Re: Regression in 2.6.23-pre Was: Problems with 2.6.23-rc6 onAMD Geode LX800

From: Jordan Crouse
Date: Wed Sep 26 2007 - 11:42:10 EST

On 26/09/07 07:10 -0700, H. Peter Anvin wrote:
> Joerg Pommnitz wrote:
> > Hello all,
> > this is what git bisect told me about the problem:
> >
> > jpo@jpo-laptop:~/linux-2.6$ git bisect good
> > 4fd06960f120e02e9abc802a09f9511c400042a5 is first bad commit
> > commit 4fd06960f120e02e9abc802a09f9511c400042a5
> > Author: H. Peter Anvin <hpa@xxxxxxxxx>
> > Date: Wed Jul 11 12:18:56 2007 -0700
> >
> > Use the new x86 setup code for i386
> >
> > This patch hooks the new x86 setup code into the Makefile machinery. It
> > also adapts boot/tools/build.c to a two-file (as opposed to three-file)
> > universe, and simplifies it substantially.
> >
> > Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> >
> > :040000 040000 6560eb5b7e40d93813276544bced8c478f9067f5 fe5f90d9ca08e526559815789175602ba2c51743 M arch
> >
> There is something very fishy.
> The only documentation you've given us so far is a screen shot which
> contained a message ("BIOS data check successful") which doesn't occur
> in the kernel.
> The loader string doesn't look all that familiar either; it looks like
> an extremely old version of SYSLINUX, but that doesn't contain that
> message either.
> INT 6 is #UD, the undefined instruction exception. This is consistent with:
> > Its hitting a bug - specifically (from bootmem.c:125):
> > BUG_ON(PFN_DOWN(addr) >= bdata->node_low_pfn);
> However, all that tells us is that reserve_bootmem_core() was either
> called with a bad address or bdata->node_low_pfn is garbage. In
> particular, without knowing how it got there it's hard to know for sure.

/me swings a +5 JTAG debugger

Its the latter - max_pfn as read by find_max_pfn() in arch/i386/e820.c
is being set to 9F (640k) in the broken case, this due to the
the e820 map looking something like this:

Address Size Type
00000000 0009FC00 1
0009FC00 00000400 2
000E0000 00002000 2

(Yep, thats it - thats the list. e820.nr_map is indeed 3).

Long story short, bdata->node_low_pfn gets set to 9F, and When we
try to allocate the bootmem bitmap (at _pa_symbol(_text), which is
page 0x100), then the system gets appropriately angry.

As background, I'm using syslinux 3.36 as my loader here - I've used this
exact same version for a very long time, so I don't blame it in the least.
Something is getting confused in the early kernel, and whatever that
something is, a still unknown change in a newer version of the BIOS
fixed it. The search goes on.

Jordan Crouse
Systems Software Development Engineer
Advanced Micro Devices, Inc.

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