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Received: from s01060023bee90a7d.cg.shawcable.net ([24.64.145.4] helo=[192.168.0.10]) by ale.deltatee.com with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1knBLs-0005p7-VP; Wed, 09 Dec 2020 19:06:41 -0700 To: Dan Williams References: <20201106170036.18713-1-logang@deltatee.com> <20201106170036.18713-5-logang@deltatee.com> <20201109091258.GB28918@lst.de> <4e336c7e-207b-31fa-806e-c4e8028524a5@deltatee.com> From: Logan Gunthorpe Message-ID: Date: Wed, 9 Dec 2020 19:06:35 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-SA-Exim-Connect-IP: 24.64.145.4 X-SA-Exim-Rcpt-To: daniel.vetter@ffwll.ch, willy@infradead.org, ddutile@redhat.com, jhubbard@nvidia.com, iweiny@intel.com, christian.koenig@amd.com, jgg@ziepe.ca, sbates@raithlin.com, iommu@lists.linux-foundation.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, hch@lst.de, dan.j.williams@intel.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 04/15] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL 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) Cc: Jason Gunthorpe , Linux PCI , Daniel Vetter , Ira Weiny , Linux Kernel Mailing List , linux-nvme@lists.infradead.org, Stephen Bates , linux-block@vger.kernel.org, Linux MM , "open list:DMA MAPPING HELPERS" , Matthew Wilcox , John Hubbard , =?UTF-8?Q?Christian_K=c3=b6nig?= , Christoph Hellwig X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2020-12-09 6:22 p.m., Dan Williams wrote: > On Mon, Nov 9, 2020 at 8:47 AM Logan Gunthorpe wrote: >> >> >> >> On 2020-11-09 2:12 a.m., Christoph Hellwig wrote: >>> On Fri, Nov 06, 2020 at 10:00:25AM -0700, Logan Gunthorpe wrote: >>>> We make use of the top bit of the dma_length to indicate a P2PDMA >>>> segment. >>> >>> I don't think "we" can. There is nothing limiting the size of a SGL >>> segment. >> >> Yes, I expected this would be the unacceptable part. Any alternative ideas? > > Why is the SG_P2PDMA_FLAG needed as compared to checking the SGL > segment-pages for is_pci_p2pdma_page()? Because the DMA and page segments in the SGL aren't necessarily aligned... The IOMMU implementations can coalesce multiple pages into fewer DMA address ranges, so the page pointed to by sg->page_link may not be the one that corresponds to the address in sg->dma_address for a given segment. If that makes sense -- it's not the easiest thing to explain. Logan _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu