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Re: [PATCH v6 09/12] dma-buf: heaps: Add support for Tegra VPR

by Rob Herring

On Fri, Sep 04, 2026 at 12:45:00PM +0200, Thierry Reding wrote: > From: Thierry Reding <treding(a)nvidia.com> > > NVIDIA Tegra SoCs commonly define a Video-Protection-Region, which is a > region of memory dedicated to content-protected video decode and > playback. This memory cannot be accessed by the CPU and only certain > hardware devices have access to it. > > Expose the VPR as a DMA heap so that applications and drivers can > allocate buffers from this region for use-cases that require this kind > of protected memory. > > VPR has a few very critical peculiarities. First, it must be a single > contiguous region of memory (there is a single pair of registers that > set the base address and size of the region), which is configured by > calling back into the secure monitor. The memory region also needs to > quite large for some use-cases because it needs to fit multiple video > frames (8K video should be supported), so VPR sizes of ~2 GiB are > expected. However, some devices cannot afford to reserve this amount > of memory for a particular use-case, and therefore the VPR must be > resizable. > > Unfortunately, resizing the VPR is slightly tricky because the GPU found > on Tegra SoCs must be in reset during the VPR resize operation. This is > currently implemented by freezing all userspace processes and calling > invoking the GPU's freeze() implementation, resizing and the thawing the > GPU and userspace processes. This is quite heavy-handed, so eventually > it might be better to implement thawing/freezing in the GPU driver in > such a way that they block accesses to the GPU so that the VPR resize > operation can happen without suspending all userspace. > > In order to balance the memory usage versus the amount of resizing that > needs to happen, the VPR is divided into multiple chunks. Each chunk is > implemented as a section of the CMA area that is completely allocated on > first use to guarantee the contiguity of the VPR. Once all buffers from > a chunk have been freed, the subsection is freed and the memory returned > to the system. > > The Tegra VPR driver is split into two pieces: one tiny part of the > driver is always built-in and sets up the CMA area during early boot, > whereas the second, larger, part provides the DMA heap implementation > and can be built as a module. Note that tearing down VPR is tricky and > usually not necessary, so it can currently not be unloaded. > > Signed-off-by: Thierry Reding <treding(a)nvidia.com> > --- > Changes in v6: > - split code into a small core and the main chunk so the latter can be > built as a module > > Changes in v5: > - use newly introduced cma_alloc_at() and work with a single CMA area > - setup CMA early and initialize VPR later during boot > - remove some unused variables > - use kalloc_objs() > > Changes in v4: > - address Sashiko and checkpatch comments > - fully remove from linear map while chunks are allocated > - improve error handling > - remove freezer support > > Changes in v3: > - use set_memory_device() and set_memory_normal() helpers > - use kzalloc_obj() instead of kzalloc() with sizeof() > > Changes in v2: > - cluster allocations to reduce the number of resize operations > - support cross-chunk allocation > --- > drivers/dma-buf/heaps/Kconfig | 12 + > drivers/dma-buf/heaps/Makefile | 10 + > drivers/dma-buf/heaps/tegra-vpr-init.c | 133 ++++ > drivers/dma-buf/heaps/tegra-vpr.c | 1210 ++++++++++++++++++++++++++++++++ > drivers/dma-buf/heaps/tegra-vpr.h | 73 ++ > include/trace/events/tegra_vpr.h | 57 ++ > 6 files changed, 1495 insertions(+) > > diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig > index bb729e91545c..28d2c0800fb5 100644 > --- a/drivers/dma-buf/heaps/Kconfig > +++ b/drivers/dma-buf/heaps/Kconfig > @@ -20,3 +20,15 @@ config DMABUF_HEAPS_CMA > Choose this option to enable dma-buf CMA heap. This heap is backed > by the Contiguous Memory Allocator (CMA). If your system has these > regions, you should say Y here. > + > +config DMABUF_HEAPS_TEGRA_VPR > + tristate "NVIDIA Tegra Video-Protected-Region DMA-BUF Heap" > + depends on DMABUF_HEAPS && DMA_CMA > + help > + Choose this option to enable Video-Protected-Region (VPR) support on > + a range of NVIDIA Tegra devices. Access to VPR memory is limited to > + a subset of hardware engines and specifically disallowed from the > + CPU. The region can be fixed, in which case no linear mapping exists > + for the memory, or it can be resizable on systems that want to reuse > + the memory for other uses when content-protected video is not played > + back. > diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile > index 974467791032..481fcb78f757 100644 > --- a/drivers/dma-buf/heaps/Makefile > +++ b/drivers/dma-buf/heaps/Makefile > @@ -1,3 +1,13 @@ > # SPDX-License-Identifier: GPL-2.0 > obj-$(CONFIG_DMABUF_HEAPS_SYSTEM) += system_heap.o > obj-$(CONFIG_DMABUF_HEAPS_CMA) += cma_heap.o > + > +# > +# The reserved-memory bits always need to be built-in so that the CMA > +# initialization runs during early boot. The VPR driver itself can be > +# built as a module. > +# > +ifneq ($(CONFIG_DMABUF_HEAPS_TEGRA_VPR),) > +obj-y += tegra-vpr-init.o > +obj-$(CONFIG_DMABUF_HEAPS_TEGRA_VPR) += tegra-vpr.o > +endif > diff --git a/drivers/dma-buf/heaps/tegra-vpr-init.c b/drivers/dma-buf/heaps/tegra-vpr-init.c > new file mode 100644 > index 000000000000..65e917713c6d > --- /dev/null > +++ b/drivers/dma-buf/heaps/tegra-vpr-init.c > @@ -0,0 +1,133 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * DMA-BUF restricted heap exporter for NVIDIA Video-Protection-Region (VPR) > + * > + * Copyright (C) 2024-2026 NVIDIA Corporation > + */ > + > +#define pr_fmt(fmt) "tegra-vpr: " fmt > + > +#include "tegra-vpr.h" > + > +#include <linux/cma.h> > +#include <linux/of_reserved_mem.h> > + > +static DEFINE_MUTEX(vpr_lock); > +static LIST_HEAD_GUARDED(vpr_list, vpr_lock); > + > +static int __init tegra_vpr_node_init(unsigned long offset, > + struct reserved_mem *rmem) > +{ > + struct cma *cma; > + int err; > + > + if (!IS_ALIGNED(rmem->base, SZ_1M)) { > + pr_err("%s: base is not aligned to 1 MiB\n", rmem->name); > + return -EINVAL; > + } > + > + if (!IS_ALIGNED(rmem->size, SZ_1M)) { > + pr_err("%s: size is not aligned to 1 MiB\n", rmem->name); > + return -EINVAL; > + } > + > + err = cma_init_reserved_mem(rmem->base, rmem->size, 0, rmem->name, > + &cma); > + if (err < 0) { > + pr_err("%s: failed to initialize CMA: %d\n", __func__, err); > + return err; > + } > + > + rmem->priv = cma; > + > + return 0; > +} > + > +static struct tegra_vpr *tegra_vpr_lookup(struct cma *cma) > +{ > + struct tegra_vpr *vpr; > + > + mutex_lock(&vpr_lock); > + > + list_for_each_entry(vpr, &vpr_list, list) { > + if (vpr->cma == cma) { > + mutex_unlock(&vpr_lock); > + return vpr; > + } > + } > + > + mutex_unlock(&vpr_lock); > + > + return ERR_PTR(-EPROBE_DEFER); > +} > + > +static int tegra_vpr_device_init(struct reserved_mem *rmem, struct device *dev) > +{ > + const struct dev_pm_ops *pm = dev->driver->pm; > + struct tegra_vpr_device *node; > + struct cma *cma = rmem->priv; > + struct tegra_vpr *vpr; > + > + vpr = tegra_vpr_lookup(cma); > + if (IS_ERR(vpr)) > + return PTR_ERR(vpr); > + > + if (!pm || !pm->freeze || !pm->thaw) > + return -EINVAL; > + > + node = kzalloc_obj(*node, GFP_KERNEL); > + if (!node) > + return -ENOMEM; > + > + INIT_LIST_HEAD(&node->node); > + node->dev = dev; > + > + mutex_lock(&vpr->lock); > + list_add_tail(&node->node, &vpr->devices); > + mutex_unlock(&vpr->lock); > + > + return 0; > +} > + > +static void