Linaro-mm-sig November 2025

linaro-mm-sig@lists.linaro.org

19 participants
100 discussions

Re: [PATCH net-next v6 0/6] Add AF_XDP zero copy support

by patchwork-bot+netdevbpf＠kernel.org

Hello: This series was applied to netdev/net-next.git (main) by Paolo Abeni <pabeni(a)redhat.com>: On Tue, 18 Nov 2025 19:25:36 +0530 you wrote: > This series adds AF_XDP zero coppy support to icssg driver. > > Tests were performed on AM64x-EVM with xdpsock application [1]. > > A clear improvement is seen Transmit (txonly) and receive (rxdrop) > for 64 byte packets. 1500 byte test seems to be limited by line > rate (1G link) so no improvement seen there in packet rate > > [...] Here is the summary with links: - [net-next,v6,1/6] net: ti: icssg-prueth: Add functions to create and destroy Rx/Tx queues https://git.kernel.org/netdev/net-next/c/41dde7f1d013 - [net-next,v6,2/6] net: ti: icssg-prueth: Add XSK pool helpers https://git.kernel.org/netdev/net-next/c/7dfd7597911f - [net-next,v6,3/6] net: ti: icssg-prueth: Add AF_XDP zero copy for TX https://git.kernel.org/netdev/net-next/c/8756ef2eb078 - [net-next,v6,4/6] net: ti: icssg-prueth: Make emac_run_xdp function independent of page https://git.kernel.org/netdev/net-next/c/121133163c9f - [net-next,v6,5/6] net: ti: icssg-prueth: Add AF_XDP zero copy for RX https://git.kernel.org/netdev/net-next/c/7a64bb388df3 - [net-next,v6,6/6] net: ti: icssg-prueth: Enable zero copy in XDP features https://git.kernel.org/netdev/net-next/c/c6a1ec1870e6 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html

2 months, 1 week

Re: [PATCH 02/18] dma-buf: protected fence ops by RCU v3

by Christian König

On 11/18/25 17:03, Tvrtko Ursulin wrote: >>>> @@ -448,13 +465,19 @@ dma_fence_is_signaled_locked(struct dma_fence *fence) >>>> static inline bool >>>> dma_fence_is_signaled(struct dma_fence *fence) >>>> { >>>> + const struct dma_fence_ops *ops; >>>> + >>>> if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) >>>> return true; >>>> - if (fence->ops->signaled && fence->ops->signaled(fence)) { >>>> + rcu_read_lock(); >>>> + ops = rcu_dereference(fence->ops); >>>> + if (ops->signaled && ops->signaled(fence)) { >>>> + rcu_read_unlock(); >>> >>> With the unlocked version two threads could race and one could make the fence->lock go away just around here, before the dma_fence_signal below will take it. It seems it is only safe to rcu_read_unlock before signaling if using the embedded fence (later in the series). Can you think of a downside to holding the rcu read lock to after signaling? that would make it safe I think. >> >> Well it's good to talk about it but I think that it is not necessary to protect the lock in this particular case. >> >> See the RCU protection is only for the fence->ops pointer, but the lock can be taken way after the fence is already signaled. >> >> That's why I came up with the patch to move the lock into the fence in the first place. > > Right. And you think there is nothing to gain with the option of keeping the rcu_read_unlock() to after signalling? Ie. why not plug a potential race if we can for no negative effect. I thought quite a bit over that, but at least of hand I can't come up with a reason why we should do this. The signaling path doesn't need the RCU read side lock as far as I can see. Regards, Christian. > > Regards, > > Tvrtko

2 months, 1 week

[RFC PATCH 0/2] locking/ww_mutex, dma-buf/dma-resv: Improve detection of unheld locks

by Thomas Hellström

WW mutexes and dma-resv objects, which embed them, typically have a number of locks belocking to the same lock class. However code using them typically want to verify the locking on object granularity, not lock-class granularity. This series add ww_mutex functions to facilitate that, (patch 1) and utilizes these functions in the dma-resv lock checks. Thomas Hellström (2): kernel/locking/ww_mutex: Add per-lock lock-check helpers dma-buf/dma-resv: Improve the dma-resv lockdep checks include/linux/dma-resv.h | 7 +++++-- include/linux/ww_mutex.h | 18 ++++++++++++++++++ kernel/locking/mutex.c | 10 ++++++++++ 3 files changed, 33 insertions(+), 2 deletions(-) -- 2.51.1

