[PATCH 5.14 020/432] powerpc/perf/hv-gpci: Fix counter value parsing

Greg Kroah-Hartman
2021-09-16T17:21:44Z

From: Kajol Jain <kjain@linux.ibm.com>

commit f9addd85fbfacf0d155e83dbee8696d6df5ed0c7 upstream.

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 fields is counter offset and width of the
counter data returned.

Counter data are returned in a unsigned char array in big endian byte
order. To get the final counter data, the values must 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 and also assumed little endian order. Because of that, hcall
counters values are reported incorrectly.

In particular this can lead to counters go backwards which messes up the
counter prev vs now calculation and leads to huge counter value
reporting:

#: 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/

Fix the shifting logic to correct match the format, ie. read bytes in
big endian order.

Fixes: e4f226b1580b ("powerpc/perf/hv-gpci: Increase request buffer size")
Cc: stable@vger.kernel.org # v4.6+
Reported-by: Nageswara R Sastry<rnsastry@linux.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Tested-by: Nageswara R Sastry<rnsastry@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210813082158.429023-1-kjain@linux.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/perf/hv-gpci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -175,7 +175,7 @@ static unsigned long single_gpci_request
*/
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;