From: Peter Zijlstra Date: Thu, 24 Oct 2013 10:52:06 +0000 (+0200) Subject: perf/x86: Further optimize copy_from_user_nmi() X-Git-Tag: omap-for-v3.13/fixes-for-merge-window-take2~41^2~19 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e00b12e64be9a34ef071de7b6052ca9ea29dd460;p=pandora-kernel.git perf/x86: Further optimize copy_from_user_nmi() 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 Cc: jmario@redhat.com Cc: Arnaldo Carvalho de Melo Cc: Linus Torvalds Cc: Andi Kleen Cc: dave.hansen@linux.intel.com Tested-by: Don Zickus Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131024105206.GM2490@laptop.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed