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

[Ard Biesheuvel]

On Thu, 16 May 2024 at 18:25, Marc Zyngier <maz at 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.



> 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
> >
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>
> --
> Jazz is not dead. It just smells funny...