perf/x86: Fix RDPMC vs. mm_struct tracking

perf/x86: Fix RDPMC vs. mm_struct tracking

Vince reported the following rdpmc() testcase failure:

 > Failing test case:
 >
 >	fd=perf_event_open();
 >	addr=mmap(fd);
 >	exec()  // without closing or unmapping the event
 >	fd=perf_event_open();
 >	addr=mmap(fd);
 >	rdpmc()	// GPFs due to rdpmc being disabled

The problem is of course that exec() plays tricks with what is
current->mm, only destroying the old mappings after having
installed the new mm.

Fix this confusion by passing along vma->vm_mm instead of relying on
current->mm.

Reported-by: Vince Weaver <[email protected]>
Tested-by: Vince Weaver <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Andy Lutomirski <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Fixes: 1e0fb9ec679c ("perf: Add pmu callbacks to track event mapping and unmapping")
Link: http://lkml.kernel.org/r/[email protected]
[ Minor cleanups. ]
Signed-off-by: Ingo Molnar <[email protected]>