With this patch on top of 2.6.29-rc5 the VirtualBox kernel modules build 
and load without errors, but when I try to start a VM I get an error that 
a symbol cannot be found. The VM does start correctly if I boot the 
kernel on the host with "nopat".

I suspect the problem is with VirtualBox, but thought I'd mention it here 
just in case it's an indication of a regression.

Details on the issue can be found here:
http://www.virtualbox.org/ticket/3090

The suddenly missing symbol gets defined here for VBox (lines 217-237):
http://www.virtualbox.org/browser/trunk/include/VBox/sup.h

Host system is debian/lenny/amd64 running x86_64.

Cheers,
FJP
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