Re: frequent lockups in 3.18rc4

From: Andy Lutomirski
Date: Fri Nov 21 2014 - 12:30:26 EST

On Fri, Nov 21, 2014 at 9:19 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Nov 21, 2014 at 9:08 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>> Actually, in_nmi() is now safe for vmalloc faults. In fact, it handles the
>> clobbering of the cr2 register just fine.
> That's not what I object to and find incorrect wrt NMI.
> Compare the simple and correct 32-bit code to the complex and
> incorrect 64-bit code.
> In particular, look at how the 32-bit code relies *entirely* on hardware state.
> Then look at where the 64-bit code does not.

Both mystify me. Why does the 32-bit version walk down the hierarchy
at all instead of just touching the top level?

And why does the 64-bit version assert that the leaves of the tables
match? It's already asserted that it's walking down pgd pointers that
are *exactly the same pointers*, so of course the stuff they point to
is the same.

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