Re: [PATCH 0/3] unified way to use static key and optimize pgtable_l4_enabled

[Palmer Dabbelt]

On Tue, 25 Jan 2022 08:50:33 PST (-0800), jszhang@xxxxxxxxxx wrote:
> Currently, riscv has several features why may not be supported on all
> riscv platforms, for example, FPU, SV48 and so on. To support unified
> kernel Image style, we need to check whether the feature is suportted
> or not. If the check sits at hot code path, then performance will be
> impacted a lot. static key can be used to solve the issue. In the
> past FPU support has been converted to use static key mechanism. I
> believe we will have similar cases in the future. For example, the
> SV48 support can take advantage of static key[1].
>
> patch1 introduces an unified mechanism to use static key for riscv cpu
> features.
> patch2 converts has_cpu() to use the mechanism.
> patch3 uses the mechanism to optimize pgtable_l4_enabled.
>
> [1] http://lists.infradead.org/pipermail/linux-riscv/2021-December/011164.html
>
> Jisheng Zhang (3):
>   riscv: introduce unified static key mechanism for CPU features
>   riscv: replace has_fpu() with system_supports_fpu()
>   riscv: convert pgtable_l4_enabled to static key

I see some build failures from LKP, but I don't see a v2.  LMK if I 
missed it.

>  arch/riscv/Makefile                 |   3 +
>  arch/riscv/include/asm/cpufeature.h | 105 ++++++++++++++++++++++++++++
>  arch/riscv/include/asm/pgalloc.h    |   8 +--
>  arch/riscv/include/asm/pgtable-64.h |  21 +++---
>  arch/riscv/include/asm/pgtable.h    |   3 +-
>  arch/riscv/include/asm/switch_to.h  |   9 +--
>  arch/riscv/kernel/cpu.c             |   2 +-
>  arch/riscv/kernel/cpufeature.c      |  29 ++++++--
>  arch/riscv/kernel/process.c         |   2 +-
>  arch/riscv/kernel/signal.c          |   4 +-
>  arch/riscv/mm/init.c                |  23 +++---
>  arch/riscv/mm/kasan_init.c          |   6 +-
>  arch/riscv/tools/Makefile           |  22 ++++++
>  arch/riscv/tools/cpucaps            |   6 ++
>  arch/riscv/tools/gen-cpucaps.awk    |  40 +++++++++++
>  15 files changed, 234 insertions(+), 49 deletions(-)
>  create mode 100644 arch/riscv/include/asm/cpufeature.h
>  create mode 100644 arch/riscv/tools/Makefile
>  create mode 100644 arch/riscv/tools/cpucaps
>  create mode 100755 arch/riscv/tools/gen-cpucaps.awk