Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

H. Peter Anvin
2010-08-04T20:27:08Z

On 08/04/2010 02:46 AM, Peter Zijlstra wrote:
> On Fri, 2010-07-16 at 11:05 -0700, H. Peter Anvin wrote:
>>
>> I really hope noone ever gets the idea of touching user space from an
>> NMI handler, though, and expecting it to work...
>
> Perf actually already does that to unwind user-space stacks... ;-)
>
> See arch/x86/kernel/cpu/perf_event.c:copy_from_user_nmi() and its users.
>
> What we do is a manual page table walk (using __get_user_pages_fast) and
> simply bail when the page is not available.
>

That's not really "touching user space", though.

-hpa