Re: [patch 1/2] x86_64 page fault NMI-safe

H. Peter Anvin
2010-07-15T22:26:25Z

On 07/15/2010 03:16 PM, Linus Torvalds wrote:
>
>> This code assumes NMIs have a separate stack.
>
> It also needs to be made per-cpu (and the flags be per-cpu).
>
> Then you could in fact possibly test the stack pointer for whether it
> is in the NMI stack area, and use the value of %rsp itself as the
> flag. So you could avoid the flag entirely. Because testing %rsp is
> valid - testing %rip is not.
>
> That would also avoid the race, because %rsp (as a flag) now gets
> cleared atomically by the "iret". So that might actually solve things.
>

This seems really clean to me.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.