Re: [GIT PULL] x86/uapi for 3.8

[Jan Beulich]

>>> On 15.12.12 at 19:35, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, Dec 15, 2012 at 8:33 AM, Markus Trippelsdorf
> <markus@xxxxxxxxxxxxxxx> 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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