[PATCH v2 2/4] arm64: fpsimd: Preserve/restore kernel mode NEON at context switch

[Eric Biggers]

On Thu, Nov 23, 2023 at 06:44:36PM +0100, Ard Biesheuvel wrote:
> -	/*
> -	 * Fix up TIF_FOREIGN_FPSTATE to correctly describe next's
> -	 * state.  For kernel threads, FPSIMD registers are never loaded
> -	 * and wrong_task and wrong_cpu will always be true.
> -	 */
> -	wrong_task = __this_cpu_read(fpsimd_last_state.st) !=
> -					&next->thread.uw.fpsimd_state;
> -	wrong_cpu = next->thread.fpsimd_cpu != smp_processor_id();
> +	if (test_tsk_thread_flag(next, TIF_USING_KMODE_FPSIMD)) {
> +		fpsimd_load_kernel_state(next);
> +		set_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE);
> +	} else {
> +		/*
> +		 * Fix up TIF_FOREIGN_FPSTATE to correctly describe next's
> +		 * state.  For kernel threads, FPSIMD registers are never
> +		 * loaded and wrong_task and wrong_cpu will always be true.
> +		 */
> +		wrong_task = __this_cpu_read(fpsimd_last_state.st) !=
> +			&next->thread.uw.fpsimd_state;
> +		wrong_cpu = next->thread.fpsimd_cpu != smp_processor_id();

The "For kernel threads, FPSIMD registers are never loaded" part is outdated
now, right?

- Eric