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([2601:646:c200:7429:fdea:9bef:2d79:82f]) by smtp.gmail.com with ESMTPSA id m7-v6sm34221842pgq.59.2018.10.31.13.38.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Oct 2018 13:38:38 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 10/17] prmem: documentation From: Andy Lutomirski X-Mailer: iPhone Mail (16A404) In-Reply-To: <20181031101124.GO744@hirez.programming.kicks-ass.net> Date: Wed, 31 Oct 2018 13:38:37 -0700 Cc: Igor Stoppa , Matthew Wilcox , Tycho Andersen , Kees Cook , Mimi Zohar , Dave Chinner , James Morris , Michal Hocko , Kernel Hardening , linux-integrity , linux-security-module , Igor Stoppa , Dave Hansen , Jonathan Corbet , Laura Abbott , Randy Dunlap , Mike Rapoport , "open list:DOCUMENTATION" , LKML , Thomas Gleixner Content-Transfer-Encoding: quoted-printable Message-Id: <34204E6C-53C2-427D-A3B2-3D2E091D3E4B@amacapital.net> References: <40cd77ce-f234-3213-f3cb-0c3137c5e201@gmail.com> <20181030152641.GE8177@hirez.programming.kicks-ass.net> <0A7AFB50-9ADE-4E12-B541-EC7839223B65@amacapital.net> <20181030175814.GB10491@bombadil.infradead.org> <20181030182841.GE7343@cisco> <20181030192021.GC10491@bombadil.infradead.org> <9edbdf8b-b5fb-5a82-43b4-b639f5ec8484@gmail.com> <2cfb3835-0c18-b3fb-1722-5d693ae0ecd2@gmail.com> <20181031101124.GO744@hirez.programming.kicks-ass.net> To: Peter Zijlstra Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 31, 2018, at 3:11 AM, Peter Zijlstra wrote: >=20 >> On Wed, Oct 31, 2018 at 12:15:46AM +0200, Igor Stoppa wrote: >> On 30/10/2018 23:02, Andy Lutomirski wrote: >=20 >>> But I dislike allowing regular writes in the protected region. We >>> really only need four write primitives: >>>=20 >>> 1. Just write one value. Call at any time (except NMI). >>>=20 >>> 2. Just copy some bytes. Same as (1) but any number of bytes. >>>=20 >>> 3,4: Same as 1 and 2 but must be called inside a special rare write >>> region. This is purely an optimization. >>=20 >> Atomic? RCU? >=20 > RCU can be done, that's not really a problem. Atomics otoh are a > problem. Having pointers makes them just work. >=20 > Andy; I understand your reason for not wanting them, but I really don't > want to duplicate everything. Is there something we can do with static > analysis to make you more comfortable with the pointer thing? I=E2=80=99m sure we could do something with static analysis, but I think see= ing a real use case where all this fanciness makes sense would be good. And I don=E2=80=99t know if s390 *can* have an efficient implementation that= uses pointers. OTOH they have all kinds of magic stuff, so who knows?=