Re: [PATCH 18/24] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD

[Sebastian Andrzej Siewior]

On 2019-03-31 20:20:25 [+0200], Thomas Gleixner wrote:
> 
> I think this should do the following:
> 
> 	fpregs_lock();
> 	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
> 		pagefault_disable();
> 		ret = copy_fpu_to_user(...);
> 		pagefault_enable();
> 		if (!res)
> 			return 0;
> 		copy_fpregs_to_fpstate(fpu); 
> 	}
> 	fpregs_unlock();
> 
> The point is that in most cases the direct store from the FPU registers to
> user space will succeed simply because the stack is accessible and you only
> do the store in kernel memory and copy when that fails.

let me try that.

> Thanks,
> 
> 	tglx
> 

Sebastian