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

[Jessica Clarke]

On 11 Jan 2023, at 19:00, Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
> On Thu, Jan 12, 2023 at 01:28:40AM +0800, Jisheng Zhang wrote:
>> On Sun, Dec 11, 2022 at 06:44:04PM +0800, Jisheng Zhang wrote:
>>> On Sat, Oct 08, 2022 at 10:28:35PM +0800, Jisheng Zhang wrote:
>>>> 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@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.
>>>> 
>>>> 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
>>> 
>>> Hi Palmer,
>>> 
>>> I think the early boot hangs maybe the same as the one which has been
>>> fixed by commit 9f2ac64d6ca6 ("riscv: mm: add missing memcpy in
>>> kasan_init"). Will you give this series another try for v6.2-rc1? If
>>> the boot hang can still be reproduced, could you please send me your
>>> .config file?
>>> 
>>> Thanks in advance
>> Hi all,
>> 
>> Just request to comment what to do with this patch, I think there
>> are two independent points to consult:
>> 
>> 1. IIRC, Palmer gave this patch two chances to merge in early versions
>> but he found boot hangs if enable KASAN and SPARSEMEM, while I can't
>> reproduce the boot hang. And I also expect the hang should be fixed by
>> commit 9f2ac64d6ca6 ("riscv: mm: add missing memcpy in kasan_init")
>> 
>> 2. Now we know alternative is preferred than static branch for ISA
>> extensions dynamic code patching. So we also need to switch static
>> branch usage here to alternative mechanism, but the problem is
>> SV48 and SV57 are not ISA extensions, so we can't directly make use
>> of the recently introduced riscv_has_extension_likely|unlikely()[1] 
>> which is based on alternative mechanism.
> 
> We could rename the "has_extension" framework to "has_cpufeature" and
> then lump extensions and features such as sv48 and sv57 together. Or,
> if it's best to keep extensions separate, then duplicate the framework
> to create a "has_non_extension_feature" version where features like
> sv48 and sv57 live.

Sv39, Sv48 and Sv57 are extensions these days (see the draft profiles
spec[1] and [2]).

Jess

[1] https://github.com/riscv/riscv-profiles/blob/main/profiles.adoc#522-rva20s64-mandatory-extensions
[2] https://wiki.riscv.org/display/HOME/Recently+Ratified+Extensions

> Thanks,
> drew
> 
>> 
>> Any comments are appreciated.
>> 
>> Thanks in advance
>> 
>> [1] https://lore.kernel.org/linux-riscv/20230111171027.2392-1-jszhang@xxxxxxxxxx/T/#t
>> 
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