tegra_vpr_device_release(struct reserved_mem *rmem, > + struct device *dev) > +{ > + struct tegra_vpr_device *node, *tmp; > + struct cma *cma = rmem->priv; > + struct tegra_vpr *vpr; > + > + vpr = tegra_vpr_lookup(cma); > + if (IS_ERR(vpr)) { > + dev_WARN(dev, "failed to find VPR for CMA '%s'\n", > + cma_get_name(cma)); > + return; > + } > + > + mutex_lock(&vpr->lock); > + > + list_for_each_entry_safe(node, tmp, &vpr->devices, node) { > + if (node->dev == dev) { > + list_del(&node->node); > + kfree(node); > + } > + } > + > + mutex_unlock(&vpr->lock); > +} > + > +static const struct reserved_mem_ops tegra_vpr_rmem_ops = { > + .node_init = tegra_vpr_node_init, > + .device_init = tegra_vpr_device_init, > + .device_release = tegra_vpr_device_release, > +}; > + > +RESERVEDMEM_OF_DECLARE(tegra_vpr, "nvidia,tegra-video-protection-region", > + &tegra_vpr_rmem_ops); > + > +void tegra_vpr_add(struct tegra_vpr *vpr) > +{ > + mutex_lock(&vpr_lock); > + list_add_tail(&vpr->list, &vpr_list); > + mutex_unlock(&vpr_lock); > +} > +EXPORT_SYMBOL(tegra_vpr_add); > diff --git a/drivers/dma-buf/heaps/tegra-vpr.c b/drivers/dma-buf/heaps/tegra-vpr.c > new file mode 100644 > index 000000000000..d8cff7e07ea0 > --- /dev/null > +++ b/drivers/dma-buf/heaps/tegra-vpr.c > @@ -0,0 +1,1210 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * DMA-BUF restricted heap exporter for NVIDIA Video-Protection-Region (VPR) > + * > + * Copyright (C) 2024-2026 NVIDIA Corporation > + */ > + > +#define pr_fmt(fmt) "tegra-vpr: " fmt > + > +#include <linux/arm-smccc.h> > +#include <linux/cma.h> > +#include <linux/debugfs.h> > +#include <linux/dma-buf.h> > +#include <linux/dma-heap.h> > +#include <linux/find.h> > +#include <linux/memory.h> > +#include <linux/of_reserved_mem.h> > +#include <linux/platform_device.h> > +#include <linux/pm_runtime.h> > +#include <linux/reset.h> > +#include <linux/set_memory.h> > + > +#include "tegra-vpr.h" > + > +MODULE_IMPORT_NS("DMA_BUF_HEAP"); > +MODULE_IMPORT_NS("DMA_BUF"); > + > +#define CREATE_TRACE_POINTS > +#include <trace/events/tegra_vpr.h> > + > +#define TEGRA_VPR_MAX_CHUNKS 64 > + > +struct tegra_vpr_buffer { > + struct list_head attachments; > + struct tegra_vpr *vpr; > + struct list_head list; > + > + /** > + * @lock: Protects concurrent access to the list of attachments. > + */ > + struct mutex lock; > + > + struct page **pages; > + pgoff_t num_pages; > + phys_addr_t start; > + phys_addr_t limit; > + size_t size; > + int pageno; > + int order; > + > + DECLARE_BITMAP(chunks, TEGRA_VPR_MAX_CHUNKS); > +}; > + > +struct tegra_vpr_attachment { > + struct device *dev; > + struct sg_table sgt; > + struct list_head list; > +}; > + > +#define ARM_SMCCC_TE_FUNC_PROGRAM_VPR 0x3 > + > +#define ARM_SMCCC_VENDOR_SIP_TE_PROGRAM_VPR_FUNC_ID \ > + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ > + ARM_SMCCC_SMC_32, \ > + ARM_SMCCC_OWNER_SIP, \ > + ARM_SMCCC_TE_FUNC_PROGRAM_VPR) > + > +static int tegra_vpr_set(phys_addr_t base, phys_addr_t size) > +{ > + struct arm_smccc_res res; > + > + arm_smccc_smc(ARM_SMCCC_VENDOR_SIP_TE_PROGRAM_VPR_FUNC_ID, base, size, > + 0, 0, 0, 0, 0, &res); > + > + return res.a0; > +} > + > +static int tegra_vpr_get_extents(struct tegra_vpr *vpr, phys_addr_t *base, > + phys_addr_t *size) > +{ > + phys_addr_t start = ~0, limit = 0; > + unsigned int i; > + > + for (i = 0; i < vpr->num_chunks; i++) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + if (chunk->active) { > + if (chunk->start < start) > + start = chunk->start; > + > + if (chunk->limit > limit) > + limit = chunk->limit; > + } > + } > + > + if (limit > start) { > + *size = limit - start; > + *base = start; > + } else { > + *base = *size = 0; > + } > + > + return 0; > +} > + > +static int tegra_vpr_resize(struct tegra_vpr *vpr) > +{ > + struct tegra_vpr_device *node; > + phys_addr_t