linux-kernel - [PATCH 5.13 043/800] arm_pmu: Fix write counter incorrect in ARMv7 big-endian mode

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Date:   Mon, 12 Jul 2021 08:01:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yang Jihong <yangjihong1@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH 5.13 043/800] arm_pmu: Fix write counter incorrect in ARMv7 big-endian mode

From: Yang Jihong <yangjihong1@...wei.com>

commit fdbef8c4e68ad423416aa6cc93d1616d6f8ac5b3 upstream.

Commit 3a95200d3f89 ("arm_pmu: Change API to support 64bit counter values")
changes the input "value" type from 32-bit to 64-bit, which introduces the
following problem: ARMv7 PMU counters is 32-bit width, in big-endian mode,
write counter uses high 32-bit, which writes an incorrect value.

Before:

 Performance counter stats for 'ls':

              2.22 msec task-clock                #    0.675 CPUs utilized
                 0      context-switches          #    0.000 K/sec
                 0      cpu-migrations            #    0.000 K/sec
                49      page-faults               #    0.022 M/sec
        2150476593      cycles                    #  966.663 GHz
        2148588788      instructions              #    1.00  insn per cycle
        2147745484      branches                  # 965435.074 M/sec
        2147508540      branch-misses             #   99.99% of all branches

None of the above hw event counters are correct.

Solution:

"value" forcibly converted to 32-bit type before being written to PMU register.

After:

 Performance counter stats for 'ls':

              2.09 msec task-clock                #    0.681 CPUs utilized
                 0      context-switches          #    0.000 K/sec
                 0      cpu-migrations            #    0.000 K/sec
                46      page-faults               #    0.022 M/sec
           2807301      cycles                    #    1.344 GHz
           1060159      instructions              #    0.38  insn per cycle
            250496      branches                  #  119.914 M/sec
             23192      branch-misses             #    9.26% of all branches

Fixes: 3a95200d3f89 ("arm_pmu: Change API to support 64bit counter values")
Cc: <stable@...r.kernel.org>
Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
Acked-by: Mark Rutland <mark.rutland@....com>
Link: https://lore.kernel.org/r/20210430012659.232110-1-yangjihong1@huawei.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/kernel/perf_event_v7.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -773,10 +773,10 @@ static inline void armv7pmu_write_counte
 		pr_err("CPU%u writing wrong counter %d\n",
 			smp_processor_id(), idx);
 	} else if (idx == ARMV7_IDX_CYCLE_COUNTER) {
-		asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" (value));
+		asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" ((u32)value));
 	} else {
 		armv7_pmnc_select_counter(idx);
-		asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" (value));
+		asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" ((u32)value));
 	}
 }