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Message-ID: <20250828115729.GA10073@unreal> Date: Thu, 28 Aug 2025 14:57:29 +0300 From: Leon Romanovsky <leon@...nel.org> To: Marek Szyprowski <m.szyprowski@...sung.com> Cc: Jason Gunthorpe <jgg@...dia.com>, Abdiel Janulgue <abdiel.janulgue@...il.com>, Alexander Potapenko <glider@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>, iommu@...ts.linux.dev, Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>, Jonathan Corbet <corbet@....net>, Juergen Gross <jgross@...e.com>, kasan-dev@...glegroups.com, Keith Busch <kbusch@...nel.org>, linux-block@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-nvme@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org, linux-trace-kernel@...r.kernel.org, Madhavan Srinivasan <maddy@...ux.ibm.com>, Masami Hiramatsu <mhiramat@...nel.org>, Michael Ellerman <mpe@...erman.id.au>, "Michael S. Tsirkin" <mst@...hat.com>, Miguel Ojeda <ojeda@...nel.org>, Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org, Sagi Grimberg <sagi@...mberg.me>, Stefano Stabellini <sstabellini@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>, xen-devel@...ts.xenproject.org Subject: Re: [PATCH v4 00/16] dma-mapping: migrate to physical address-based API On Tue, Aug 19, 2025 at 08:36:44PM +0300, Leon Romanovsky wrote: > Changelog: > v4: > * 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 cachable DRAM > - struct page MEMORY_DEVICE_PCI_P2PDMA PCI peer to peer non-cachable > MMIO > - struct page-less PCI peer to peer non-cachable MMIO > - struct page-less "resource" MMIO > > Overall this gets much closer to Matthew's long term wish for > struct-pageless IO to cachable 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 cachable 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. > > Thanks > > Leon Romanovsky (16): > dma-mapping: introduce new DMA attribute to indicate MMIO memory > iommu/dma: implement DMA_ATTR_MMIO for dma_iova_link(). > dma-debug: refactor to use physical addresses for page mapping > dma-mapping: rename trace_dma_*map_page to trace_dma_*map_phys > iommu/dma: rename iommu_dma_*map_page to iommu_dma_*map_phys > iommu/dma: extend iommu_dma_*map_phys API to handle MMIO memory > dma-mapping: convert dma_direct_*map_page to be phys_addr_t based > kmsan: convert kmsan_handle_dma to use physical addresses > dma-mapping: handle MMIO flow in dma_map|unmap_page > xen: swiotlb: Open code map_resource callback > dma-mapping: export new dma_*map_phys() interface > mm/hmm: migrate to physical address-based DMA mapping API > mm/hmm: properly take MMIO path > block-dma: migrate to dma_map_phys instead of map_page > block-dma: properly take MMIO path > nvme-pci: unmap MMIO pages with appropriate interface > > Documentation/core-api/dma-api.rst | 4 +- > Documentation/core-api/dma-attributes.rst | 18 ++++ > arch/powerpc/kernel/dma-iommu.c | 4 +- > block/blk-mq-dma.c | 15 ++- > drivers/iommu/dma-iommu.c | 61 +++++------ > drivers/nvme/host/pci.c | 18 +++- > drivers/virtio/virtio_ring.c | 4 +- > drivers/xen/swiotlb-xen.c | 21 +++- > include/linux/blk-mq-dma.h | 6 +- > include/linux/blk_types.h | 2 + > include/linux/dma-direct.h | 2 - > include/linux/dma-map-ops.h | 8 +- > include/linux/dma-mapping.h | 33 ++++++ > include/linux/iommu-dma.h | 11 +- > include/linux/kmsan.h | 9 +- > include/trace/events/dma.h | 9 +- > kernel/dma/debug.c | 71 ++++--------- > kernel/dma/debug.h | 37 ++----- > kernel/dma/direct.c | 22 +--- > kernel/dma/direct.h | 52 ++++++---- > kernel/dma/mapping.c | 117 +++++++++++++--------- > kernel/dma/ops_helpers.c | 6 +- > mm/hmm.c | 19 ++-- > mm/kmsan/hooks.c | 5 +- > rust/kernel/dma.rs | 3 + > tools/virtio/linux/kmsan.h | 2 +- > 26 files changed, 305 insertions(+), 254 deletions(-) Marek, So what are the next steps here? This series is pre-requirement for the VFIO MMIO patches. Thanks > > -- > 2.50.1 > >
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