Re: [PATCH] x86: only use ERMS for user copies for larger sizes

[Linus Torvalds]

On Thu, Nov 22, 2018 at 9:36 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> The other problem with the ERMS copy is that it gets used
> for copy_to/from_io() - and the 'rep movsb' on uncached
> locations has to do byte copies.

Ugh. I thought we changed that *long* ago, because even our non-ERMS
copy is broken for PCI (it does overlapping stores for the small tail
cases).

But looking at "memcpy_{from,to}io()", I don't see x86 overriding it
with anything better.

I suspect nobody uses those functions for anything critical any more.
The fbcon people have their own copy functions, iirc.

But we definitely should fix this. *NONE* of the regular memcpy
functions actually work right for PCI space any more, and haven't for
a long time.

                 Linus