Re: [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin()

[Dave Hansen]

On 6/22/20 11:33 AM, Andy Lutomirski wrote:
> Suppose you do:
> 
> double x = 1.0;
> 
> kernel_fpu_begin();
> 
> x += 2.0;
> 
> We want to make sure that GCC puts things in the right order.  I
> suppose that even a memory clobber is insufficient here, though.

Even with CONFIG_PREEMPT disabled, we still have:

	#define preempt_disable()                       barrier()

I don't see us supporting preemptible kernel_fpu regions any time soon,
so shouldn't this be sufficient now and for a long time?