BACKPORT: arm64: errata: add detection for AMEVCNTR01 incrementing incorrectly
The AMU counter AMEVCNTR01 (constant counter) should increment at the same
rate as the system counter. On affected Cortex-A510 cores, AMEVCNTR01
increments incorrectly giving a significantly higher output value. This
results in inaccurate task scheduler utilization tracking and incorrect
feedback on CPU frequency.
Work around this problem by returning 0 when reading the affected counter
in key locations that results in disabling all users of this counter from
using it either for frequency invariance or as FFH reference counter. This
effect is the same to firmware disabling affected counters.
Details on how the two features are affected by this erratum:
- AMU counters will not be used for frequency invariance for affected
CPUs and CPUs in the same cpufreq policy. AMUs can still be used for
frequency invariance for unaffected CPUs in the system. Although
unlikely, if no alternative method can be found to support frequency
invariance for affected CPUs (cpufreq based or solution based on
platform counters) frequency invariance will be disabled. Please check
the chapter on frequency invariance at
Documentation/scheduler/sched-capacity.rst for details of its effect.
- Given that FFH can be used to fetch either the core or constant counter
values, restrictions are lifted regarding any of these counters
returning a valid (!0) value. Therefore FFH is considered supported
if there is a least one CPU that support AMUs, independent of any
counters being disabled or affected by this erratum. Clarifying
comments are now added to the cpc_ffh_supported(), cpu_read_constcnt()
and cpu_read_corecnt() functions.
The above is achieved through adding a new erratum: ARM64_ERRATUM_2457168.
Bug: 293828185
Bug: 297132017
Bug: 297158823
(cherry picked from commit e084c6ab37d2bbd2fca0e993ffe0a308fe407f6c)
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20220819103050.24211-1-ionela.voinescu@arm.com
Change-Id: I167b8a044127c5d24e3b9bd5d43cee28a9abc305
Signed-off-by: Han Lin <han.lin@mediatek.com>
Signed-off-by: Keir Fraser <keirf@google.com>
(cherry picked from commit d2351ceb4c61c7e0e6f64e96277bbc4715b74083)
diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
index 9602586..d585096 100644
--- a/Documentation/arm64/silicon-errata.rst
+++ b/Documentation/arm64/silicon-errata.rst
@@ -102,6 +102,8 @@
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-A710 | #2224489 | ARM64_ERRATUM_2224489 |
+----------------+-----------------+-----------------+-----------------------------+
+| ARM | Cortex-A510 | #2457168 | ARM64_ERRATUM_2457168 |
++----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N1 | #1188873,1418040| ARM64_ERRATUM_1418040 |
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N1 | #1349291 | N/A |
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9d8b5c8..074017c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -819,6 +819,23 @@
If unsure, say Y.
+config ARM64_ERRATUM_2457168
+ bool "Cortex-A510: 2457168: workaround for AMEVCNTR01 incrementing incorrectly"
+ depends on ARM64_AMU_EXTN
+ default y
+ help
+ This option adds the workaround for ARM Cortex-A510 erratum 2457168.
+
+ The AMU counter AMEVCNTR01 (constant counter) should increment at the same rate
+ as the system counter. On affected Cortex-A510 cores AMEVCNTR01 increments
+ incorrectly giving a significantly higher output value.
+
+ Work around this problem by returning 0 when reading the affected counter in
+ key locations that results in disabling all users of this counter. This effect
+ is the same to firmware disabling affected counters.
+
+ If unsure, say Y.
+
config CAVIUM_ERRATUM_22375
bool "Cavium erratum 22375, 24313"
default y
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 1f177fd..1685d17 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -545,6 +545,15 @@
CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
},
#endif
+#ifdef CONFIG_ARM64_ERRATUM_2457168
+ {
+ .desc = "ARM erratum 2457168",
+ .capability = ARM64_WORKAROUND_2457168,
+ .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
+ /* Cortex-A510 r0p0-r1p1 */
+ CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1)
+ },
+#endif
{
}
};
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6b73253..eb6f87d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1701,7 +1701,10 @@
pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n",
smp_processor_id());
cpumask_set_cpu(smp_processor_id(), &amu_cpus);
- update_freq_counters_refs();
+
+ /* 0 reference values signal broken/disabled counters */
+ if (!this_cpu_has_cap(ARM64_WORKAROUND_2457168))
+ update_freq_counters_refs();
}
}
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index e9af726..877c68f 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -268,12 +268,25 @@
static void cpu_read_corecnt(void *val)
{
+ /*
+ * A value of 0 can be returned if the current CPU does not support AMUs
+ * or if the counter is disabled for this CPU. A return value of 0 at
+ * counter read is properly handled as an error case by the users of the
+ * counter.
+ */
*(u64 *)val = read_corecnt();
}
static void cpu_read_constcnt(void *val)
{
- *(u64 *)val = read_constcnt();
+ /*
+ * Return 0 if the current CPU is affected by erratum 2457168. A value
+ * of 0 is also returned if the current CPU does not support AMUs or if
+ * the counter is disabled. A return value of 0 at counter read is
+ * properly handled as an error case by the users of the counter.
+ */
+ *(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_2457168) ?
+ 0UL : read_constcnt();
}
static inline
@@ -300,7 +313,22 @@
*/
bool cpc_ffh_supported(void)
{
- return freq_counters_valid(get_cpu_with_amu_feat());
+ int cpu = get_cpu_with_amu_feat();
+
+ /*
+ * FFH is considered supported if there is at least one present CPU that
+ * supports AMUs. Using FFH to read core and reference counters for CPUs
+ * that do not support AMUs, have counters disabled or that are affected
+ * by errata, will result in a return value of 0.
+ *
+ * This is done to allow any enabled and valid counters to be read
+ * through FFH, knowing that potentially returning 0 as counter value is
+ * properly handled by the users of these counters.
+ */
+ if ((cpu >= nr_cpu_ids) || !cpumask_test_cpu(cpu, cpu_present_mask))
+ return false;
+
+ return true;
}
int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val)
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 4de5056..7119b55 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -27,7 +27,7 @@
HAS_LSE_ATOMICS
HAS_NO_FPSIMD
# HAS_NO_HW_PREFETCH
-ANDROID_RESERVED_1
+WORKAROUND_2457168
HAS_PAN
HAS_RAS_EXTN
HAS_RNG
