Re: [PATCH v2 17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use

[Alex Bennée]

Dave Martin <dave.mar...@arm.com> writes:

> Kernel-mode NEON will corrupt the SVE vector registers, due to the
> way they alias the FPSIMD vector registers in the hardware.
>
> This patch ensures that any live SVE register content for the task
> is saved by kernel_neon_begin().  The data will be restored in the
> usual way on return to userspace.
>
> Signed-off-by: Dave Martin <dave.mar...@arm.com>
> Reviewed-by: Ard Biesheuvel <ard.biesheu...@linaro.org>

Reviewed-by: Alex Bennée <alex.ben...@linaro.org>

> ---
>  arch/arm64/kernel/fpsimd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index cea05a7..dd89acf 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -744,8 +744,10 @@ void kernel_neon_begin(void)
>       __this_cpu_write(kernel_neon_busy, true);
>
>       /* Save unsaved task fpsimd state, if any: */
> -     if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
> -             fpsimd_save_state(&current->thread.fpsimd_state);
> +     if (current->mm) {
> +             task_fpsimd_save();
> +             set_thread_flag(TIF_FOREIGN_FPSTATE);
> +     }
>
>       /* Invalidate any task state remaining in the fpsimd regs: */
>       __this_cpu_write(fpsimd_last_state, NULL);


--
Alex Bennée
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