Re: [RFC PATCH 08/11] x86,fpu: restore user FPU state lazily after __kernel_fpu_end

Oleg Nesterov
2015-01-14T18:44:45Z

On 01/11, riel@redhat.com wrote:
>
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -89,13 +89,11 @@ void __kernel_fpu_end(void)
> if (use_eager_fpu()) {
> /*
> * For eager fpu, most the time, tsk_used_math() is true.
> - * Restore the user math as we are done with the kernel usage.
> - * At few instances during thread exit, signal handling etc,
> - * tsk_used_math() is false. Those few places will take proper
> - * actions, so we don't need to restore the math here.
> + * Make sure the user math state is restored on return to
> + * userspace.
> */
> if (likely(tsk_used_math(current)))
> - math_state_restore();
> + set_thread_flag(TIF_LOAD_FPU);

Hmm. And this looks obviously wrong if interrupted_user_mode().

Oleg.