Re: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes

[Christian Brauner]

On Fri, Jun 12, 2020 at 11:38:33AM -0700, Kees Cook wrote:
> On Fri, Jun 12, 2020 at 08:28:16PM +0200, Christian Brauner wrote:
> > Al didn't want the PAGE_SIZE limit in there because there's nothing
> > inherently wrong with copying insane amounts of memory.
> 
> Right, ok.
> 
> > (Another tangent. I've asked this on Twitter not too long ago: do we
> > have stats how long copy_from_user()/copy_struct_from_user() takes with
> > growing struct/memory size? I'd be really interested in this. I have a
> > feeling that clone3()'s and - having had a chat with David Howells -
> > openat2()'s structs will continue to grow for a while... and I'd really
> > like to have some numbers on when copy_struct_from_user() becomes
> > costly or how costly it becomes.)
> 
> How long it takes? It should be basically the same, the costs should be
> mostly in switching memory protections, etc. I wouldn't imagine how many
> bytes being copied would matter much here, given the sub-page sizes.

This makes me _very_ happy.

Christian