linux-kernel - Re: [PATCH 2/2] powerpc/64s: Trim offlined CPUs from mm

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Message-ID: <CAMuHMdUdorW03=mipgm92SXNPBZO5owW1Wp6_SacRDZ7fOe9gw@mail.gmail.com>
Date:   Thu, 10 Dec 2020 10:06:50 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anton Vorontsov <anton.vorontsov@...aro.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] powerpc/64s: Trim offlined CPUs from mm_cpumasks

Hi Nicholas,

On Fri, Nov 20, 2020 at 4:01 AM Nicholas Piggin <npiggin@...il.com> wrote:
>
> When offlining a CPU, powerpc/64s does not flush TLBs, rather it just
> leaves the CPU set in mm_cpumasks, so it continues to receive TLBIEs
> to manage its TLBs.
>
> However the exit_flush_lazy_tlbs() function expects that after
> returning, all CPUs (except self) have flushed TLBs for that mm, in
> which case TLBIEL can be used for this flush. This breaks for offline
> CPUs because they don't get the IPI to flush their TLB. This can lead
> to stale translations.
>
> Fix this by clearing the CPU from mm_cpumasks, then flushing all TLBs
> before going offline.
>
> These offlined CPU bits stuck in the cpumask also prevents the cpumask
> from being trimmed back to local mode, which means continual broadcast
> IPIs or TLBIEs are needed for TLB flushing. This patch prevents that
> situation too.
>
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>

Thanks for your patch!

> --- a/arch/powerpc/platforms/powermac/smp.c
> +++ b/arch/powerpc/platforms/powermac/smp.c
> @@ -911,6 +911,8 @@ static int smp_core99_cpu_disable(void)
>
>         mpic_cpu_set_priority(0xf);
>
> +       cleanup_cpu_mmu_context();
> +

I guess this change broke pmac32_defconfig+SMP in v5.10-rc7?

arch/powerpc/platforms/powermac/smp.c: error: implicit
declaration of function 'cleanup_cpu_mmu_context'
[-Werror=implicit-function-declaration]:  => 914:2

http://kisskb.ellerman.id.au/kisskb/buildresult/14423174/


>         return 0;
>  }
>
> diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
> index 54c4ba45c7ce..cbb67813cd5d 100644
> --- a/arch/powerpc/platforms/powernv/smp.c
> +++ b/arch/powerpc/platforms/powernv/smp.c
> @@ -143,6 +143,9 @@ static int pnv_smp_cpu_disable(void)
>                 xive_smp_disable_cpu();
>         else
>                 xics_migrate_irqs_away();
> +
> +       cleanup_cpu_mmu_context();
> +
>         return 0;
>  }
>
> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> index f2837e33bf5d..a02012f1b04a 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> @@ -90,6 +90,9 @@ static int pseries_cpu_disable(void)
>                 xive_smp_disable_cpu();
>         else
>                 xics_migrate_irqs_away();
> +
> +       cleanup_cpu_mmu_context();
> +
>         return 0;
>  }
>
> --
> 2.23.0
>


--
Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds