83a7a4d643
Arm PMUs can support direct userspace access of counters which allows for low overhead (i.e. no syscall) self-monitoring of tasks. The same feature exists on x86 called 'rdpmc'. Unlike x86, userspace access will only be enabled for thread bound events. This could be extended if needed, but simplifies the implementation and reduces the chances for any information leaks (which the x86 implementation suffers from). PMU EL0 access will be enabled when an event with userspace access is part of the thread's context. This includes when the event is not scheduled on the PMU. There's some additional overhead clearing dirty counters when access is enabled in order to prevent leaking disabled counter data from other tasks. Unlike x86, enabling of userspace access must be requested with a new attr bit: config1:1. If the user requests userspace access with 64-bit counters, then the event open will fail if the h/w doesn't support 64-bit counters. Chaining is not supported with userspace access. The modes for config1 are as follows: config1 = 0 : user access disabled and always 32-bit config1 = 1 : user access disabled and always 64-bit (using chaining if needed) config1 = 2 : user access enabled and always 32-bit config1 = 3 : user access enabled and always 64-bit Based on work by Raphael Gault <raphael.gault@arm.com>, but has been completely re-written. Cc: Will Deacon <will@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-perf-users@vger.kernel.org Signed-off-by: Rob Herring <robh@kernel.org> Link: https://lore.kernel.org/r/20211208201124.310740-5-robh@kernel.org [will: Made armv8pmu_proc_user_access_handler() static] Signed-off-by: Will Deacon <will@kernel.org> |
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| .. | ||
| boot | ||
| configs | ||
| crypto | ||
| hyperv | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| mm | ||
| net | ||
| tools | ||
| xen | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.platforms | ||
| Makefile | ||