powerpc/mm: Add trace point for tracking hash pte fault

This enables us to understand how many hash fault we are taking
when running benchmarks.

For ex:
-bash-4.2# ./perf stat -e  powerpc:hash_fault -e page-faults /tmp/ebizzy.ppc64 -S 30  -P -n 1000
...

 Performance counter stats for '/tmp/ebizzy.ppc64 -S 30 -P -n 1000':

       1,10,04,075      powerpc:hash_fault
       1,10,03,429      page-faults

      30.865978991 seconds time elapsed

NOTE:
The impact of the tracepoint was not noticeable when running test. It was
within the run-time variance of the test. For ex:

without-patch:
--------------

 Performance counter stats for './a.out 3000 300':

	       643      page-faults               #    0.089 M/sec
	  7.236562      task-clock (msec)         #    0.928 CPUs utilized
	 2,179,213      stalled-cycles-frontend   #    0.00% frontend cycles idle
	17,174,367      stalled-cycles-backend    #    0.00% backend  cycles idle
		 0      context-switches          #    0.000 K/sec

       0.007794658 seconds time elapsed

And with-patch:
---------------

 Performance counter stats for './a.out 3000 300':

	       643      page-faults               #    0.089 M/sec
	  7.233746      task-clock (msec)         #    0.921 CPUs utilized
		 0      context-switches          #    0.000 K/sec

       0.007854876 seconds time elapsed

 Performance counter stats for './a.out 3000 300':

	       643      page-faults               #    0.087 M/sec
	       649      powerpc:hash_fault        #    0.087 M/sec
	  7.430376      task-clock (msec)         #    0.938 CPUs utilized
	 2,347,174      stalled-cycles-frontend   #    0.00% frontend cycles idle
	17,524,282      stalled-cycles-backend    #    0.00% backend  cycles idle
		 0      context-switches          #    0.000 K/sec

       0.007920284 seconds time elapsed
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/trace.h

@@ -144,6 +144,26 @@ TRACE_EVENT_FN(opal_exit,
 );
 #endif
 
+TRACE_EVENT(hash_fault,
+
+	    TP_PROTO(unsigned long addr, unsigned long access, unsigned long trap),
+	    TP_ARGS(addr, access, trap),
+	    TP_STRUCT__entry(
+		    __field(unsigned long, addr)
+		    __field(unsigned long, access)
+		    __field(unsigned long, trap)
+		    ),
+
+	    TP_fast_assign(
+		    __entry->addr = addr;
+		    __entry->access = access;
+		    __entry->trap = trap;
+		    ),
+
+	    TP_printk("hash fault with addr 0x%lx and access = 0x%lx trap = 0x%lx",
+		      __entry->addr, __entry->access, __entry->trap)
+);
+
 #endif /* _TRACE_POWERPC_H */
 
 #undef TRACE_INCLUDE_PATH

arch/powerpc/mm/hash_utils_64.c

@@ -57,6 +57,7 @@
 #include <asm/fadump.h>
 #include <asm/firmware.h>
 #include <asm/tm.h>
+#include <asm/trace.h>
 
 #ifdef DEBUG
 #define DBG(fmt...) udbg_printf(fmt)
@@ -1004,6 +1005,7 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
 
 	DBG_LOW("hash_page(ea=%016lx, access=%lx, trap=%lx\n",
 		ea, access, trap);
+	trace_hash_fault(ea, access, trap);
 
 	/* Get region & vsid */
  	switch (REGION_ID(ea)) {