[PATCH v4 0/2] use static key to optimize pgtable_l4_enabled

[Palmer Dabbelt]

On Sat, 25 Jun 2022 21:33:07 PDT (-0700), anup at brainfault.org wrote:
> On Sat, May 21, 2022 at 8:13 PM Jisheng Zhang <jszhang at kernel.org> wrote:
>>
>> The pgtable_l4|[l5]_enabled check sits at hot code path, performance
>> is impacted a lot. Since pgtable_l4|[l5]_enabled isn't changed after
>> boot, so static key can be used to solve the performance issue[1].
>>
>> An unified way static key was introduced in [2], but it only targets
>> riscv isa extension. We dunno whether SV48 and SV57 will be considered
>> as isa extension, so the unified solution isn't used for
>> pgtable_l4[l5]_enabled now.
>>
>> patch1 fixes a NULL pointer deference if static key is used a bit earlier.
>> patch2 uses the static key to optimize pgtable_l4|[l5]_enabled.
>>
>> [1] http://lists.infradead.org/pipermail/linux-riscv/2021-December/011164.html
>> [2] https://lore.kernel.org/linux-riscv/20220517184453.3558-1-jszhang@kernel.org/T/#t
>>
>> Since v3:
>>  - fix W=1 call to undeclared function 'static_branch_likely' error
>>
>> Since v2:
>>  - move the W=1 warning fix to a separate patch
>>  - move the unified way to use static key to a new patch series.
>>
>> Since v1:
>>  - Add a W=1 warning fix
>>  - Fix W=1 error
>>  - Based on v5.18-rcN, since SV57 support is added, so convert
>>    pgtable_l5_enabled as well.
>>
>>
>>
>> Jisheng Zhang (2):
>>   riscv: move sbi_init() earlier before jump_label_init()
>>   riscv: turn pgtable_l4|[l5]_enabled to static key for RV64
>
> I have tested both these patches on QEMU RV64 and RV32.
>
> Tested-by: Anup Patel <anup at brainfault.org>
>
> Thanks,
> Anup

Thanks for testing these.  Unfortunatly they're failing for me under my 
kasan+sparsemem-vmemmap config, which looks like a defconfig with

    CONFIG_KASAN=y
    # CONFIG_FLATMEM_MANUAL is not set
    CONFIG_SPARSEMEM_MANUAL=y
    CONFIG_SPARSEMEM=y
    # CONFIG_SPARSEMEM_VMEMMAP is not set

Nothing's really jumping out and I'm not sure that's a super compelling 
configuration, but IIRC it's found a handful of issues before so I'm not 
sure it's sane to just toss it.

I've put this all on the riscv-pgtable_static_key branch of 
kernel.org/palmer/linux .  If nobody has the time to look then I'll try 
and give it another shot, but I'm pretty buried right now so happy to 
have the help.

>
>>
>>  arch/riscv/include/asm/pgalloc.h    | 16 ++++----
>>  arch/riscv/include/asm/pgtable-32.h |  3 ++
>>  arch/riscv/include/asm/pgtable-64.h | 60 ++++++++++++++++++---------
>>  arch/riscv/include/asm/pgtable.h    |  5 +--
>>  arch/riscv/kernel/cpu.c             |  4 +-
>>  arch/riscv/kernel/setup.c           |  2 +-
>>  arch/riscv/mm/init.c                | 64 ++++++++++++++++++-----------
>>  arch/riscv/mm/kasan_init.c          | 16 ++++----
>>  8 files changed, 104 insertions(+), 66 deletions(-)
>>
>> --
>> 2.34.1
>>