Re: [BUG] dm-crypt broken after 2632e2521769 ("arm64: fpsimd: Implement lazy restore for kernel mode FPSIMD")

From: Mark Rutland <mark.rutland@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Johannes Nixdorf <mixi@shadowice.org>,
	Mark Brown <broonie@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [BUG] dm-crypt broken after 2632e2521769 ("arm64: fpsimd: Implement lazy restore for kernel mode FPSIMD")
Date: Fri, 17 May 2024 13:57:36 +0200	[thread overview]
Message-ID: <ZkdFgbqytrmrnnwx@J2N7QTR9R3> (raw)
In-Reply-To: <CAMj1kXELpd2aeDdywdNWvUu+guR2AR=Fwbgo6mpJxFht0Qyeuw@mail.gmail.com>

On Thu, May 16, 2024 at 07:17:00PM +0200, Ard Biesheuvel wrote:
> On Thu, 16 May 2024 at 18:25, Marc Zyngier <maz@kernel.org> wrote:
> >
> > + Ard, Broonie
> >
> 
> Ugh.
> 
> This is going to be tricky to track down if it takes 10G of data to reproduce.
> 
> For the time being, maybe we should just revert and take the time to
> really dig into this?
> 
> It appears to revert cleanly, and the performance gain of the
> optimization was never quantified in the first place, so perhaps we
> should get some numbers too when we bring it back.

I agree that reverting is the right thing to do.

The main functional reason we wanted this was in preparation for
PREEMPT_AUTO, and that's still a way off.

Mark.

> 
> 
> 
> > On 2024-05-16 17:22, Johannes Nixdorf wrote:
> > > I noticed frequent FS corruption on my M1 MacBook running Linux after
> > > the Asahi Linux Kernel was updated to 6.9.x (from 6.6.x).
> > >
> > > A git bisect pointed me to 2632e2521769 ("arm64: fpsimd: Implement lazy
> > > restore for kernel mode FPSIMD").
> > >
> > > This was reproduced with fio's examples/basic-verify.fio (1GB of
> > > writing
> > > was not reliably, 10GB triggered it reliably) on vanilla kernels and
> > > happens on any storage backend behind dm-crypt.
> > >
> > > I was advised to report it here on IRC.
> > >
> > > This was independently described in [1].
> > >
> > > Regards,
> > > Johannes Nixdorf
> > >
> > > [1]: https://github.com/tpwrules/nixos-apple-silicon/issues/200
> > >
> > > _______________________________________________
> > > linux-arm-kernel mailing list
> > > linux-arm-kernel@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
> > --
> > Jazz is not dead. It just smells funny...

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