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Diffstat (limited to 'tools/perf/Documentation/perf-arm-spe.txt')
| -rw-r--r-- | tools/perf/Documentation/perf-arm-spe.txt | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/tools/perf/Documentation/perf-arm-spe.txt b/tools/perf/Documentation/perf-arm-spe.txt index bf03222e9a..0a3eda4823 100644 --- a/tools/perf/Documentation/perf-arm-spe.txt +++ b/tools/perf/Documentation/perf-arm-spe.txt @@ -116,6 +116,15 @@ Depending on CPU model, the kernel may need to be booted with page table isolati (kpti=off). If KPTI needs to be disabled, this will fail with a console message "profiling buffer inaccessible. Try passing 'kpti=off' on the kernel command line". +For the full criteria that determine whether KPTI needs to be forced off or not, see function +unmap_kernel_at_el0() in the kernel sources. Common cases where it's not required +are on the CPUs in kpti_safe_list, or on Arm v8.5+ where FEAT_E0PD is mandatory. + +The SPE interrupt must also be described by the firmware. If the module is loaded and KPTI is +disabled (or isn't required to be disabled) but the SPE PMU still doesn't show in +/sys/bus/event_source/devices/, then it's possible that the SPE interrupt isn't described by +ACPI or DT. In this case no warning will be printed by the driver. + Capturing SPE with perf command-line tools ------------------------------------------ @@ -199,7 +208,8 @@ Common errors - "Cannot find PMU `arm_spe'. Missing kernel support?" - Module not built or loaded, KPTI not disabled (see above), or running on a VM + Module not built or loaded, KPTI not disabled, interrupt not described by firmware, + or running on a VM. See 'Kernel Requirements' above. - "Arm SPE CONTEXT packets not found in the traces." |