linux-kernel - Re: [PATCH RT] arm*: disable NEON in kernel mode

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Message-ID: <20171204092145.GE2255@linutronix.de>
Date:   Mon, 4 Dec 2017 10:21:46 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Dave Martin <Dave.Martin@....com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Mark Rutland <mark.rutland@....com>,
        linux-rt-users@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RT] arm*: disable NEON in kernel mode

On 2017-12-01 18:24:10 [+0000], Dave Martin wrote:
> > diff --git a/arch/arm64/crypto/Kconfig b/arch/arm64/crypto/Kconfig
> > index 70c517aa4501..2a5f05b5a19a 100644
> > --- a/arch/arm64/crypto/Kconfig
> > +++ b/arch/arm64/crypto/Kconfig
> > @@ -19,19 +19,19 @@ config CRYPTO_SHA512_ARM64
> >
> >  config CRYPTO_SHA1_ARM64_CE
> >     tristate "SHA-1 digest algorithm (ARMv8 Crypto Extensions)"
> > -   depends on KERNEL_MODE_NEON
> > +   depends on KERNEL_MODE_NEON && !PREEMPT_RT_BASE
> >     select CRYPTO_HASH
> >     select CRYPTO_SHA1
> 
> Sebastian, can you piont to where sha1 (say) hits this issue?
> I wonder whether this is really a sign that some refactoring is needed.

I disabled all NEON in one go. Looking at this, it shouldn't be a issue
with the block-walk. The only thing that might be a problem is that it
can do multiple blocks in one go.

> Cheers
> ---Dave

Sebastian