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=-5.3 required=3.0 tests=BAYES_00, 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 09036C433E0 for ; Sun, 7 Feb 2021 15:57:58 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5B11464DE1 for ; Sun, 7 Feb 2021 15:57:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5B11464DE1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4DYYhd3TvNzDrdp for ; Mon, 8 Feb 2021 02:57:53 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=lst.de (client-ip=213.95.11.211; helo=verein.lst.de; envelope-from=hch@lst.de; receiver=) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DYYfh12THzDvrL for ; Mon, 8 Feb 2021 02:56:10 +1100 (AEDT) Received: by verein.lst.de (Postfix, from userid 2407) id 3732F68B02; Sun, 7 Feb 2021 16:56:02 +0100 (CET) Date: Sun, 7 Feb 2021 16:56:01 +0100 From: Christoph Hellwig To: Dongli Zhang Subject: Re: [PATCH RFC v1 5/6] xen-swiotlb: convert variables to arrays Message-ID: <20210207155601.GA25111@lst.de> References: <20210203233709.19819-1-dongli.zhang@oracle.com> <20210203233709.19819-6-dongli.zhang@oracle.com> <20210204084023.GA32328@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210204084023.GA32328@lst.de> User-Agent: Mutt/1.5.17 (2007-11-01) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: ulf.hansson@linaro.org, airlied@linux.ie, joonas.lahtinen@linux.intel.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, bhelgaas@google.com, paulus@samba.org, hpa@zytor.com, hch@lst.de, m.szyprowski@samsung.com, sstabellini@kernel.org, adrian.hunter@intel.com, x86@kernel.org, joe.jin@oracle.com, mingo@kernel.org, peterz@infradead.org, mingo@redhat.com, bskeggs@redhat.com, linux-pci@vger.kernel.org, xen-devel@lists.xenproject.org, matthew.auld@intel.com, thomas.lendacky@amd.com, konrad.wilk@oracle.com, intel-gfx@lists.freedesktop.org, jani.nikula@linux.intel.com, bp@alien8.de, rodrigo.vivi@intel.com, nouveau@lists.freedesktop.org, boris.ostrovsky@oracle.com, chris@chris-wilson.co.uk, jgross@suse.com, tsbogend@alpha.franken.de, robin.murphy@arm.com, linux-mmc@vger.kernel.org, linux-mips@vger.kernel.org, iommu@lists.linux-foundation.org, tglx@linutronix.de, bauerman@linux.ibm.com, daniel@ffwll.ch, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, rppt@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Feb 04, 2021 at 09:40:23AM +0100, Christoph Hellwig wrote: > So one thing that has been on my mind for a while: I'd really like > to kill the separate dma ops in Xen swiotlb. If we compare xen-swiotlb > to swiotlb the main difference seems to be: > > - additional reasons to bounce I/O vs the plain DMA capable > - the possibility to do a hypercall on arm/arm64 > - an extra translation layer before doing the phys_to_dma and vice > versa > - an special memory allocator > > I wonder if inbetween a few jump labels or other no overhead enablement > options and possibly better use of the dma_range_map we could kill > off most of swiotlb-xen instead of maintaining all this code duplication? So I looked at this a bit more. For x86 with XENFEAT_auto_translated_physmap (how common is that?) pfn_to_gfn is a nop, so plain phys_to_dma/dma_to_phys do work as-is. xen_arch_need_swiotlb always returns true for x86, and range_straddles_page_boundary should never be true for the XENFEAT_auto_translated_physmap case. So as far as I can tell the mapping fast path for the XENFEAT_auto_translated_physmap can be trivially reused from swiotlb. That leaves us with the next more complicated case, x86 or fully cache coherent arm{,64} without XENFEAT_auto_translated_physmap. In that case we need to patch in a phys_to_dma/dma_to_phys that performs the MFN lookup, which could be done using alternatives or jump labels. I think if that is done right we should also be able to let that cover the foreign pages in is_xen_swiotlb_buffer/is_swiotlb_buffer, but in that worst case that would need another alternative / jump label. For non-coherent arm{,64} we'd also need to use alternatives or jump labels to for the cache maintainance ops, but that isn't a hard problem either.