Re: [PATCH] perf/x86: Further optimize copy_from_user_nmi()

[Peter Zijlstra <peterz@infradead.org>]

On Tue, May 19, 2015 at 12:08:39PM +0800, Zhiqiang Zhang wrote:
> commit e00b12e64be9a34ef071de7b6052ca9ea29dd460 upstream
> 
> Now that we can deal with nested NMI due to IRET re-enabling NMIs and
> can deal with faults from NMI by making sure we preserve CR2 over NMIs
> we can in fact simply access user-space memory from NMI context.
> 
> So rewrite copy_from_user_nmi() to use __copy_from_user_inatomic() and
> rework the fault path to do the minimal required work before taking
> the in_atomic() fault handler.
> 
> In particular avoid perf_sw_event() which would make perf recurse on
> itself (it should be harmless as our recursion protections should be
> able to deal with this -- but why tempt fate).
> 
> Also rename notify_page_fault() to kprobes_fault() as that is a much
> better name; there is no notifier in it and its specific to kprobes.
> 
> Don measured that his worst case NMI path shrunk from ~300K cycles to
> ~150K cycles.
> 
> Cc: Stephane Eranian <eranian@google.com>
> Cc: jmario@redhat.com
> Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: dave.hansen@linux.intel.com
> Tested-by: Don Zickus <dzickus@redhat.com>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Link: http://lkml.kernel.org/r/20131024105206.GM2490@laptop.programming.kicks-ass.net
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> [zhangzhiqiang: backport to 3.10:

Did you make sure all the nested NMI fixes are in 3.10?