base, size; > + int err, status = 0; > + > + err = tegra_vpr_get_extents(vpr, &base, &size); > + if (err < 0) { > + pr_err("%s(): failed to get VPR extents: %d\n", __func__, err); > + return err; > + } > + > + list_for_each_entry(node, &vpr->devices, node) { > + err = pm_generic_freeze(node->dev); > + if (err < 0) { > + pr_err("failed to freeze %s: %d\n", > + dev_name(node->dev), err); > + status = err; > + goto thaw; > + } > + } > + > + trace_tegra_vpr_set(base, size); > + > + err = tegra_vpr_set(base, size); > + if (err < 0) { > + pr_err("failed to secure VPR: %d\n", err); > + status = err; > + } > + > +thaw: > + list_for_each_entry_continue_reverse(node, &vpr->devices, node) { > + err = pm_generic_thaw(node->dev); > + if (err < 0) { > + pr_err("failed to thaw %s: %d\n", > + dev_name(node->dev), err); > + continue; > + } > + } > + > + return status; > +} > + > +static int tegra_vpr_chunk_init(struct tegra_vpr *vpr, > + struct tegra_vpr_chunk *chunk, > + phys_addr_t start, size_t size, > + unsigned int order, const char *name) > +{ > + chunk->start = start; > + chunk->limit = start + size; > + chunk->size = size; > + chunk->vpr = vpr; > + > + chunk->offset = (start - vpr->base) >> PAGE_SHIFT; > + chunk->num_pages = size >> PAGE_SHIFT; > + chunk->num_buffers = 0; > + > + /* CMA area is not reserved yet */ > + chunk->start_page = NULL; > + chunk->virt = 0; > + > + return 0; > +} > + > +static void tegra_vpr_chunk_free(struct tegra_vpr_chunk *chunk) > +{ > +} > + > +static inline bool tegra_vpr_chunk_is_last(const struct tegra_vpr_chunk *chunk) > +{ > + phys_addr_t limit = chunk->vpr->base + chunk->vpr->size; > + > + return chunk->limit == limit; > +} > + > +static inline bool tegra_vpr_chunk_is_leaf(const struct tegra_vpr_chunk *chunk) > +{ > + const struct tegra_vpr_chunk *next = chunk + 1; > + > + if (tegra_vpr_chunk_is_last(chunk)) > + return true; > + > + return !next->active; > +} > + > +static int tegra_vpr_chunk_alloc(struct tegra_vpr_chunk *chunk) > +{ > + chunk->start_page = cma_alloc_at(chunk->vpr->cma, chunk->offset, > + chunk->num_pages, false); > + if (!chunk->start_page) > + return -ENOMEM; > + > + chunk->virt = (unsigned long)page_to_virt(chunk->start_page); > + > + return 0; > +} > + > +static int tegra_vpr_chunk_activate(struct tegra_vpr_chunk *chunk) > +{ > + int err; > + > + trace_tegra_vpr_chunk_activate(chunk->start, chunk->limit); > + > + err = set_direct_map_invalid_noflush(chunk->start_page, > + chunk->num_pages); > + if (err) > + return err; > + > + flush_tlb_kernel_range(chunk->virt, chunk->virt + chunk->size); > + chunk->invalid = false; > + chunk->active = true; > + > + return 0; > +} > + > +static int tegra_vpr_chunk_deactivate(struct tegra_vpr_chunk *chunk) > +{ > + int err; > + > + if (!chunk->active) > + return 0; > + > + /* do not deactivate if there are buffers left in this chunk */ > + if (WARN_ON(chunk->num_buffers > 0)) > + return -EBUSY; > + > + trace_tegra_vpr_chunk_deactivate(chunk->start, chunk->limit); > + > + err = set_direct_map_default_noflush(chunk->start_page, > + chunk->num_pages); > + if (err) > + return err; > + > + flush_tlb_kernel_range(chunk->virt, chunk->virt + chunk->size); > + chunk->invalid = false; > + chunk->active = false; > + > + return 0; > +} > + > +static void tegra_vpr_chunk_release(struct tegra_vpr_chunk *chunk) > +{ > + if (!WARN_ON(chunk->active || chunk->invalid)) { > + cma_release(chunk->vpr->cma, chunk->start_page, > + chunk->num_pages); > + chunk->start_page = NULL; > + chunk->virt = 0; > + } > +} > + > +static bool tegra_vpr_chunk_overlaps(struct tegra_vpr_chunk *chunk, > + unsigned int start, unsigned int limit) > +{ > + unsigned int first = chunk->offset; > + unsigned int last = chunk->offset + chunk->num_pages - 1; > + > + if (last < start || first >= limit) > + return false; > + > + return