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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Dmitry Vyukov <dvyukov@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        Alexander Potapenko <glider@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 00/10] Linear Address Masking enabling
In-Reply-To: <878rr6v985.ffs@tglx>
References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com>
 <20220511064943.GR76023@worktop.programming.kicks-ass.net>
 <87pmkivjst.ffs@tglx> <20220512165612.gizedzgtpzbi7jbl@black.fi.intel.com>
 <878rr6v985.ffs@tglx>
Date:   Fri, 13 May 2022 01:21:37 +0200
Message-ID: <87r14ytjzy.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Thu, May 12 2022 at 21:31, Thomas Gleixner wrote:
> On Thu, May 12 2022 at 19:56, Kirill A. Shutemov wrote:
>> On Thu, May 12, 2022 at 05:42:58PM +0200, Thomas Gleixner wrote:
>>> On Wed, May 11 2022 at 08:49, Peter Zijlstra wrote:
>>> > On Wed, May 11, 2022 at 05:27:40AM +0300, Kirill A. Shutemov wrote:
>>> > So aren't we creating a problem with LAM_U48 where programs relying on
>>> > it are of limited sustainability?
>>> >
>>> > Any such program simply *cannot* run on 5 level pagetables. Why do we
>>> > want to do this?
>>> 
>>> More bits are better :)
>>> 
>>> Seriously, I agree that restricting it to LAM57, which gives us 6 bits,
>>> makes a lot of sense _and_ makes the whole thing way simpler.
>>> 
>>> So supporting both needs a truly good justification and a real world use
>>> case.
>>
>> I asked the question before[1]. Basically, more bits more better:
>>
>> 	For HWASAN #bits == detection probability.
>> 	For MarkUS #bits == exponential cost reduction
>
> What is MarkUS? It's not really helpful to provide acronyms which are
> not decodable.
>
>> I would really like to have only LAM_U57, but IIUC 6 bits is not always
>> enough.
>>
>> Dmitry, could you elaborate?
>>
>> [1] https://mobile.twitter.com/dvyukov/status/1342019823400837120
>
> I don't know whether he reacts on posting a link to his twitter
> account. I've CC'ed him now. Maybe that works better.

Duh. I should have looked at 'To:' and not only at 'Cc:'

Maybe someday I get used to this email thing.

Thanks,

        tglx