2 months, 1 week

[PATCH v8 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf

by Leon Romanovsky

Changelog: v8: * Fixed spelling errors in p2pdma documentation file. * Added vdev->pci_ops check for NULL in vfio_pci_core_feature_dma_buf(). * Simplified the nvgrace_get_dmabuf_phys() function. * Added extra check in pcim_p2pdma_provider() to catch missing call to pcim_p2pdma_init(). v7: https://patch.msgid.link/20251106-dmabuf-vfio-v7-0-2503bf390699@nvidia.com * Dropped restore_revoke flag and added vfio_pci_dma_buf_move to reverse loop. * Fixed spelling errors in documentation patch. * Rebased on top of v6.18-rc3. * Added include to stddef.h to vfio.h, to keep uapi header file independent. v6: https://patch.msgid.link/20251102-dmabuf-vfio-v6-0-d773cff0db9f@nvidia.com * Fixed wrong error check from pcim_p2pdma_init(). * Documented pcim_p2pdma_provider() function. * Improved commit messages. * Added VFIO DMA-BUF selftest, not sent yet. * Added __counted_by(nr_ranges) annotation to struct vfio_device_feature_dma_buf. * Fixed error unwind when dma_buf_fd() fails. * Document latest changes to p2pmem. * Removed EXPORT_SYMBOL_GPL from pci_p2pdma_map_type. * Moved DMA mapping logic to DMA-BUF. * Removed types patch to avoid dependencies between subsystems. * Moved vfio_pci_dma_buf_move() in err_undo block. * Added nvgrace patch. v5: https://lore.kernel.org/all/cover.1760368250.git.leon@kernel.org * Rebased on top of v6.18-rc1. * Added more validation logic to make sure that DMA-BUF length doesn't overflow in various scenarios. * Hide kernel config from the users. * Fixed type conversion issue. DMA ranges are exposed with u64 length, but DMA-BUF uses "unsigned int" as a length for SG entries. * Added check to prevent from VFIO drivers which reports BAR size different from PCI, do not use DMA-BUF functionality. v4: https://lore.kernel.org/all/cover.1759070796.git.leon@kernel.org * Split pcim_p2pdma_provider() to two functions, one that initializes array of providers and another to return right provider pointer. v3: https://lore.kernel.org/all/cover.1758804980.git.leon@kernel.org * Changed pcim_p2pdma_enable() to be pcim_p2pdma_provider(). * Cache provider in vfio_pci_dma_buf struct instead of BAR index. * Removed misleading comment from pcim_p2pdma_provider(). * Moved MMIO check to be in pcim_p2pdma_provider(). v2: https://lore.kernel.org/all/cover.1757589589.git.leon@kernel.org/ * Added extra patch which adds new CONFIG, so next patches can reuse * it. * Squashed "PCI/P2PDMA: Remove redundant bus_offset from map state" into the other patch. * Fixed revoke calls to be aligned with true->false semantics. * Extended p2pdma_providers to be per-BAR and not global to whole * device. * Fixed possible race between dmabuf states and revoke. * Moved revoke to PCI BAR zap block. v1: https://lore.kernel.org/all/cover.1754311439.git.leon@kernel.org * Changed commit messages. * Reused DMA_ATTR_MMIO attribute. * Returned support for multiple DMA ranges per-dMABUF. v0: https://lore.kernel.org/all/cover.1753274085.git.leonro@nvidia.com --------------------------------------------------------------------------- Based on "[PATCH v6 00/16] dma-mapping: migrate to physical address-based API" https://lore.kernel.org/all/cover.1757423202.git.leonro@nvidia.com/ series. --------------------------------------------------------------------------- This series extends the VFIO PCI subsystem to support exporting MMIO regions from PCI device BARs as dma-buf objects, enabling safe sharing of non-struct page memory with controlled