linux-kernel - Re: [PATCH v4 0/2] use static key to optimize pgtable_l4

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Date:   Fri, 15 Jul 2022 21:35:43 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     anup@...infault.org, 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,
        Atish Patra <atishp@...osinc.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH v4 0/2] use static key to optimize pgtable_l4_enabled

On Fri, Jul 01, 2022 at 08:48:25PM -0700, Palmer Dabbelt wrote:
> On Sat, 25 Jun 2022 21:33:07 PDT (-0700), anup@...infault.org wrote:
> > On Sat, May 21, 2022 at 8:13 PM Jisheng Zhang <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 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@...infault.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

Hi Palmer,

Thank you for the hint, I find the reason: SPARSEMEM is the key, KASAN
doesn't matter. To fix this issue, we need to move
riscv_finalise_pgtable_lx() after sparse_init(). I will send out a
newer version soon.

> 
> 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.

Let me know if you want a seperate patch against
riscv-pgtable_static_key branch.

Thanks

> 
> > 
> > > 
> > >  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
> > >