linux-kernel - Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED

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Date:   Thu, 16 Jun 2022 11:39:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.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: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and
 ARCH_ENABLE_TAGGED_ADDR

On Fri, Jun 10, 2022 at 05:35:25PM +0300, Kirill A. Shutemov wrote:
> Add a couple of arch_prctl() handles:
> 
>  - ARCH_ENABLE_TAGGED_ADDR enabled LAM. The argument is required number
>    of tag bits. It is rounded up to the nearest LAM mode that can
>    provide it. For now only LAM_U57 is supported, with 6 tag bits.

As stated in the reply to the other patch; this isn't a 'for now' thing.
Due to how the untag thing works. Supporting U48 on 5-level kernels is
going to require a more complicated untag.