lifetime management. This allows RDMA and other subsystems to import dma-buf FDs and build them into memory regions for PCI P2P operations. The series supports a use case for SPDK where a NVMe device will be owned by SPDK through VFIO but interacting with a RDMA device. The RDMA device may directly access the NVMe CMB or directly manipulate the NVMe device's doorbell using PCI P2P. However, as a general mechanism, it can support many other scenarios with VFIO. This dmabuf approach can be usable by iommufd as well for generic and safe P2P mappings. In addition to the SPDK use-case mentioned above, the capability added in this patch series can also be useful when a buffer (located in device memory such as VRAM) needs to be shared between any two dGPU devices or instances (assuming one of them is bound to VFIO PCI) as long as they are P2P DMA compatible. The implementation provides a revocable attachment mechanism using dma-buf move operations. MMIO regions are normally pinned as BARs don't change physical addresses, but access is revoked when the VFIO device is closed or a PCI reset is issued. This ensures kernel self-defense against potentially hostile userspace. The series includes significant refactoring of the PCI P2PDMA subsystem to separate core P2P functionality from memory allocation features, making it more modular and suitable for VFIO use cases that don't need struct page support. ----------------------------------------------------------------------- The series is based originally on https://lore.kernel.org/all/20250307052248.405803-1-vivek.kasireddy@intel.c… but heavily rewritten to be based on DMA physical API. ----------------------------------------------------------------------- The WIP branch can be found here: https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=… Thanks --- Jason Gunthorpe (2): PCI/P2PDMA: Document DMABUF model vfio/nvgrace: Support get_dmabuf_phys Leon Romanovsky (7): PCI/P2PDMA: Separate the mmap() support from the core logic PCI/P2PDMA: Simplify bus address mapping API PCI/P2PDMA: Refactor to separate core P2P functionality from memory allocation PCI/P2PDMA: Provide an access to pci_p2pdma_map_type() function dma-buf: provide phys_vec to scatter-gather mapping routine vfio/pci: Enable peer-to-peer DMA transactions by default vfio/pci: Add dma-buf export support for MMIO regions Vivek Kasireddy (2): vfio: Export vfio device get and put registration helpers vfio/pci: Share the core device pointer while invoking feature functions Documentation/driver-api/pci/p2pdma.rst | 95 +++++++--- block/blk-mq-dma.c | 2 +- drivers/dma-buf/dma-buf.c | 235 ++++++++++++++++++++++++ drivers/iommu/dma-iommu.c | 4 +- drivers/pci/p2pdma.c | 186 ++++++++++++++----- drivers/vfio/pci/Kconfig | 3 + drivers/vfio/pci/Makefile | 1 + drivers/vfio/pci/nvgrace-gpu/main.c | 56 ++++++ drivers/vfio/pci/vfio_pci.c | 5 + drivers/vfio/pci/vfio_pci_config.c | 22 ++- drivers/vfio/pci/vfio_pci_core.c | 53 ++++-- drivers/vfio/pci/vfio_pci_dmabuf.c | 315 ++++++++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_priv.h | 23 +++ drivers/vfio/vfio_main.c | 2 + include/linux/dma-buf.h | 18 ++ include/linux/pci-p2pdma.h | 120 +++++++----- include/linux/vfio.h | 2 + include/linux/vfio_pci_core.h | 42 +++++ include/uapi/linux/vfio.h | 28 +++ kernel/dma/direct.c | 4 +- mm/hmm.c | 2 +- 21 files changed, 1078 insertions(+), 140 deletions(-) --- base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa change-id: 20251016-dmabuf-vfio-6cef732adf5a Best regards, -- Leon Romanovsky <leonro(a)nvidia.com>

2 months, 1 week

[PATCH v9 00/11] vfio/pci: Allow MMIO regions to be exported through dma-buf

by Leon Romanovsky

Changelog: v9: * Added Reviewed-by tags. * Fixes to p2pdma documentation. * Renamed dma_buf_map and unmap. * Moved them to separate file. * Used nvgrace_gpu_memregion() function instead of open-coded variant. * Paired get_file_active() with fput(). v8: https://patch.msgid.link/20251111-dmabuf-vfio-v8-0-fd9aa5df478f@nvidia.com * Fixed spelling errors in p2pdma documentation file. * Added vdev->pci_ops check for NULL in vfio_pci_core_feature_dma_buf(). * Simplified the nvgrace_get_dmabuf_phys() function. * Added extra check in pcim_p2pdma_provider() to catch missing call to pcim_p2pdma_init(). v7: https://patch.msgid.link/20251106-dmabuf-vfio-v7-0-2503bf390699@nvidia.com * Dropped restore_revoke flag and added vfio_pci_dma_buf_move to reverse loop. * Fixed spelling errors in documentation patch. * Rebased on top of v6.18-rc3. * Added include to stddef.h to vfio.h, to keep uapi header file independent. v6: https://patch.msgid.link/20251102-dmabuf-vfio-v6-0-d773cff0db9f@nvidia.com * Fixed wrong error check from pcim_p2pdma_init(). * Documented pcim_p2pdma_provider() function. * Improved commit messages. * Added VFIO DMA-BUF selftest, not sent yet. * Added __counted_by(nr_ranges) annotation to struct vfio_device_feature_dma_buf. * Fixed error unwind when dma_buf_fd() fails. * Document latest changes to p2pmem. * Removed EXPORT_SYMBOL_GPL from pci_p2pdma_map_type. * Moved DMA mapping logic to DMA-BUF. * Removed types patch to avoid dependencies between subsystems. * Moved vfio_pci_dma_buf_move() in err_undo block. * Added nvgrace patch. v5: https://lore.kernel.org/all/cover.1760368250.git.leon@kernel.org * Rebased on top of v6.18-rc1. * Added more validation logic to make sure that DMA-BUF length doesn't overflow in various scenarios. * Hide kernel config from the users. * Fixed type conversion issue. DMA ranges are exposed with u64 length, but DMA-BUF uses "unsigned int" as a length for SG entries. * Added check to prevent from VFIO drivers which reports BAR size different from PCI, do not use DMA-BUF functionality. v4: https://lore.kernel.org/all/cover.1759070796.git.leon@kernel.org * Split pcim_p2pdma_provider() to two functions, one that initializes array of providers and another to return right provider pointer. v3: https://lore.kernel.org/all/cover.1758804980.git.leon@kernel.org * Changed pcim_p2pdma_enable() to be pcim_p2pdma_provider(). * Cache provider in vfio_pci_dma_buf struct instead of BAR index. * Removed misleading comment from pcim_p2pdma_provider(). * Moved MMIO check to be in pcim_p2pdma_provider(). v2: https://lore.kernel.org/all/cover.1757589589.git.leon@kernel.org/ * Added extra patch which adds new CONFIG, so next patches can reuse * it. * Squashed "PCI/P2PDMA: Remove redundant bus_offset from map state" into the other patch. * Fixed revoke calls to be aligned with true->false semantics. * Extended p2pdma_providers to be per-BAR and not global to whole * device. * Fixed possible race between dmabuf states and revoke. * Moved revoke to PCI BAR zap block. v1: https://lore.kernel.org/all/cover.1754311439.git.leon@kernel.org * Changed commit messages. * Reused DMA_ATTR_MMIO attribute. * Returned support for multiple DMA ranges per-dMABUF. v0: https://lore.kernel.org/all/cover.1753274085.git.leonro@nvidia.com --------------------------------------------------------------------------- Based on "[PATCH v6 00/16] dma-mapping: migrate to physical address-based API" https://lore.kernel.org/all/cover.1757423202.git.leonro@nvidia.com/ series. --------------------------------------------------------------------------- This series extends the VFIO PCI subsystem to support exporting MMIO regions from PCI device BARs as dma-buf objects, enabling safe sharing of non-struct page memory with controlled lifetime management. This allows RDMA and other subsystems to import dma-buf FDs and build them into memory regions for PCI P2P operations. The series supports a use case for SPDK where a NVMe device will be owned by SPDK through VFIO but interacting with a RDMA device. The RDMA device may directly access the NVMe CMB or directly manipulate the NVMe device's doorbell using PCI P2P. However, as a general mechanism, it can support many other scenarios with VFIO. This dmabuf approach can be usable by iommufd as well for generic and safe P2P mappings. In addition to the SPDK use-case mentioned above, the capability added in this patch series can also be useful when a buffer (located in device memory such as VRAM) needs to be shared between any two dGPU devices or instances (assuming one of them is bound to VFIO PCI) as long as they are P2P DMA compatible. The implementation provides a revocable attachment mechanism using dma-buf move operations. MMIO regions are normally pinned as BARs don't change physical addresses, but access is revoked when the VFIO device is closed or a PCI reset is issued. This ensures kernel self-defense against potentially hostile userspace. The series includes significant refactoring of the PCI P2PDMA subsystem to separate core P2P functionality from memory allocation features, making it more modular and suitable for VFIO use cases that don't need struct page support. ----------------------------------------------------------------------- The series is based originally on https://lore.kernel.org/all/20250307052248.405803-1-vivek.kasireddy@intel.c… but heavily rewritten to be based on DMA physical API. ----------------------------------------------------------------------- The WIP branch can be found here: https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=… Thanks --- Jason Gunthorpe (2): PCI/P2PDMA: Document DMABUF model vfio/nvgrace: Support get_dmabuf_phys Leon Romanovsky (7): PCI/P2PDMA: Separate the mmap() support from the core logic PCI/P2PDMA: Simplify bus address mapping API PCI/P2PDMA: Refactor to separate core P2P functionality from memory allocation PCI/P2PDMA: Provide an access to pci_p2pdma_map_type() function dma-buf: provide phys_vec to scatter-gather mapping routine vfio/pci: Enable peer-to-peer DMA transactions by default vfio/pci: Add dma-buf export support for MMIO regions Vivek Kasireddy (2): vfio: Export vfio device get and put registration helpers vfio/pci: Share the core device pointer while invoking feature functions Documentation/driver-api/pci/p2pdma.rst | 97 +++++++--- block/blk-mq-dma.c | 2 +- drivers/dma-buf/Makefile | 2 +- drivers/dma-buf/dma-buf-mapping.c | 248 +++++++++++++++++++++++++ drivers/iommu/dma-iommu.c | 4 +- drivers/pci/p2pdma.c | 186 ++++++++++++++----- drivers/vfio/pci/Kconfig | 3 + drivers/vfio/pci/Makefile | 1 + drivers/vfio/pci/nvgrace-gpu/main.c | 52 ++++++ drivers/vfio/pci/vfio_pci.c | 5 + drivers/vfio/pci/vfio_pci_config.c | 22 ++- drivers/vfio/pci/vfio_pci_core.c | 53 ++++-- drivers/vfio/pci/vfio_pci_dmabuf.c | 316 ++++++++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_priv.h | 23 +++ drivers/vfio/vfio_main.c | 2 + include/linux/dma-buf-mapping.h | 17 ++ include/linux/dma-buf.h | 11 ++ include/linux/pci-p2pdma.h | 120 +++++++----- include/linux/vfio.h | 2 + include/linux/vfio_pci_core.h | 42 +++++ include/uapi/linux/vfio.h | 28 +++ kernel/dma/direct.c | 4 +- mm/hmm.c | 2 +- 23 files changed, 1101 insertions(+), 141 deletions(-) --- base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa change-id: 20251016-dmabuf-vfio-6cef732adf5a Best regards, -- Leon Romanovsky <leonro(a)nvidia.com>

