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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "H . J . Lu" <hjl.tools@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFCv2 08/10] x86/mm: Make LAM_U48 and mappings above 47-bits
 mutually exclusive
In-Reply-To: <20220513232242.7ac7herw7iyfkd2h@black.fi.intel.com>
References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com>
 <20220511022751.65540-10-kirill.shutemov@linux.intel.com>
 <875ymax480.ffs@tglx> <20220513232242.7ac7herw7iyfkd2h@black.fi.intel.com>
Date:   Sat, 14 May 2022 10:37:55 +0200
Message-ID: <87h75sse58.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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.