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

From: H. Peter Anvin
Date: Wed Aug 04 2010 - 16:27:16 EST

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.

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