[PATCH v10 0/2] riscv: Create and document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl

[Charlie Jenkins]

Improve the performance of icache flushing by creating a new prctl flag
PR_RISCV_SET_ICACHE_FLUSH_CTX. The interface is left generic to allow
for future expansions such as with the proposed J extension [1].

Documentation is also provided to explain the use case.

Patch sent to add PR_RISCV_SET_ICACHE_FLUSH_CTX to man-pages [2].

[1] https://github.com/riscv/riscv-j-extension
[2] https://lore.kernel.org/linux-man/20240124-fencei_prctl-v1-1-0bddafcef331@xxxxxxxxxxxx

Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
---
Changes in v10:
- Fix fence.i condition to properly only flush on migration (Alex)
- Fix documentation wording (Alex)
- Link to v9: https://lore.kernel.org/r/20240123-fencei-v9-0-71411bfe8d71@xxxxxxxxxxxx

Changes in v9:
- Remove prev_cpu from mm (Alex)
- Link to v8: https://lore.kernel.org/r/20240116-fencei-v8-0-43a42134f021@xxxxxxxxxxxx

Changes in v8:
- Only flush icache if migrated to different cpu (Alex)
- Move flushing to switch_to to catch per-thread flushing properly
- Link to v7: https://lore.kernel.org/r/20240112-fencei-v7-0-78f0614e1db0@xxxxxxxxxxxx

Changes in v7:
- Change "per_thread" parameter to "scope" and provide constants for the
  parameter.
- Link to v6: https://lore.kernel.org/r/20240109-fencei-v6-0-04116e51445c@xxxxxxxxxxxx

Changes in v6:
- Fixup documentation formatting
- Link to v5: https://lore.kernel.org/r/20240108-fencei-v5-0-aa1e51d7222f@xxxxxxxxxxxx

Changes in v5:
- Minor documentation changes (Randy)
- Link to v4: https://lore.kernel.org/r/20240107-fencei-v4-0-d4cf2fb905d3@xxxxxxxxxxxx

Changes in v4:
- Add OFF flag to disallow fence.i in userspace (Atish)
- Fix documentation issues (Atish)
- Link to v3: https://lore.kernel.org/r/20231213-fencei-v3-0-b75158238eb7@xxxxxxxxxxxx

Changes in v3:
- Check if value force_icache_flush set on thread, rather than in mm
  twice (Clément)
- Link to v2: https://lore.kernel.org/r/20231130-fencei-v2-0-2cb623ab1b1f@xxxxxxxxxxxx

Changes in v2:
- Fix kernel-doc comment (Conor)
- Link to v1: https://lore.kernel.org/r/20231122-fencei-v1-0-bec0811cb212@xxxxxxxxxxxx

---
Charlie Jenkins (2):
      riscv: Include riscv_set_icache_flush_ctx prctl
      documentation: Document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl

 Documentation/arch/riscv/cmodx.rst | 96 ++++++++++++++++++++++++++++++++++++++
 Documentation/arch/riscv/index.rst |  1 +
 arch/riscv/include/asm/mmu.h       |  2 +
 arch/riscv/include/asm/processor.h |  7 +++
 arch/riscv/include/asm/switch_to.h | 13 ++++++
 arch/riscv/mm/cacheflush.c         | 67 ++++++++++++++++++++++++++
 arch/riscv/mm/context.c            | 13 ++++--
 include/uapi/linux/prctl.h         |  6 +++
 kernel/sys.c                       |  6 +++
 9 files changed, 208 insertions(+), 3 deletions(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20231117-fencei-f9f60d784fa0
-- 
- Charlie