linux-kernel - Re: [PATCH v3 07/17] dma-mapping: Implement link/unlink ranges API

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Message-ID: <20241119173004.GA773835@ziepe.ca>
Date: Tue, 19 Nov 2024 13:30:04 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Leon Romanovsky <leon@...nel.org>
Cc: Will Deacon <will@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
	Keith Busch <kbusch@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 07/17] dma-mapping: Implement link/unlink ranges API

On Tue, Nov 19, 2024 at 03:57:43PM +0200, Leon Romanovsky wrote:

> > > dma_iova_link/dma_iova_unlink() don't have any assumptions in addition
> > > to already existing for dma_map_sg/dma_unmap_sg(). In reality, it means
> > > that all calls to unlink will have same size as for link.
> > 
> > Ok, great. Any chance you could call that out in the documentation patch,
> > please?
> 
> Can you suggest what should I add there, as it is not specific to new
> API, but general note applicable to all __iommu_unmap() callers?

This is what I wrote:

+/**
+ * iommu_unmap() - Remove mappings from a range of IOVA
+ * @domain: Domain to manipulate
+ * @iova: IO virtual address to start
+ * @size: Length of the range starting from @iova
+ *
+ * iommu_unmap() will remove a translation created by iommu_map(). It cannot
+ * subdivide a mapping created by iommu_map(), so it should be called with IOVA
+ * ranges that match what was passed to iommu_map(). The range can aggregate
+ * contiguous iommu_map() calls so long as no individual range is split.
+ *
+ * Returns: Number of bytes of IOVA unmapped. iova + res will be the point
+ * unmapping stopped.
+ */

Jason