From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F35F6C11D3D for ; Thu, 27 Feb 2020 17:55:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C49532469B for ; Thu, 27 Feb 2020 17:55:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C49532469B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=deltatee.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 631626B0005; Thu, 27 Feb 2020 12:55:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 5E2216B0006; Thu, 27 Feb 2020 12:55:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4F84B6B0007; Thu, 27 Feb 2020 12:55:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0154.hostedemail.com [216.40.44.154]) by kanga.kvack.org (Postfix) with ESMTP id 3A2276B0005 for ; Thu, 27 Feb 2020 12:55:03 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 0BFA252B8 for ; Thu, 27 Feb 2020 17:55:03 +0000 (UTC) X-FDA: 76536658086.14.basin65_ef341cdad115 X-HE-Tag: basin65_ef341cdad115 X-Filterd-Recvd-Size: 3802 Received: from ale.deltatee.com (ale.deltatee.com [207.54.116.67]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Thu, 27 Feb 2020 17:55:02 +0000 (UTC) Received: from s0106ac1f6bb1ecac.cg.shawcable.net ([70.73.163.230] helo=[192.168.11.155]) by ale.deltatee.com with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1j7NMx-0004I6-PN; Thu, 27 Feb 2020 10:54:45 -0700 To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-mm@kvack.org, Dan Williams , Michal Hocko , David Hildenbrand , Andrew Morton , Christoph Hellwig , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Eric Badger References: <20200221182503.28317-1-logang@deltatee.com> <20200227171704.GK31668@ziepe.ca> <20200227174311.GL31668@ziepe.ca> From: Logan Gunthorpe Message-ID: <7e573498-81c1-7f00-c1ff-ed16e12a5b96@deltatee.com> Date: Thu, 27 Feb 2020 10:54:40 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200227174311.GL31668@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 70.73.163.230 X-SA-Exim-Rcpt-To: ebadger@gigaio.com, peterz@infradead.org, luto@kernel.org, dave.hansen@linux.intel.com, bp@alien8.de, mingo@redhat.com, tglx@linutronix.de, benh@kernel.crashing.org, will@kernel.org, catalin.marinas@arm.com, hch@lst.de, akpm@linux-foundation.org, david@redhat.com, mhocko@kernel.org, dan.j.williams@intel.com, linux-mm@kvack.org, platform-driver-x86@vger.kernel.org, linux-sh@vger.kernel.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v3 0/7] Allow setting caching mode in arch_add_memory() for P2PDMA X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2020-02-27 10:43 a.m., Jason Gunthorpe wrote: > Hm, AFAIK WC memory is not compatible with the spinlocks/mutexs/etc in > Linux, so while it is true the memory has no side effects, there would > be surprising concurrency risks if anything in the kernel tried to > write to it. > > Not compatible means the locks don't contain stores to WC memory the > way you would expect. AFAIK on many CPUs extra barriers are required > to keep WC stores ordered, the same way ARM already has extra barriers > to keep UC stores ordered with locking.. > > The spinlocks are defined to contain UC stores though. > > If there is no actual need today for WC I would suggest using UC as > the default. Ok, that sounds sensible. I'll do that in the next revision. Thanks, Logan