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b=CaAwoQJrZLArTEOfKusmY+hI3dr6PuiWIDAGemB23zwQ/bD7VJTzy3rb1U9K40ZyB /otipiTe+bwUNsaC6ZuVc/FviZm+4xAk2xQacK3lQNi9b9C6Rc7h/wCI7BS0VScrsf 4tpxSoBJ33RZtNcI49felKJ65GDyJxoFFc0vfS3DWE0TZBsc0CA7zajLlHMMZq2nJ1 BWwTxUhNOiJTR9T9zELEmujZkVJUUwVvWzO3p2r1Bum7+UJPdGxvl/n/B2MHdq+XCm MP6AVd9901F70GjDlGUnmWKECr+ExRRv6xOr2s0RZ4V/pVSadlxpSNJHRlLbIQ94pP b/fDR1hY0KIrA== Date: Thu, 4 Jul 2024 20:16:02 +0300 From: Leon Romanovsky To: Robin Murphy Cc: Jens Axboe , Jason Gunthorpe , Joerg Roedel , Will Deacon , Keith Busch , Christoph Hellwig , "Zeng, Oak" , Chaitanya Kulkarni , Sagi Grimberg , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , Marek Szyprowski , =?iso-8859-1?B?Suly9G1l?= Glisse , Andrew Morton , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v1 18/18] nvme-pci: use new dma API Message-ID: <20240704171602.GE95824@unreal> References: <47eb0510b0a6aa52d9f5665d75fa7093dd6af53f.1719909395.git.leon@kernel.org> <249ec228-4ffd-4121-bd51-f4a19275fee1@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <249ec228-4ffd-4121-bd51-f4a19275fee1@arm.com> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C9E20100004 X-Stat-Signature: 85j74myptnizwdf7ka7sci9gjhsxuowb X-HE-Tag: 1720113371-783756 X-HE-Meta: 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 JiivO5QZ djJOOivpql3Q1vulfw5uoLpaY0PAN5EE8UXohicLuhK1qkSyYfOKaDAbQMxDE4JV3uP9nF7DMgIdkM0P5Lowv7q2sMaC31Uox1/friO+XvllgcdedeznkXpQD87ou6hQ+aUE4Jep/iEyz+ey9+GleMGaMOcM/gnHLi2SuI4SoKnLUM3xuTFdlf3CAuIebEOyeYv+dJjGXSqM5FUQQcs+V/EhOjUdp58vFKvb/ 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: List-Subscribe: List-Unsubscribe: On Thu, Jul 04, 2024 at 04:23:47PM +0100, Robin Murphy wrote: > On 02/07/2024 10:09 am, Leon Romanovsky wrote: > [...] > > +static inline dma_addr_t nvme_dma_link_page(struct page *page, > > + unsigned int poffset, > > + unsigned int len, > > + struct nvme_iod *iod) > > { > > - int i; > > - struct scatterlist *sg; > > + struct dma_iova_attrs *iova = &iod->dma_map->iova; > > + struct dma_iova_state *state = &iod->dma_map->state; > > + dma_addr_t dma_addr; > > + int ret; > > + > > + if (iod->dma_map->use_iova) { > > + phys_addr_t phys = page_to_phys(page) + poffset; > > Yeah, there's no way this can possibly work. You can't do the > dev_use_swiotlb() check up-front based on some overall DMA operation size, > but then build that operation out of arbitrarily small fragments of > different physical pages that *could* individually need bouncing to not > break coherency. This is exactly how dma_map_sg() works. It checks in advance all SG and proceeds with bounce buffer if needed. In our case all checks which exists in dev_use_sg_swiotlb() will give "false". In v0, Christoph said that NVMe guarantees alignment, which is only one "dynamic" check in that function. 600 static bool dev_use_sg_swiotlb(struct device *dev, struct scatterlist *sg, 601 int nents, enum dma_data_direction dir) 602 { 603 struct scatterlist *s; 604 int i; 605 606 if (!IS_ENABLED(CONFIG_SWIOTLB)) 607 return false; 608 609 if (dev_is_untrusted(dev)) 610 return true; 611 612 /* 613 * If kmalloc() buffers are not DMA-safe for this device and 614 * direction, check the individual lengths in the sg list. If any 615 * element is deemed unsafe, use the swiotlb for bouncing. 616 */ 617 if (!dma_kmalloc_safe(dev, dir)) { 618 for_each_sg(sg, s, nents, i) 619 if (!dma_kmalloc_size_aligned(s->length)) 620 return true; 621 } 622 623 return false; 624 } ... 1338 static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, 1339 int nents, enum dma_data_direction dir, unsigned long attrs) ... 1360 if (dev_use_sg_swiotlb(dev, sg, nents, dir)) 1361 return iommu_dma_map_sg_swiotlb(dev, sg, nents, dir, attrs); Thanks > > Thanks, > Robin. > > > + > > + dma_addr = state->iova->addr + state->range_size; > > + ret = dma_link_range(&iod->dma_map->state, phys, len); > > + if (ret) > > + return DMA_MAPPING_ERROR; > > + } else { > > + dma_addr = dma_map_page_attrs(iova->dev, page, poffset, len, > > + iova->dir, iova->attrs); > > + } > > + return dma_addr; > > +} >