linux-kernel - Re: [GIT PULL] x86/uapi for 3.8

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Date:	Mon, 17 Dec 2012 09:04:35 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Matt Fleming" <matt.fleming@...el.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Markus Trippelsdorf" <markus@...ppelsdorf.de>
Cc:	"Arnd Bergmann" <arnd@...db.de>, "Ingo Molnar" <mingo@...e.hu>,
	"Michael Kerrisk" <mtk.manpages@...il.com>,
	"Guennadi Liakhovetski" <g.liakhovetski@....de>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Dave Jones" <davej@...hat.com>,
	"David Howells" <dhowells@...hat.com>,
	"Grant Likely" <grant.likely@...retlab.ca>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86/uapi for 3.8

>>> On 15.12.12 at 19:35, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Sat, Dec 15, 2012 at 8:33 AM, Markus Trippelsdorf
> <markus@...ppelsdorf.de> wrote:
>> On 2012.12.14 at 17:47 -0800, Linus Torvalds wrote:
>>>
>>> Ho humm. Anybody else see anything strange?
>>
>> Yes. I'm seeing a BUG early during boot on my machine (RIP=NULL):
>>
>>  BUG: unable to handle kernel NULL pointer dereference at           (null)
>>
>> This is caused by commit 53b87cf088e2 ("x86, mm: Include the
>> entire kernel memory map in trampoline_pgd")
> 
> Hmm. That reverts cleanly, and the result boots fine for me. And the
> commit looks like exactly the kind of thing that could result in
> problems with exactly the right memory layout, so it could explain why
> the bisect failed and some kernels randomly worked for me and others
> didn't.
> 
> So this at least looks like a very possible candidate.
> 
> Does anybody have an explanation for the problem?

How about this being caused by using the same lower level
page table entries that swapper_pg_dir uses, namely including
the _PAGE_GLOBAL bits? efi_call_virt_{pre,epi}log() only write
CR3 (see 185034e72d591f9465e5e18f937ed642e7ea0070), but
would need to also flip CR4.PGE afaict.

Jan

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