2 months, 1 week

Re: [PATCH v8 10/11] vfio/pci: Add dma-buf export support for MMIO regions

by Jason Gunthorpe

On Tue, Nov 18, 2025 at 11:56:14PM +0000, Tian, Kevin wrote: > > > > + down_write(&vdev->memory_lock); > > > > + list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) > > > > { > > > > + if (!get_file_active(&priv->dmabuf->file)) > > > > + continue; > > > > + > > > > + dma_resv_lock(priv->dmabuf->resv, NULL); > > > > + list_del_init(&priv->dmabufs_elm); > > > > + priv->vdev = NULL; > > > > + priv->revoked = true; > > > > + dma_buf_move_notify(priv->dmabuf); > > > > + dma_resv_unlock(priv->dmabuf->resv); > > > > + vfio_device_put_registration(&vdev->vdev); > > > > + fput(priv->dmabuf->file); > > > > > > dma_buf_put(priv->dmabuf), consistent with other places. > > > > Someone else said this, I don't agree, the above got the get via > > > > get_file_active() instead of a dma_buf version.. > > > > So we should pair with get_file_active() vs fput(). > > > > Christian rejected the idea of adding a dmabuf wrapper for > > get_file_active(), oh well. > > Okay then vfio_pci_dma_buf_move() should be changed. It uses > get_file_active() to pair dma_buf_put(). Makes sense, Leon can you fix it? Thanks, Jason

2 months, 1 week

Re: [PATCH v2 02/20] drm/ttm: rework pipelined eviction fence handling

by Thomas Hellström

Hi, Pierre-Eric On Thu, 2025-11-13 at 17:05 +0100, Pierre-Eric Pelloux-Prayer wrote: > Until now ttm stored a single pipelined eviction fence which means > drivers had to use a single entity for these evictions. > > To lift this requirement, this commit allows up to 8 entities to > be used. > > Ideally a dma_resv object would have been used as a container of > the eviction fences, but the locking rules makes it complex. > dma_resv all have the same ww_class, which means "Attempting to > lock more mutexes after ww_acquire_done." is an error. > > One alternative considered was to introduced a 2nd ww_class for > specific resv to hold a single "transient" lock (= the resv lock > would only be held for a short period, without taking any other > locks). Wouldn't it be possible to use lockdep_set_class_and_name() to modify the resv lock class for these particular resv objects after they are allocated? Reusing the resv code certainly sounds attractive. Thanks, Thomas

2 months, 1 week

Re: [PATCH v8 09/11] vfio/pci: Enable peer-to-peer DMA transactions by default

by Leon Romanovsky

On Wed, Nov 19, 2025 at 12:02:02AM +0000, Tian, Kevin wrote: > > From: Keith Busch <kbusch(a)kernel.org> > > Sent: Wednesday, November 19, 2025 4:19 AM > > > > On Tue, Nov 18, 2025 at 07:18:36AM +0000, Tian, Kevin wrote: > > > > From: Leon Romanovsky <leon(a)kernel.org> > > > > Sent: Tuesday, November 11, 2025 5:58 PM > > > > > > > > From: Leon Romanovsky <leonro(a)nvidia.com> > > > > > > not required with only your own s-o-b > > > > That's automatically appended when the sender and signer don't match. > > It's not uncommon for developers to send from a kernel.org email but > > sign off with a corporate account, or the other way around. > > Good to know. Yes, in addition, I used to separate between code authorship and my open-source activity. Code belongs to my employer and this is why corporate address is used as an author, but all emails and communications are coming from my kernel.org account. Thanks

2 months, 1 week

Re: [PATCH v8 06/11] dma-buf: provide phys_vec to scatter-gather mapping routine

by Leon Romanovsky

On Wed, Nov 19, 2025 at 05:54:55AM +0000, Tian, Kevin wrote: > > From: Leon Romanovsky <leon(a)kernel.org> > > Sent: Tuesday, November 11, 2025 5:58 PM > > + > > + if (dma->state && dma_use_iova(dma->state)) { > > + WARN_ON_ONCE(mapped_len != size); > > then "goto err_unmap_dma". It never should happen, there is no need to provide error unwind to something that you won't get. > > Reviewed-by: Kevin Tian <kevin.tian(a)intel.com> Thanks

