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Message-ID: <87h75sse58.ffs@tglx>
Date: Sat, 14 May 2022 10:37:55 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
"H . J . Lu" <hjl.tools@...il.com>,
Andi Kleen <ak@...ux.intel.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFCv2 08/10] x86/mm: Make LAM_U48 and mappings above 47-bits
mutually exclusive
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.
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