Hi Mark,

I love your patch! Yet something to improve:

[auto build test ERROR on tip/perf/core]
[also build test ERROR on v4.18-rc4 next-20180710]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Mark-Rutland/perf-core-fix-possible-spectre-v1-write/20180711-023735
config: i386-randconfig-x009-201827 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   kernel/events/core.c: In function 'sw_perf_event_destroy':
>> kernel/events/core.c:8158:13: error: implicit declaration of function 'array_index_nospec'; did you mean 'array_index_mask_nospec'? [-Werror=implicit-function-declaration]
     event_id = array_index_nospec(event_id, PERF_COUNT_SW_MAX);
                ^~~~~~~~~~~~~~~~~~
                array_index_mask_nospec
   cc1: some warnings being treated as errors

vim +8158 kernel/events/core.c

  8154	
  8155	static void sw_perf_event_destroy(struct perf_event *event)
  8156	{
  8157		u64 event_id = event->attr.config;
> 8158		event_id = array_index_nospec(event_id, PERF_COUNT_SW_MAX);
  8159	
  8160		WARN_ON(event->parent);
  8161	
  8162		static_key_slow_dec(&perf_swevent_enabled[event_id]);
  8163		swevent_hlist_put();
  8164	}
  8165	

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