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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Dave Hansen <dave.hansen@intel.com>,
        "H.J. Lu" <hjl.tools@gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andi Kleen <ak@linux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Linux-MM <linux-mm@kvack.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFCv2 00/10] Linear Address Masking enabling
In-Reply-To: <ee786113-2173-b78b-774d-9d61d08b069b@intel.com>
References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com>
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 <87o802tjd7.ffs@tglx>
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 <67aef839-0757-37b1-a42d-154c0116cbf5@intel.com> <878rr6te6b.ffs@tglx>
 <ee786113-2173-b78b-774d-9d61d08b069b@intel.com>
Date:   Fri, 13 May 2022 10:28:31 +0200
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On Thu, May 12 2022 at 20:05, Dave Hansen wrote:

> On 5/12/22 18:27, Thomas Gleixner wrote:
>> On Thu, May 12 2022 at 17:46, Dave Hansen wrote:
>>> On 5/12/22 17:08, H.J. Lu wrote:
>>> If I had to take a shot at this today, I think I'd opt for:
>>>
>>> 	mask = sys_enable_masking(bits=6, flags=FUZZY_NR_BITS);
>>>
>>> although I'm not super confident about the "fuzzy" flag.  I also don't
>>> think I'd totally hate the "blind" interface where the kernel just gets
>>> to pick unilaterally and takes zero input from userspace.
>> That's the only sane choice and you can make it simple for userspace:
>> 
>>        ret = prctl(GET_XXX_MASK, &mask);
>> 
>> and then let it decide based on @ret and @mask whether to use it or not.
>> 
>> But of course nobody thought about this as a generic feature and so we
>> have the ARM64 TBI muck as a precedence.
>
> Well, not quite *nobody*:
>
>  https://lore.kernel.org/linux-arm-kernel/7a34470c-73f0-26ac-e63d-161191d4b1e4@intel.com/

Sigh....