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

Thomas Gleixner
2022-05-14T08:38:07Z

On Sat, May 14 2022 at 02:22, Kirill A. Shutemov wrote:

> 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()

Sure, but that makes this changelog not any more correct.