[PATCH v8 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.

[1] https://github.com/riscv/riscv-j-extension

Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
---
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@rivosinc.com

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@rivosinc.com

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

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

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@rivosinc.com

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@rivosinc.com

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

---
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         |  4 ++
 arch/riscv/include/asm/mmu_context.h |  3 ++
 arch/riscv/include/asm/processor.h   |  7 +++
 arch/riscv/include/asm/switch_to.h   | 17 +++++++
 arch/riscv/mm/cacheflush.c           | 67 +++++++++++++++++++++++++
 arch/riscv/mm/context.c              | 14 ++++--
 include/uapi/linux/prctl.h           |  6 +++
 kernel/sys.c                         |  6 +++
 10 files changed, 218 insertions(+), 3 deletions(-)
---
base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86
change-id: 20231117-fencei-f9f60d784fa0
-- 
- Charlie