linux-kernel - Re: [PATCH 0/3] sched, x86, arm64: PREEMPT

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Date:   Thu, 22 Jul 2021 15:11:05 -0500
From:   Andrew Halaney <ahalaney@...hat.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rt-users@...r.kernel.org, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Mark Brown <broonie@...nel.org>,
        Dave Martin <Dave.Martin@....com>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH 0/3] sched, x86, arm64: PREEMPT_RT, FPU and preemption

On Thu, Jul 22, 2021 at 06:51:54PM +0100, Valentin Schneider wrote:
> Hi folks,
> 
> This stems from some more v5.13-rt1 breakage on arm64. This time per-CPU access
> safety isn't sufficient, we really need to keep preemption disabled.
> 
> In a happy accident I stumbled on
> 
>   cba08c5dc6dc ("x86/fpu: Make kernel FPU protection RT friendly")
> 
> so I packaged what was done there into some common helpers and plastered them
> over the problematic areas.
> 
> Cheers,
> Valentin
> 
> Valentin Schneider (3):
>   sched/preempt: Introduce preempt_{enable, disable}_bh()
>   x86/fpu: Make FPU protection reuse common helper
>   arm64/fpsimd: Fix FPSIMD context handling vs PREEMPT_RT
> 
>  arch/arm64/kernel/fpsimd.c     |  6 ++++--
>  arch/x86/include/asm/fpu/api.h | 19 ++-----------------
>  include/linux/bottom_half.h    | 26 ++++++++++++++++++++++++++
>  3 files changed, 32 insertions(+), 19 deletions(-)
> 
> --
> 2.25.1
> 

I'm an outsider on all of this, but this series makes sense and looks
good to me.

Reviewed-by: Andrew Halaney <ahalaney@...hat.com>