Re: [git pull] x86 PAT changes

Linus Torvalds
2008-04-26T01:13:20Z

On Fri, 25 Apr 2008, H. Peter Anvin wrote:
>
> The problem is that that can create cached/uncached aliases, which can cause
> some processors to lock up (especially AMD is known to have a lot of errata in
> this area.)

Umm.. I don't think you understand. Right now, NONPROMISC_DEVMEM doesn't
just disable mmap() on /dev/mem, it disables totally regular reads and
writes too. That seems pretty damn excessive.

If it was just mmap(), I don't think it would matter much. I don't think
we traditionally even supported mmap() on real RAM (because the page
counting would get confused), and that actually got supported only thanks
to VM changes that made it possible.

But read/write has always been supported, and shouldn't cause any
cached/uncached aliases!

Linus