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

[Alex Bennée <alex.bennee@xxxxxxxxxx>]

Dave Martin <Dave.Martin@xxxxxxx> 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@xxxxxxx>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>

> ---
>  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