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

[Ard Biesheuvel]

On Tue, 21 May 2024 at 08:22, Johannes Nixdorf <mixi at shadowice.org> wrote:
>
> Bad news: I hit the bug again with 2632e2521769 ("arm64: fpsimd: Implement
> lazy restore for kernel mode FPSIMD") reverted during prolonged interactive
> usage with the downstream Asahi Linux kernel.
>
> This prompted me to adjust the reproducer to be closer to the desktop use
> case, which then also found aefbab8e77eb ("arm64: fpsimd: Preserve/restore
> kernel mode NEON at context switch"). With the vanilla kernel before the
> commit or that commit reverted on the Asahi Linux kernel the new reproducer
> also sees no bug, and interactive usage seems fine.
>
> The old reproducer used a loop device backed by the initramfs' tmpfs. The
> new reproducer now uses the actual hardware nvme device as backend:
>
> init:
>  dev=/dev/nvme0n1p7
>  dm_name=test
>  dm_dev=/dev/mapper/${dm_name}
>  echo test | cryptsetup luksFormat -q ${dev}
>  echo test | cryptsetup open ${dev} test
>  mkfs.ext4 ${dm_dev}
>  mount ${dm_dev} /target
>  cd /target
>  fio /verify.fio
>
> verify.fio:
>  [write-and-verify]
>  loops=10
>  rw=randwrite
>  bs=4k
>  direct=1
>  ioengine=libaio
>  iodepth=16
>  verify=crc32c
>  size=1G
>

Thanks for these instructions - I am trying to reproduce but no 'luck' yet.

Could you please share your complete kernel config (based on the
vanilla kernel at commit aefbab8e77eb), and a dump of the FIO output
on a failure case?