[PATCH] powerpc/perf/hv-gpci: Fix the logic to compute counter value from the hcall result buffer.

[Kajol Jain]

H_GetPerformanceCounterInfo (0xF080) hcall returns the counter data in the
result buffer. Result buffer has specific format defined in the PAPR
specification. One of the field is counter offset and width of the counter
data returned.

Counter data are returned in a unsigned char array. To
get the final counter data, these values should be left shifted
byte at a time. But commit 220a0c609ad17 ("powerpc/perf: Add support 
for the hv gpci (get performance counter info) interface") made the
shifting bitwise. Because of this, hcall counters values could end up
in lower side, which messes the counter prev vs now calculation. This
lead to huge counter value reporting

[command]#: perf stat -e hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
           -C 0 -I 1000
        time             counts unit events
     1.000078854 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     2.000213293                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     3.000320107                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     4.000428392                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     5.000537864                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     6.000649087                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     7.000760312                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     8.000865218             16,448      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
     9.000978985 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
    10.001088891             16,384      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
    11.001201435                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
    12.001307937 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/

Patch here fixes the shifting logic to make is byte-wise with which no more the issue seen. 

Fixes: e4f226b1580b3 ("powerpc/perf/hv-gpci: Increase request buffer size")
Reported-by: Nageswara R Sastry<rnsastry at linux.ibm.com>
Signed-off-by: Kajol Jain <kjain at linux.ibm.com>
---
 arch/powerpc/perf/hv-gpci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index d48413e28c39..c756228a081f 100644
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -175,7 +175,7 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
 	 */
 	count = 0;
 	for (i = offset; i < offset + length; i++)
-		count |= arg->bytes[i] << (i - offset);
+		count |= (u64)(arg->bytes[i]) << ((length - 1 - (i - offset)) * 8);
 
 	*value = count;
 out:
-- 
2.26.2