Re: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get_user()

[Al Viro]

On Sun, Mar 29, 2020 at 10:56:59AM -0700, Linus Torvalds wrote:

> But, if you have lots of performance-critical get_user() calls, just use
> 
>      if (user_access_begin(..))
>         goto efault;
> 
>      .. multiple "unsafe_get_user(x,ptr,efault);" ..
> 
>      user_access_end();
>      ...
> 
>   efault:
>      user_access_end();
>      return -EFAULT;
> 
> and be done with it.

Except that you'd better make that
	if (!user_access_begin(...))
		return -EFAULT;