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 A5923C4360C for ; Fri, 27 Sep 2019 21:21:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7CD2D205F4 for ; Fri, 27 Sep 2019 21:21:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728033AbfI0VVI (ORCPT ); Fri, 27 Sep 2019 17:21:08 -0400 Received: from verein.lst.de ([213.95.11.211]:47777 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725306AbfI0VVI (ORCPT ); Fri, 27 Sep 2019 17:21:08 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 569A468B05; Fri, 27 Sep 2019 23:21:04 +0200 (CEST) Date: Fri, 27 Sep 2019 23:21:04 +0200 From: Christoph Hellwig To: Halil Pasic Cc: Robin Murphy , Christoph Hellwig , linux-s390@vger.kernel.org, Janosch Frank , Vasily Gorbik , Cornelia Huck , Heiko Carstens , Peter Oberparleiter , linux-kernel@vger.kernel.org, Christian Borntraeger , iommu@lists.linux-foundation.org, Gerald Schaefer Subject: Re: [RFC PATCH 1/3] dma-mapping: make overriding GFP_* flags arch customizable Message-ID: <20190927212104.GC16819@lst.de> References: <20190923123418.22695-1-pasic@linux.ibm.com> <20190923123418.22695-2-pasic@linux.ibm.com> <20190923152117.GA2767@lst.de> <20190926143745.68bdd082.pasic@linux.ibm.com> <6c62da57-c94c-8078-957c-b6832ed7fd1b@arm.com> <20190927023314.3e5c8324.pasic@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190927023314.3e5c8324.pasic@linux.ibm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 27, 2019 at 02:33:14AM +0200, Halil Pasic wrote: > Thank you for your feedback. Just to be sure we are on the same pager, I > read commit a0be1db4304f like this: > 1) virtio_pci_legacy needs to allocate the virtqueues so that the base > address fits 44 bits > 2) if 64 bit dma is possible they set coherent_dma_mask to > DMA_BIT_MASK(44) and dma_mask to DMA_BIT_MASK(64) > 3) since the queues get allocated with coherent allocations 1) is > satisfied > 4) when the streaming mappings see a buffer that is beyond > DMA_BIT_MASK(44) then it has to treat it as not coherent memory > and do the syncing magic (which isn't actually required, just > a side effect of the workaround. 1-3 is correct, 4 is not. The coherent mask is a little misnamed and doesn't have to anything with coherency. It is the mask for DMA allocations, while the dma mask is for streaming mappings. > I've already implemented a patch (see after the scissors line) that > takes a similar route as commit a0be1db4304f, but I consider that a > workaround at best. But if that is what the community wants... I have to > get the job done one way or the other. That patch (minus the comments about being a workaround) is what you should have done from the beginning.