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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 B9BFFC3F2D4 for ; Fri, 28 Feb 2020 15:04:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8BA16246A0 for ; Fri, 28 Feb 2020 15:04:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="QmD58Jr5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726796AbgB1PEi (ORCPT ); Fri, 28 Feb 2020 10:04:38 -0500 Received: from mail-wr1-f68.google.com ([209.85.221.68]:42527 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726805AbgB1PEi (ORCPT ); Fri, 28 Feb 2020 10:04:38 -0500 Received: by mail-wr1-f68.google.com with SMTP id p18so3275437wre.9 for ; Fri, 28 Feb 2020 07:04:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=2wX7TVsRPWlph7pT/yUYa9EScRJx6Bt/ZtuI3MJeqc0=; b=QmD58Jr5s6XBLi75aKomne6pIfi3eAwBW2uYAgqcgi9rYL6G2b64JBuAhhJ1f4te+t YMUkbgfFABgR0aUFU4JS096/XwdfBA48niRJ6aEs7tCqepHjgsV+l2E6wcg2Pjfx8yDo nf2skHBkoT9WNffr5CVK3OP/PqPaYbv3aLmg1bq6Ck4RCaCb9gSeMd1pwHi25t4XMDZ2 wTbnbrTrIL7bSS1pZZd4ftBNuWdi6gB3+KHzkO3i4r62kLW9iRm0F/3xPVeufpfeXlyV F/ABlN3x4IYUOzxYknE1CmZaru7JzdyANO9LsTAgaHuR2Jzumx6YW0C7y8C7WKLy44Wn wxpg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=2wX7TVsRPWlph7pT/yUYa9EScRJx6Bt/ZtuI3MJeqc0=; b=hDXXqUMN5W0DH1rMDGkZPzjbXR5tHrLInsSPX1AktPL8n5TmJgLWyZ2/Ms9JJVoaRG pChZ3FoWRXgvPxmt6NY14Df4wJfj9oIzV+7gkleDxtnKNQdADEeJAAnLKLR0SVh6ullh Po75FK2cSHb+C82lDCUmb8JyHfydahp0GtqfDoIAFhkSS62jrrHAj5LpG/mcGoYO3flT lMuJ/dKExlVMqojOkOUSE/KtXMLjY7aUr06mdH0uBgbo0Ctlj7fPK4Ni4rhh6fpcpEHV r3DfnALOHmFmLSaZc+DbpJGB2ZKJ49S3FXYo0wA8Y08TqYbznoOp9AgbrUG5x8N2CpTt iG/w== X-Gm-Message-State: APjAAAUdKTu/Q4fq1DVD0dDdfpHtCKD0UhnFTsHBNoPuPuXPyb3TXwGR oR8amyy5MENjSv0nO/xotwBH4w== X-Google-Smtp-Source: APXvYqy8YEE7PhfU6kfB6vVMG12QSn14jY2m/pgfxhc5df3Dfge/vtzS0lAN1v8FM3HtzCFu1cbkug== X-Received: by 2002:adf:b19d:: with SMTP id q29mr5140671wra.211.1582902275442; Fri, 28 Feb 2020 07:04:35 -0800 (PST) Received: from myrica ([2001:171b:c9a8:fbc0:116c:c27a:3e7f:5eaf]) by smtp.gmail.com with ESMTPSA id w19sm2377341wmc.22.2020.02.28.07.04.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Feb 2020 07:04:34 -0800 (PST) Date: Fri, 28 Feb 2020 16:04:27 +0100 From: Jean-Philippe Brucker To: Jason Gunthorpe Cc: mark.rutland@arm.com, linux-pci@vger.kernel.org, linux-mm@kvack.org, will@kernel.org, Dimitri Sivanich , catalin.marinas@arm.com, zhangfei.gao@linaro.org, devicetree@vger.kernel.org, kevin.tian@intel.com, Arnd Bergmann , robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org, Greg Kroah-Hartman , iommu@lists.linux-foundation.org, Andrew Morton , robin.murphy@arm.com, christian.koenig@amd.com Subject: Re: [PATCH v4 01/26] mm/mmu_notifiers: pass private data down to alloc_notifier() Message-ID: <20200228150427.GF2156@myrica> References: <20200224182401.353359-1-jean-philippe@linaro.org> <20200224182401.353359-2-jean-philippe@linaro.org> <20200224190056.GT31668@ziepe.ca> <20200225092439.GB375953@myrica> <20200225140814.GW31668@ziepe.ca> <20200228143935.GA2156@myrica> <20200228144844.GQ31668@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200228144844.GQ31668@ziepe.ca> Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Fri, Feb 28, 2020 at 10:48:44AM -0400, Jason Gunthorpe wrote: > On Fri, Feb 28, 2020 at 03:39:35PM +0100, Jean-Philippe Brucker wrote: > > > > + list_for_each_entry_rcu(bond, &io_mm->devices, mm_head) { > > > > + /* > > > > + * To ensure that we observe the initialization of io_mm fields > > > > + * by io_mm_finalize() before the registration of this bond to > > > > + * the list by io_mm_attach(), introduce an address dependency > > > > + * between bond and io_mm. It pairs with the smp_store_release() > > > > + * from list_add_rcu(). > > > > + */ > > > > + io_mm = rcu_dereference(bond->io_mm); > > > > > > A rcu_dereference isn't need here, just a normal derference is fine. > > > > bond->io_mm is annotated with __rcu (for iommu_sva_get_pasid_generic(), > > which does bond->io_mm under rcu_read_lock()) > > I'm surprised the bond->io_mm can change over the lifetime of the > bond memory.. The normal lifetime of the bond is between device driver calls to bind() and unbind(). If the mm exits early, though, we clear bond->io_mm. The bond is then stale but can only be freed when the device driver releases it with unbind(). > > > > > If io_mm->ctx and io_mm->ops are already valid before the > > > > mmu notifier is published, then we don't need that stuff. > > > > > > So, this trickyness with RCU is not a bad reason to introduce the priv > > > scheme, maybe explain it in the commit message? > > > > Ok, I've added this to the commit message: > > > > The IOMMU SVA module, which attaches an mm to multiple devices, > > exemplifies this situation. In essence it does: > > > > mmu_notifier_get() > > alloc_notifier() > > A = kzalloc() > > /* MMU notifier is published */ > > A->ctx = ctx; // (1) > > device->A = A; > > list_add_rcu(device, A->devices); // (2) > > > > The invalidate notifier, which may start running before A is fully > > initialized at (1), does the following: > > > > io_mm_invalidate(A) > > list_for_each_entry_rcu(device, A->devices) > > A = device->A; // (3) > > I would drop the work around from the decription, it is enough to say > that the line below needs to observe (1) after (2) and this is > trivially achieved by moving (1) to before publishing the notifier so > the core MM locking can be used. Ok, will do Thanks, Jean