linux-kernel - Re: [PATCH v6 RESEND 0/2] use static key to optimize pgtable_l4

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Date:   Sat, 8 Oct 2022 22:28:30 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        ryabinin.a.a@...il.com, glider@...gle.com, andreyknvl@...il.com,
        dvyukov@...gle.com, vincenzo.frascino@....com,
        alexandre.ghiti@...onical.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v6 RESEND 0/2] use static key to optimize
 pgtable_l4_enabled

On Thu, Oct 06, 2022 at 04:37:57PM +0800, Jisheng Zhang wrote:
> On Wed, Oct 05, 2022 at 06:05:28PM -0700, Palmer Dabbelt wrote:
> > On Sun, 21 Aug 2022 07:09:16 PDT (-0700), jszhang@...nel.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 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.

Hi Palmer,

I know you are busy ;) Do you have time to send me your test kernel
config file so that I can reproduce the "early boot hang"?

Thanks