Re: [PATCH Dovetail] arm64: fpsimd: dovetail: Allow preemption of in-band fpsimd kernel sections

[Philippe Gerum <rpm@xenomai.org>]

Florian Bezdeka <florian.bezdeka@siemens.com> writes:

> Preemption of in-band in-kernel fpsimd sections was not allowed /
> properly implemented in Dovetail up to now.
>
> That piled up again as some crypto code was optimized for arm64 in
> Linux 6.14. A possible call stack that makes clear that the FPU was
> corrupted follows. The inband stage was using crypto/FPU code inside
> the kernel and got interrupted by OOB.
>
> 	[  331.703695]  task_fpsimd_load+0xd0/0x214 (P)
> 	[  331.703713]  fpsimd_restore_current_state+0x9c/0xb8
> 	[  331.703732]  fpsimd_restore_current_oob+0x1c/0x2c
> 	[  331.703751]  dovetail_context_switch+0x90/0x180
> 	[  331.703769]  pipeline_switch_to+0x10/0x1c
> 	[  331.703792]  ___xnsched_run+0x1bc/0x29c
> 	[  331.703811]  run_oob_call+0x98/0x17c
> 	[  331.703830]  handle_irq_pipelined_finish+0x1e0/0x1ec
> 	[  331.703848]  handle_irq_pipelined+0x58/0x6c
> 	[  331.703865]  call_on_irq_stack+0x24/0x4c
> 	[  331.703884]  do_interrupt_handler+0x150/0x178
> 	[  331.703902]  el1_interrupt+0x44/0x11c
> 	[  331.703921]  el1h_64_irq_handler+0x18/0x24
> 	[  331.703941]  el1h_64_irq+0x6c/0x70                <- oob
> 	[  331.703957]  crc32c_le_arm64_4way+0x4c/0xc0 (P)   <- inband
> 	[  331.703978]  ext4_block_bitmap_csum_set+0x38/0x60
> 	[  331.704002]  ext4_mb_mark_context+0x1b0/0x398
> 	[  331.704025]  ext4_mb_mark_diskspace_used+0xd8/0x1f8
>
> To fix that we have to hook into the task switch as we do on x86 and
> invoke the FPU (re)store logic.
>
> Cc: powertree <powertree@163.com>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> Cc: Philippe Gerum <rpm@xenomai.org>
>
> Signed-off-by: Florian Bezdeka <florian.bezdeka@siemens.com>
> ---
>  arch/arm64/include/asm/dovetail.h    | 10 +++++++--
>  arch/arm64/include/asm/fpsimd.h      |  7 +++++-
>  arch/arm64/include/asm/thread_info.h |  1 +
>  arch/arm64/kernel/fpsimd.c           | 33 ++++++++++++++++++++++++++++
>  4 files changed, 48 insertions(+), 3 deletions(-)

LGTM, stable under significant stress load on imx8mp.

    Acked-by: Philippe Gerum <rpm@xenomai.org>

-- 
Philippe.