Re: [RFCv2 08/10] x86/mm: Make LAM_U48 and mappings above 47-bits mutually exclusive

Kirill A. Shutemov
2022-05-13T23:32:04Z

On Thu, May 12, 2022 at 03:36:31PM +0200, Thomas Gleixner wrote:
> On Wed, May 11 2022 at 05:27, Kirill A. Shutemov wrote:
> > LAM_U48 steals bits above 47-bit for tags and makes it impossible for
> > userspace to use full address space on 5-level paging machine.
>
> > Make these features mutually exclusive: whichever gets enabled first
> > blocks the othe one.
>
> So this patch prevents a mapping above 47bit when LAM48 is enabled, but
> I fail to spot how an already existing mapping above 47bit would prevent
> LAM48 from being enabled.
>
> Maybe I'm missing something which makes this magically mutually
> exclusive.

It is in 09/10. See lam_u48_allowed()

--
Kirill A. Shutemov