[PATCH v2 0/8] riscv: Support compiling the kernel with more extensions

[Charlie Jenkins]

The kernel currently has the restriction that it can only be compiled
with the extensions that are hardcoded in arch/risc/Makefile.

Any extension that is not listed in the Makefile can still be used by
explicitly writing the assembly and using alternative patching.

This series introduces Kconfig options that allow the kernel to be
compiled with additional extensions.

The motivation for this patch is the performance improvements that come
along with compiling the kernel with these extra instructions. Allowing
the compiler to emit arbitrary Zb* instructions achieves a 4.9%
reduction of dynamic instruction count for a test ran in Spike that
boots the kernel and runs a user space program that prints to the
console.

Additionally, alternatives that check if an extension is supported can
be eliminated when the Kconfig options to assume hardware support is
enabled.

This series is based on the wording changes from Conor in:

https://lore.kernel.org/lkml/20240424-tabby-plural-5f1d9fe44f47@spud/T/

Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
---
Changes in v2:
- Eliminate references to incorrect config in Svpbmt patch (Jess)
- Add motivation to cover letter (Conor)
- Remove "v" from march
- Correct the ifdef for vector
- Correct the ifdef for Svnapot
- Link to v1: https://lore.kernel.org/r/20240506-compile_kernel_with_extensions-v1-0-5c25c134c097@rivosinc.com

---
Charlie Jenkins (8):
      riscv: Add PLATFORM_MAY_SUPPORT_RISCV_ISA_C Kconfig option
      riscv: Add PLATFORM_MAY_SUPPORT_RISCV_ISA_V Kconfig option
      riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT Kconfig option
      riscv: Move RISCV_ISA_SVPBMT to Kconfig.isa
      riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_ZBB Kconfig option
      riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_ZBA Kconfig option
      riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_ZBC Kconfig option
      riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_ZBS Kconfig option

 arch/riscv/Kconfig                    | 133 +-----------
 arch/riscv/Kconfig.isa                | 393 ++++++++++++++++++++++++++++++++++
 arch/riscv/Makefile                   |  14 +-
 arch/riscv/crypto/Kconfig             |  14 +-
 arch/riscv/include/asm/arch_hweight.h |  33 +--
 arch/riscv/include/asm/checksum.h     |  18 +-
 arch/riscv/include/asm/pgtable.h      |   3 +-
 arch/riscv/include/asm/simd.h         |   3 +
 arch/riscv/include/asm/vector.h       |   3 +-
 arch/riscv/kernel/cpufeature.c        |   3 +-
 arch/riscv/kernel/head.S              |   8 +-
 arch/riscv/kernel/probes/uprobes.c    |   2 +-
 arch/riscv/kernel/process.c           |  12 +-
 arch/riscv/kernel/ptrace.c            |   6 +
 arch/riscv/lib/csum.c                 |  48 ++---
 arch/riscv/lib/riscv_v_helpers.c      |   1 -
 arch/riscv/lib/strcmp.S               |   4 +-
 arch/riscv/lib/strlen.S               |   4 +-
 arch/riscv/lib/strncmp.S              |   4 +-
 arch/riscv/lib/uaccess_vector.S       |   2 +
 arch/riscv/lib/xor.S                  |   2 +
 arch/riscv/net/bpf_jit.h              |   8 +-
 22 files changed, 509 insertions(+), 209 deletions(-)
---
base-commit: 2f47357557b7aa98d9d9002688aae480864ca3f6
change-id: 20240429-compile_kernel_with_extensions-92dd2403d325
-- 
- Charlie