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Tsirkin" , Miguel Ojeda , Robin Murphy , rust-for-linux@vger.kernel.org, Sagi Grimberg , Stefano Stabellini , Steven Rostedt , virtualization@lists.linux.dev, Will Deacon , xen-devel@lists.xenproject.org Subject: Re: [PATCH v6 00/16] dma-mapping: migrate to physical address-based API Message-ID: <20250912090327.GU341237@unreal> References: <0db9bce5-40df-4cf5-85ab-f032c67d5c71@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0db9bce5-40df-4cf5-85ab-f032c67d5c71@samsung.com> X-Rspamd-Queue-Id: 7C4AE10000B X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: wojj1jo9i7jabbbxr6uf1431emi7t49a X-HE-Tag: 1757915304-583981 X-HE-Meta: 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 s5I4jTD2 B7CiWg2rmAnIyvLrYpPg0HiTrWhGlAu+VYxnshEXWGtuQbVRv2X6CXE2GB5cZkBOGUjpwHRm9VWfS36Ya3n2SVJqI8qxy2a/Sew6U+DIhvaZDWAILmrbEUTRTpBIETvoB0fEFxCZ9tyevAcUSES3/crH33vZXLEfDMBslZ/VBJ/F0oXt1lhcZQgsTpN9cot4W+/r5FiHq51I4eBu3nwaJ1C4oZh/jmhLsa0GCpjwCyF5UPx8YlK+OnnXF0KGa+pQiiv+cHpvx2MFGm0rXLW9zz2zBQT4BqH5GtAoqNzHdwSTLwHesfYn4T6eGTCSWwiTeogmqOdUv3Zqx80mY+j6lXY+/jyKouzGMlCeu6YvKdjpVenEGatmKGInrwezq91kSSfpq8sg/2CTwtuXDDlscYZR01g== 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 Fri, Sep 12, 2025 at 12:25:38AM +0200, Marek Szyprowski wrote: > On 09.09.2025 15:27, Leon Romanovsky wrote: > > From: Leon Romanovsky > > > > Changelog: > > v6: > > * Based on "dma-debug: don't enforce dma mapping check on noncoherent > > allocations" patch. > > * Removed some unused variables from kmsan conversion. > > * Fixed missed ! in dma check. > > v5: https://lore.kernel.org/all/cover.1756822782.git.leon@kernel.org > > * Added Jason's and Keith's Reviewed-by tags > > * Fixed DMA_ATTR_MMIO check in dma_direct_map_phys > > * Jason's cleanup suggestions > > v4: https://lore.kernel.org/all/cover.1755624249.git.leon@kernel.org/ > > * Fixed kbuild error with mismatch in kmsan function declaration due to > > rebase error. > > v3: https://lore.kernel.org/all/cover.1755193625.git.leon@kernel.org > > * Fixed typo in "cacheable" word > > * Simplified kmsan patch a lot to be simple argument refactoring > > v2: https://lore.kernel.org/all/cover.1755153054.git.leon@kernel.org > > * Used commit messages and cover letter from Jason > > * Moved setting IOMMU_MMIO flag to dma_info_to_prot function > > * Micro-optimized the code > > * Rebased code on v6.17-rc1 > > v1: https://lore.kernel.org/all/cover.1754292567.git.leon@kernel.org > > * Added new DMA_ATTR_MMIO attribute to indicate > > PCI_P2PDMA_MAP_THRU_HOST_BRIDGE path. > > * Rewrote dma_map_* functions to use thus new attribute > > v0: https://lore.kernel.org/all/cover.1750854543.git.leon@kernel.org/ > > ------------------------------------------------------------------------ > > > > This series refactors the DMA mapping to use physical addresses > > as the primary interface instead of page+offset parameters. This > > change aligns the DMA API with the underlying hardware reality where > > DMA operations work with physical addresses, not page structures. > > > > The series maintains export symbol backward compatibility by keeping > > the old page-based API as wrapper functions around the new physical > > address-based implementations. > > > > This series refactors the DMA mapping API to provide a phys_addr_t > > based, and struct-page free, external API that can handle all the > > mapping cases we want in modern systems: > > > > - struct page based cacheable DRAM > > - struct page MEMORY_DEVICE_PCI_P2PDMA PCI peer to peer non-cacheable > > MMIO > > - struct page-less PCI peer to peer non-cacheable MMIO > > - struct page-less "resource" MMIO > > > > Overall this gets much closer to Matthew's long term wish for > > struct-pageless IO to cacheable DRAM. The remaining primary work would > > be in the mm side to allow kmap_local_pfn()/phys_to_virt() to work on > > phys_addr_t without a struct page. > > > > The general design is to remove struct page usage entirely from the > > DMA API inner layers. For flows that need to have a KVA for the > > physical address they can use kmap_local_pfn() or phys_to_virt(). This > > isolates the struct page requirements to MM code only. Long term all > > removals of struct page usage are supporting Matthew's memdesc > > project which seeks to substantially transform how struct page works. > > > > Instead make the DMA API internals work on phys_addr_t. Internally > > there are still dedicated 'page' and 'resource' flows, except they are > > now distinguished by a new DMA_ATTR_MMIO instead of by callchain. Both > > flows use the same phys_addr_t. > > > > When DMA_ATTR_MMIO is specified things work similar to the existing > > 'resource' flow. kmap_local_pfn(), phys_to_virt(), phys_to_page(), > > pfn_valid(), etc are never called on the phys_addr_t. This requires > > rejecting any configuration that would need swiotlb. CPU cache > > flushing is not required, and avoided, as ATTR_MMIO also indicates the > > address have no cacheable mappings. This effectively removes any > > DMA API side requirement to have struct page when DMA_ATTR_MMIO is > > used. > > > > In the !DMA_ATTR_MMIO mode things work similarly to the 'page' flow, > > except on the common path of no cache flush, no swiotlb it never > > touches a struct page. When cache flushing or swiotlb copying > > kmap_local_pfn()/phys_to_virt() are used to get a KVA for CPU > > usage. This was already the case on the unmap side, now the map side > > is symmetric. > > > > Callers are adjusted to set DMA_ATTR_MMIO. Existing 'resource' users > > must set it. The existing struct page based MEMORY_DEVICE_PCI_P2PDMA > > path must also set it. This corrects some existing bugs where iommu > > mappings for P2P MMIO were improperly marked IOMMU_CACHE. > > > > Since ATTR_MMIO is made to work with all the existing DMA map entry > > points, particularly dma_iova_link(), this finally allows a way to use > > the new DMA API to map PCI P2P MMIO without creating struct page. The > > VFIO DMABUF series demonstrates how this works. This is intended to > > replace the incorrect driver use of dma_map_resource() on PCI BAR > > addresses. > > > > This series does the core code and modern flows. A followup series > > will give the same treatment to the legacy dma_ops implementation. > > Applied patches 1-13 into dma-mapping-for-next branch. Let's check if it > works fine in linux-next. Thanks a lot. > > Best regards > -- > Marek Szyprowski, PhD > Samsung R&D Institute Poland > >