linux-kernel - Re: ohci1394_dma=early crash since 2.6.32 (was Re: [Bug #14487] PANIC: early exception 08 rip 246:10 error ffffffff810251b5 cr2 0)

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Message-Id: <4B694D5C020000780002D6DA@vpn.id2.novell.com>
Date:	Wed, 03 Feb 2010 09:18:04 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Justin P. Mattock" <justinmattock@...il.com>,
	"Stefan Richter" <stefanr@...6.in-berlin.de>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Dan Carpenter" <error27@...il.com>,
	<bernhard.kaindl@....net>, "Thomas Gleixner" <tglx@...utronix.de>,
	<linux1394-devel@...ts.sourceforge.net>,
	"Rafael Wysocki" <rjw@...k.pl>,
	"Kernel Testers List" <kernel-testers@...r.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	<ebiderman@...ssion.com>, <hpa@...or.com>
Subject: Re: ohci1394_dma=early crash since 2.6.32 (was Re: [Bug
	 #14487] PANIC: early exception 08 rip 246:10
	 error	ffffffff810251b5 cr2 0)

>>> "Justin P. Mattock" <justinmattock@...il.com> 03.02.10 02:43 >>>
>The only thing I can think of at this point
>is maybe the CFLAGS I used to build this system.
>(as for the x86_32 working and x86_64 failing not sure);
>
>I'm curious to see if anybody else is hitting this?

I think it is pretty clear how a page fault can happen here (but you're
observing a double fault, which I cannot explain [nor can I explain
why the fault apparently didn't get an error code pushed, which is
why address and error code displayed are mixed up]): I would
suspect that FIX_OHCI1394_BASE is now in a different (virtual) 2Mb
range than what is covered by level{1,2}_fixmap_pgt, but this was
a latent issue even before that patch (just waiting for sufficiently
many fixmap entries getting inserted before
__end_of_permanent_fixed_addresses).

The thing is that head_64.S uses hard-coded numbers, but doesn't 
really make sure (at build time) that the fixmap page tables established
indeed cover all the entries of importance (and honestly I even can't
easily tell which of the candidates - FIX_DBGP_BASE,
FIX_EARLYCON_MEM_BASE, and FIX_OHCI1394_BASE afaict - really
matter). If either of the first does, the only reasonable solution imo
is to move FIX_OHCI1394_BASE out of the boot time only range into
the permanent range (unless the other two can be moved into the
boot time only range). And obviously the hard coded numbers
should be eliminated from head_64.S.

Jan

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