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Message-ID: <26bd901a-0812-492d-9736-4a7bb2e6d6b4@samsung.com> Date: Mon, 1 Sep 2025 23:47:59 +0200 From: Marek Szyprowski <m.szyprowski@...sung.com> To: Leon Romanovsky <leon@...nel.org> 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 28.08.2025 13:57, Leon Romanovsky wrote: > 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. I waited a bit with a hope to get a comment from Robin. It looks that there is no other alternative for the phys addr in the struct page removal process. I would like to give those patches a try in linux-next, but in meantime I tested it on my test farm and found a regression in dma_map_resource() handling. Namely the dma_map_resource() is no longer possible with size not aligned to kmalloc()'ed buffer, as dma_direct_map_phys() calls dma_kmalloc_needs_bounce(), which in turn calls dma_kmalloc_size_aligned(). It looks that the check for !(attrs & DMA_ATTR_MMIO) should be moved one level up in dma_direct_map_phys(). Here is the log: ------------[ cut here ]------------ dma-pl330 fe550000.dma-controller: DMA addr 0x00000000fe410024+4 overflow (mask ffffffff, bus limit 0). WARNING: kernel/dma/direct.h:116 at dma_map_phys+0x3a4/0x3ec, CPU#1: speaker-test/405 Modules linked in: ... CPU: 1 UID: 0 PID: 405 Comm: speaker-test Not tainted 6.17.0-rc4-next-20250901+ #10958 PREEMPT Hardware name: Hardkernel ODROID-M1 (DT) pstate: 604000c9 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : dma_map_phys+0x3a4/0x3ec lr : dma_map_phys+0x3a4/0x3ec ... Call trace: dma_map_phys+0x3a4/0x3ec (P) dma_map_resource+0x14/0x20 pl330_prep_slave_fifo+0x78/0xd0 pl330_prep_dma_cyclic+0x70/0x2b0 snd_dmaengine_pcm_trigger+0xec/0x8bc [snd_pcm_dmaengine] dmaengine_pcm_trigger+0x18/0x24 [snd_soc_core] snd_soc_pcm_component_trigger+0x164/0x208 [snd_soc_core] soc_pcm_trigger+0xe4/0x1ec [snd_soc_core] snd_pcm_do_start+0x44/0x70 [snd_pcm] snd_pcm_action_single+0x48/0xa4 [snd_pcm] snd_pcm_action+0x7c/0x98 [snd_pcm] snd_pcm_action_lock_irq+0x48/0xb4 [snd_pcm] snd_pcm_common_ioctl+0xf00/0x1f1c [snd_pcm] snd_pcm_ioctl+0x30/0x48 [snd_pcm] __arm64_sys_ioctl+0xac/0x104 invoke_syscall+0x48/0x110 el0_svc_common.constprop.0+0x40/0xe8 do_el0_svc+0x20/0x2c el0_svc+0x4c/0x160 el0t_64_sync_handler+0xa0/0xe4 el0t_64_sync+0x198/0x19c irq event stamp: 6596 hardirqs last enabled at (6595): [<ffff800081344624>] _raw_spin_unlock_irqrestore+0x74/0x78 hardirqs last disabled at (6596): [<ffff8000813439b0>] _raw_spin_lock_irq+0x78/0x7c softirqs last enabled at (6076): [<ffff8000800c2294>] handle_softirqs+0x4c4/0x4dc softirqs last disabled at (6071): [<ffff800080010690>] __do_softirq+0x14/0x20 ---[ end trace 0000000000000000 ]--- rockchip-i2s-tdm fe410000.i2s: ASoC error (-12): at soc_component_trigger() on fe410000.i2s Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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