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

  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.Martin@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm64/kernel/fpsimd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
  

Dave Martin <Dave.Martin@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.Martin@arm.com>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@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