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Tue, 28 Sep 2021 22:05:03 +0000 Received: from DM6PR12MB5520.namprd12.prod.outlook.com ([fe80::3817:44ce:52ad:3c0b]) by DM6PR12MB5520.namprd12.prod.outlook.com ([fe80::3817:44ce:52ad:3c0b%5]) with mapi id 15.20.4544.022; Tue, 28 Sep 2021 22:05:03 +0000 Date: Tue, 28 Sep 2021 19:05:02 -0300 From: Jason Gunthorpe To: Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Stephen Bates , Christoph Hellwig , Dan Williams , Christian =?utf-8?B?S8O2bmln?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy , Martin Oliveira , Chaitanya Kulkarni Subject: Re: [PATCH v3 4/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations Message-ID: <20210928220502.GA1738588@nvidia.com> References: <20210916234100.122368-1-logang@deltatee.com> <20210916234100.122368-5-logang@deltatee.com> Content-Type: text/plain; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=Pxlsptf+; spf=none (imf14.hostedemail.com: domain of jgg@nvidia.com has no SPF policy when checking 40.107.92.86) smtp.mailfrom=jgg@nvidia.com; dmarc=pass (policy=quarantine) header.from=nvidia.com X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 152846001983 X-Stat-Signature: yyw4wo6s3a9cj8gp9wm3mu8isg6r3ze8 X-HE-Tag: 1632866704-478000 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote: > +enum pci_p2pdma_map_type > +pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev, > + struct scatterlist *sg) > +{ > + if (state->pgmap != sg_page(sg)->pgmap) { > + state->pgmap = sg_page(sg)->pgmap; This has built into it an assumption that every page in the sg element has the same pgmap, but AFAIK nothing enforces this rule? There is no requirement that the HW has pfn gaps between the pgmaps linux decides to create over it. At least sg_alloc_append_table_from_pages() and probably something in the block world should be updated to not combine struct pages with different pgmaps, and this should be documented in scatterlist.* someplace. Jason