[RFC PATCH 1/1] riscv: mm: notify remote harts about mmu cache updates

[Lad, Prabhakar]

Hi Sergey,

On Thu, Dec 22, 2022 at 7:54 PM Sergey Matyukevich <geomatsi at gmail.com> wrote:
>
>
> Hi Prabhakar,
>
> > Hi Sergey,
> >
> > On Mon, Aug 29, 2022 at 9:53 PM Sergey Matyukevich <geomatsi at gmail.com> wrote:
> > >
> > > From: Sergey Matyukevich <sergey.matyukevich at syntacore.com>
> > >
> > > Current implementation of update_mmu_cache function performs local TLB
> > > flush. It does not take into account ASID information. Besides, it does
> > > not take into account other harts currently running the same mm context
> > > or possible migration of the running context to other harts. Meanwhile
> > > TLB flush is not performed for every context switch if ASID support
> > > is enabled.
> > >
> > > Patch [1] proposed to add ASID support to update_mmu_cache to avoid
> > > flushing local TLB entirely. This patch takes into account other
> > > harts currently running the same mm context as well as possible
> > > migration of this context to other harts.
> > >
> > > For this purpose the approach from flush_icache_mm is reused. Remote
> > > harts currently running the same mm context are informed via SBI calls
> > > that they need to flush their local TLBs. All the other harts are marked
> > > as needing a deferred TLB flush when this mm context runs on them.
> > >
> > > [1] https://lore.kernel.org/linux-riscv/20220821013926.8968-1-tjytimi@163.com/
> > >
> > > Signed-off-by: Sergey Matyukevich <sergey.matyukevich at syntacore.com>
> > > ---
> > >  arch/riscv/include/asm/mmu.h      |  2 ++
> > >  arch/riscv/include/asm/pgtable.h  |  2 +-
> > >  arch/riscv/include/asm/tlbflush.h | 18 ++++++++++++++++++
> > >  arch/riscv/mm/context.c           | 10 ++++++++++
> > >  arch/riscv/mm/tlbflush.c          | 28 +++++++++++-----------------
> > >  5 files changed, 42 insertions(+), 18 deletions(-)
> > >
<snip>
> > [  133.008752] Hardware name: Renesas SMARC EVK based on r9a07g043f01 (DT)
> > [  133.015338] Call Trace:
> > [  133.017778] [<ffffffff800055cc>] dump_backtrace+0x1c/0x24
> > [  133.023174] [<ffffffff80776836>] show_stack+0x2c/0x38
> > [  133.028214] [<ffffffff80780244>] dump_stack_lvl+0x3c/0x54
> > [  133.033597] [<ffffffff80780270>] dump_stack+0x14/0x1c
> > [  133.038633] [<ffffffff80776c00>] panic+0x102/0x29a
> > [  133.043409] [<ffffffff800137ba>] do_exit+0x704/0x70a
> > [  133.048362] [<ffffffff8001390e>] do_group_exit+0x24/0x70
> > [  133.053659] [<ffffffff8001de54>] get_signal+0x68a/0x6dc
> > [  133.058874] [<ffffffff8000494e>] do_work_pending+0xd6/0x44e
> > [  133.064427] [<ffffffff800036c2>] resume_userspace_slow+0x8/0xa
> > [  133.070249] ---[ end Kernel panic - not syncing: Attempted to kill
> > init! exitcode=0x0000000b ]---
> >
> > If I revert this patch [0] bonnie++ works as expected.
> >
> > Any pointers on what could be the issue here?
> >
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git/commit/?h=for-next&id=4bd1d80efb5af640f99157f39b50fb11326ce641
> >
> > Cheers,
> > Prabhakar
>
> Good catch. Thanks for reporting ! Discussion around the issue and
> possible ways to fix it can be found in the following email thread:
>
> https://lore.kernel.org/linux-riscv/20221111075902.798571-1-guoren@kernel.org/
>
> Could you please apply the patch from Guo Ren instead of [0] and check
> if you have any issues with your test ? Besides, could you please share
> your kernel configuration and the actual bonnie++ params from emmc_t_002.sh script ?
>
Thanks for the pointer, I'll undo my changes and test Guo's patch.

I have pasted the script here [0] and attached config.

[0] https://paste.debian.net/hidden/a7a769b5/


Cheers,
Prabhakar
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