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 <leo...@nvidia.com> > > > > 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.l...@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.l...@kernel.org/ > > * Fixed kbuild error with mismatch in kmsan function declaration due to > > rebase error. > > v3: https://lore.kernel.org/all/cover.1755193625.git.l...@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.l...@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.l...@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.l...@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 > >
