Re: [PATCH v6 RESEND 0/2] use static key to optimize pgtable_l4_enabled

[Jisheng Zhang]

On Wed, Oct 05, 2022 at 06:05:28PM -0700, Palmer Dabbelt wrote:
> On Sun, 21 Aug 2022 07:09:16 PDT (-0700), jszhang@xxxxxxxxxx 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@xxxxxxxxxx/T/#t
> > 
> > Since v5:
> >  - Use DECLARE_STATIC_KEY_FALSE
> > 
> > Since v4:
> >  - rebased on v5.19-rcN
> >  - collect Reviewed-by tags
> >  - Fix kernel panic issue if SPARSEMEM is enabled by moving the
> >    riscv_finalise_pgtable_lx() after sparse_init()
> > 
> > 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
> > 
> >  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(-)
> 
> Sorry for being slow here, but it looks like this still causes some early
> boot hangs.  Specifically kasan+sparsemem is failing.  As you can probably
> see from the latency I'm still a bit buried right now so I'm not sure when
> I'll have a chance to take more of a look.

Hi Palmer,

Before V4, there is a bug which can cause kernel panic when SPARSEMEM
is enabled, V4 have fixed it by moving the riscv_finalise_pgtable_lx()
after sparse_init(). And I just tested the riscv-pgtable_static_key
branch in your tree, enabling KASAN and SPARSEMEM, system booted fine.
I'm not sure what happened. Could you please send me your kernel
config file? I want to fix any issue which can block this series being
merged in 6.1-rc1.

Thanks in advance