linux-kernel - Re: [PATCH] arm64: neon: Fix function may_use

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Message-ID: <20180711125825.GM9486@e103592.cambridge.arm.com>
Date:   Wed, 11 Jul 2018 13:58:25 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     "Yandong.Zhao" <yandong77520@...il.com>, zhaoxb@...ndersoft.com,
        ard.biesheuvel@...aro.org, catalin.marinas@....com,
        linux-kernel@...r.kernel.org, zhaoyd@...ndersoft.com,
        linux-arm-kernel@...ts.infradead.org, fanlc0801@...ndersoft.com
Subject: Re: [PATCH] arm64: neon: Fix function may_use_simd() return error
 status

On Wed, Jul 11, 2018 at 01:05:19PM +0100, Will Deacon wrote:
> On Wed, Jul 11, 2018 at 07:06:28PM +0800, Yandong.Zhao wrote:
> > From: Yandong Zhao <yandong77520@...il.com>
> > 
> > It does not matter if the caller of may_use_simd() migrates to
> > another cpu after the call, but it is still important that the
> > kernel_neon_busy percpu instance that is read matches the cpu the
> > task is running on at the time of the read.
> > 
> > This means that raw_cpu_read() is not sufficient.  kernel_neon_busy
> > may appear true if the caller migrates during the execution of
> > raw_cpu_read() and the next task to be scheduled in on the initial
> > cpu calls kernel_neon_begin().
> > 
> > This patch replaces raw_cpu_read() with this_cpu_read() to protect
> > against this race.
> > 
> > Fixes: cb84d11e1625 ("arm64: neon: Remove support for nested or hardirq kernel-mode NEON")
> > Reviewed-by: Dave Martin <Dave.Martin@....com>
> > Signed-off-by: Yandong Zhao <yandong77520@...il.com>
> > ---
> >  arch/arm64/include/asm/simd.h | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Does this need to go to stable?

It should, yes, so we should probably add

Cc: stable@...r.kernel.org


Are you OK to pick that up?

Cheers
---Dave