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 17D62C433DB for ; Sun, 7 Feb 2021 15:56:38 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 B6C9864DE8 for ; Sun, 7 Feb 2021 15:56:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6C9864DE8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.82424.152205 (Exim 4.92) (envelope-from ) id 1l8mPz-0002KY-Uj; Sun, 07 Feb 2021 15:56:11 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 82424.152205; Sun, 07 Feb 2021 15:56:11 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l8mPz-0002KR-Rd; Sun, 07 Feb 2021 15:56:11 +0000 Received: by outflank-mailman (input) for mailman id 82424; Sun, 07 Feb 2021 15:56:11 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l8mPz-0002KM-5n for xen-devel@lists.xenproject.org; Sun, 07 Feb 2021 15:56:11 +0000 Received: from verein.lst.de (unknown [213.95.11.211]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 3e0603dc-e1a6-405a-afa1-61ad820dc84d; Sun, 07 Feb 2021 15:56:08 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 3732F68B02; Sun, 7 Feb 2021 16:56:02 +0100 (CET) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 3e0603dc-e1a6-405a-afa1-61ad820dc84d Date: Sun, 7 Feb 2021 16:56:01 +0100 From: Christoph Hellwig To: Dongli Zhang Cc: dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux-foundation.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, nouveau@lists.freedesktop.org, x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, adrian.hunter@intel.com, akpm@linux-foundation.org, benh@kernel.crashing.org, bskeggs@redhat.com, bhelgaas@google.com, bp@alien8.de, boris.ostrovsky@oracle.com, hch@lst.de, chris@chris-wilson.co.uk, daniel@ffwll.ch, airlied@linux.ie, hpa@zytor.com, mingo@kernel.org, mingo@redhat.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, jgross@suse.com, konrad.wilk@oracle.com, m.szyprowski@samsung.com, matthew.auld@intel.com, mpe@ellerman.id.au, rppt@kernel.org, paulus@samba.org, peterz@infradead.org, robin.murphy@arm.com, rodrigo.vivi@intel.com, sstabellini@kernel.org, bauerman@linux.ibm.com, tsbogend@alpha.franken.de, tglx@linutronix.de, ulf.hansson@linaro.org, joe.jin@oracle.com, thomas.lendacky@amd.com 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) 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.