2 months, 1 week

Re: [PATCH v8 06/11] dma-buf: provide phys_vec to scatter-gather mapping routine

by Leon Romanovsky

On Tue, Nov 18, 2025 at 04:06:11PM -0800, Nicolin Chen wrote: > On Tue, Nov 11, 2025 at 11:57:48AM +0200, Leon Romanovsky wrote: > > From: Leon Romanovsky <leonro(a)nvidia.com> > > > > Add dma_buf_map() and dma_buf_unmap() helpers to convert an array of > > MMIO physical address ranges into scatter-gather tables with proper > > DMA mapping. > > > > These common functions are a starting point and support any PCI > > drivers creating mappings from their BAR's MMIO addresses. VFIO is one > > case, as shortly will be RDMA. We can review existing DRM drivers to > > refactor them separately. We hope this will evolve into routines to > > help common DRM that include mixed CPU and MMIO mappings. > > > > Compared to the dma_map_resource() abuse this implementation handles > > the complicated PCI P2P scenarios properly, especially when an IOMMU > > is enabled: > > > > - Direct bus address mapping without IOVA allocation for > > PCI_P2PDMA_MAP_BUS_ADDR, using pci_p2pdma_bus_addr_map(). This > > happens if the IOMMU is enabled but the PCIe switch ACS flags allow > > transactions to avoid the host bridge. > > > > Further, this handles the slightly obscure, case of MMIO with a > > phys_addr_t that is different from the physical BAR programming > > (bus offset). The phys_addr_t is converted to a dma_addr_t and > > accommodates this effect. This enables certain real systems to > > work, especially on ARM platforms. > > > > - Mapping through host bridge with IOVA allocation and DMA_ATTR_MMIO > > attribute for MMIO memory regions (PCI_P2PDMA_MAP_THRU_HOST_BRIDGE). > > This happens when the IOMMU is enabled and the ACS flags are forcing > > all traffic to the IOMMU - ie for virtualization systems. > > > > - Cases where P2P is not supported through the host bridge/CPU. The > > P2P subsystem is the proper place to detect this and block it. > > > > Helper functions fill_sg_entry() and calc_sg_nents() handle the > > scatter-gather table construction, splitting large regions into > > UINT_MAX-sized chunks to fit within sg->length field limits. > > > > Since the physical address based DMA API forbids use of the CPU list > > of the scatterlist this will produce a mangled scatterlist that has > > a fully zero-length and NULL'd CPU list. The list is 0 length, > > all the struct page pointers are NULL and zero sized. This is stronger > > and more robust than the existing mangle_sg_table() technique. It is > > a future project to migrate DMABUF as a subsystem away from using > > scatterlist for this data structure. > > > > Tested-by: Alex Mastro <amastro(a)fb.com> > > Tested-by: Nicolin Chen <nicolinc(a)nvidia.com> > > Signed-off-by: Leon Romanovsky <leonro(a)nvidia.com> > > Reviewed-by: Nicolin Chen <nicolinc(a)nvidia.com> > > With a nit: > > > +err_unmap_dma: > > + if (!i || !dma->state) { > > + ; /* Do nothing */ > > + } else if (dma_use_iova(dma->state)) { > > + dma_iova_destroy(attach->dev, dma->state, mapped_len, dir, > > + DMA_ATTR_MMIO); > > + } else { > > + for_each_sgtable_dma_sg(&dma->sgt, sgl, i) > > + dma_unmap_phys(attach->dev, sg_dma_address(sgl), > > + sg_dma_len(sgl), dir, DMA_ATTR_MMIO); > > Would it be safer to skip dma_unmap_phys() the range [i, nents)? [i, nents) is not supposed to be in SG list which we are iterating. Thanks

2 months, 1 week

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2016

2015

2014

2013

2012

2011

Linaro-mm-sig November 2025