[PATCH v4 00/10] riscv: Allow userspace to directly access perf counters

Alexandre Ghiti
2023-07-27T14:14:36Z

riscv used to allow direct access to cycle/time/instret counters,
bypassing the perf framework, this patchset intends to allow the user to
mmap any counter when accessed through perf.

**Important**: The default mode is now user access through perf only, not
the legacy so some applications will break. However, we introduce a sysctl
perf_user_access like arm64 does, which will allow to switch to the legacy
mode described above.

This version needs openSBI v1.3 *and* a kernel fix that went upstream lately
(https://lore.kernel.org/lkml/20230616114831.3186980-1-maz@kernel.org/T/).

base-commit-tag: v6.5-rc1

Changes in v5:
- Fix typo from Atish
- Add RB from Atish and Andrew
- Improve cover letter and patch 7 commit log to explain why we made the
choice to break userspace for security reasons, thanks Atish and Rémi
- Rebase on top of v6.5-rc1

Changes in v4:
- Fixed some nits in riscv_pmu_sbi.c thanks to Andrew
- Fixed the documentation thanks to Andrew
- Added RB from Andrew \o/

Changes in v3:
- patch 1 now contains the ref to the faulty commit (no Fixes tag as it is only a comment), as Andrew suggested
- Removed RISCV_PMU_LEGACY_TIME from patch 3, as Andrew suggested
- Rename RISCV_PMU_PDEV_NAME to "riscv-pmu-sbi", patch4 is just cosmetic now, as Andrew suggested
- Removed a few useless (and wrong) comments, as Andrew suggested
- Simplify arch_perf_update_userpage code, as Andrew suggested
- Documentation now mentions that time CSR is *always* accessible, whatever the mode, as suggested by Andrew
- Removed CYCLEH reference and add TODO for rv32 support, as suggested by Atish
- Do not rename the pmu instance as Atish suggested
- Set pmc_width only if rdpmc is enabled and CONFIG_RISCV_PMU is set and the event is a hw event
- Move arch_perf_update_userpage https://lore.kernel.org/lkml/20230616114831.3186980-1-maz@kernel.org/T/
- **Switch to user mode access by default**

Changes in v2:
- Split into smaller patches, way better!
- Add RB from Conor
- Simplify the way we checked riscv architecture
- Fix race mmap and other thread running on other cpus
- Use hwc when available
- Set all userspace access flags in event_init, too cumbersome to handle sysctl changes
- Fix arch_perf_update_userpage for pmu other than riscv-pmu by renaming pmu driver
- Fixed kernel test robot build error
- Fixed documentation (Andrew and Bagas)
- perf testsuite passes mmap tests in all 3 modes

Alexandre Ghiti (10):
perf: Fix wrong comment about default event_idx
include: riscv: Fix wrong include guard in riscv_pmu.h
riscv: Make legacy counter enum match the HW numbering
drivers: perf: Rename riscv pmu sbi driver
riscv: Prepare for user-space perf event mmap support
drivers: perf: Implement perf event mmap support in the legacy backend
drivers: perf: Implement perf event mmap support in the SBI backend
Documentation: admin-guide: Add riscv sysctl_perf_user_access
tools: lib: perf: Implement riscv mmap support
perf: tests: Adapt mmap-basic.c for riscv

Documentation/admin-guide/sysctl/kernel.rst | 27 ++-
drivers/perf/riscv_pmu.c | 113 +++++++++++
drivers/perf/riscv_pmu_legacy.c | 28 ++-
drivers/perf/riscv_pmu_sbi.c | 196 +++++++++++++++++++-
include/linux/perf/riscv_pmu.h | 12 +-
include/linux/perf_event.h | 3 +-
tools/lib/perf/mmap.c | 65 +++++++
tools/perf/tests/mmap-basic.c | 4 +-
8 files changed, 428 insertions(+), 20 deletions(-)

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2.39.2