true; > +} > + > +static int tegra_vpr_activate_chunks(struct tegra_vpr *vpr, > + struct tegra_vpr_buffer *buffer) > +{ > + DECLARE_BITMAP(dirty, vpr->num_chunks); > + unsigned int i, bottom, top; > + int err = 0, ret; > + > + bitmap_zero(dirty, vpr->num_chunks); > + > + /* activate any inactive chunks that overlap this buffer */ > + for_each_set_bit(i, buffer->chunks, vpr->num_chunks) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + if (chunk->active) > + continue; > + > + err = tegra_vpr_chunk_alloc(chunk); > + if (err < 0) > + goto deactivate; > + > + err = tegra_vpr_chunk_activate(chunk); > + if (err < 0) { > + tegra_vpr_chunk_release(chunk); > + goto deactivate; > + } > + > + set_bit(i, vpr->active); > + set_bit(i, dirty); > + } > + > + /* > + * Activating chunks above may have created holes, but since the VPR > + * can only ever be a single contiguous region, make sure to activate > + * any missing chunks. > + */ > + for_each_clear_bitrange(bottom, top, vpr->active, vpr->num_chunks) { > + /* inactive chunks at the bottom or the top are harmless */ > + if (bottom == 0 || top == vpr->num_chunks) > + continue; > + > + for (i = bottom; i < top; i++) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + err = tegra_vpr_chunk_alloc(chunk); > + if (err < 0) > + goto deactivate; > + > + err = tegra_vpr_chunk_activate(chunk); > + if (err < 0) { > + tegra_vpr_chunk_release(chunk); > + goto deactivate; > + } > + > + set_bit(i, vpr->active); > + set_bit(i, dirty); > + } > + } > + > + /* if any chunks have been activated, VPR needs to be resized */ > + if (!bitmap_empty(dirty, vpr->num_chunks)) { > + err = tegra_vpr_resize(vpr); > + if (err < 0) { > + pr_err("failed to grow VPR: %d\n", err); > + goto deactivate; > + } > + } > + > + /* increment buffer count for each chunk */ > + for_each_set_bit(i, buffer->chunks, vpr->num_chunks) > + vpr->chunks[i].num_buffers++; > + > + return 0; > + > +deactivate: > + /* deactivate any of the previously inactive chunks on failure */ > + for_each_set_bit(i, dirty, vpr->num_chunks) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + ret = tegra_vpr_chunk_deactivate(chunk); > + if (WARN_ON(ret < 0)) { > + pr_err("failed to deactivate chunk #%u: %d\n", i, ret); > + } else { > + tegra_vpr_chunk_release(chunk); > + clear_bit(i, vpr->active); > + } > + } > + > + return err; > +} > + > +/* > + * Retrieve the range of pages within the activate region of the VPR. > + */ > +static bool tegra_vpr_get_active_range(struct tegra_vpr *vpr, > + unsigned int *first, > + unsigned int *last) > +{ > + unsigned long i, j; > + > + i = find_first_bit(vpr->active, vpr->num_chunks); > + if (i >= vpr->num_chunks) > + return false; > + > + j = find_last_bit(vpr->active, vpr->num_chunks); > + if (j >= vpr->num_chunks) > + return false; > + > + *first = vpr->chunks[i].offset; > + *last = vpr->chunks[j].offset + vpr->chunks[j].num_pages; > + > + return true; > +} > + > +/* > + * Try to find and allocate a free region within a specific page range. > + * Returns the page number if successful, -ENOSPC otherwise. > + * > + * This function mimics bitmap_find_free_region() but restricts the search > + * to a specific range to enable allocation within individual chunks. > + */ > +static int tegra_vpr_find_free_region_in_range(struct tegra_vpr *vpr, > + unsigned int start_page, > + unsigned int end_page, > + unsigned int num_pages, > + unsigned int align) > +{ > + unsigned int pos, next = ALIGN(start_page, align); > + > + /* Scan through aligned positions, trying to allocate at each one */ > + for (pos = next; pos + num_pages <= end_page; pos = next) { > + next = find_next_bit(vpr->bitmap, pos + num_pages, pos); > + > + if (next >= pos + num_pages) { > + bitmap_set(vpr->bitmap, pos, num_pages); > + return pos; > + } > + > + next = find_next_zero_bit(vpr->bitmap, vpr->num_pages, next); > + next = ALIGN(next, align); > + } > + > + return -ENOSPC; > +} > + > +static int tegra_vpr_find_free_region(struct tegra_vpr *vpr, > + unsigned int num_pages, > + unsigned long align) > +{ > + return tegra_vpr_find_free_region_in_range(vpr, 0, vpr->num_pages - 1, > + num_pages, align); > +} > + > +static int tegra_vpr_find_free_region_clustered(struct tegra_vpr *vpr, > + unsigned int num_pages, > + unsigned int align) > +{ > + unsigned int target, first, last; > + int pageno; > + > + /* > + * If there are no allocations, abort the clustered allocation scheme > + * and use the generic allocation scheme instead. > + */ > + if (vpr->first > vpr->last) > + return -ENOSPC; > + > + /* > + * First, try to allocate within the currently allocated region. This > + * keeps allocations tightly packed and minimizes the VPR size needed. > + */ > + pageno = tegra_vpr_find_free_region_in_range(vpr, vpr->first, > + vpr->last + 1, num_pages, > + align); > + if (pageno >= 0) > + return pageno; > + > + /* > + * If not enough free space exists within the currently allocated > + * region, check to see if the allocation fits anywhere within the > + * active region, avoiding the need to resize the VPR. > + */ > + if (tegra_vpr_get_active_range(vpr, &first, &last)) { > + pageno = tegra_vpr_find_free_region_in_range(vpr, first, last, > + num_pages, align); > + if (pageno >= 0) > + return pageno; > + } > + > + /* > + * If not enough free space exists within the currently active region, > + * try to allocate adjacent to it to grow it contiguously and ensure > + * optimal packing. > + */ > + > + /* > + * Calculate where the allocation should start to end right at the > + * first allocated page, with proper alignment. > + */ > + if (vpr->first >= num_pages) { > + target = ALIGN_DOWN(vpr->first - num_pages, align); > + > + if (!bitmap_allocate(vpr->bitmap, target, num_pages)) > + return target; > + } > + > + /* Try after the last allocation */ > + target = ALIGN(vpr->last + 1, align); > + > + if (target + num_pages <= vpr->num_pages && > + !bitmap_allocate(vpr->bitmap, target, num_pages)) > + return target; > + > + /* > + * Couldn't allocate at the ideal adjacent position, search for any > + * available space before the first allocated page. > + */ > + pageno = tegra_vpr_find_free_region_in_range(vpr, 0, vpr->first, > + num_pages, align); > + if (pageno >= 0) > + return pageno; > + > + /* > + * Couldn't allocate at the ideal adjacent position, search > + * for any available space after the last allocated page. > + */ > + pageno = tegra_vpr_find_free_region_in_range(vpr, vpr->last + 1, > + vpr->num_pages, num_pages, > + align); > + if (pageno >= 0) > + return pageno; > + > + return -ENOSPC; > +} > + > +/* > + * Find a free region, preferring locations near existing allocations to > + * minimize VPR fragmentation. The allocation strategy is to first allocate > + * within or adjacent to the existing region to keep allocations clustered. > + * Otherwise fall back to a generic allocation using the first available > + * space. > + * > + * This approach focuses on page-level allocation first, then the chunk > + * system determines which chunks need to be activated based on where the > + * pages ended up. > + */ > +static int tegra_vpr_allocate_region(struct tegra_vpr *vpr, > + unsigned int num_pages, > + unsigned int align) > +{ > + int pageno; > + > + /* > + * For non-resizable VPR (no chunks), use simple first-fit allocation. > + * Clustering optimization is only beneficial for resizable VPR where > + * keeping allocations together minimizes the active VPR size. > + */ > + if (!vpr->resizable) > + return tegra_vpr_find_free_region(vpr, num_pages, align); > + > + /* > + * Check if there are any existing allocations in the bitmap. If so, > + * try to allocate near them to minimize fragmentation. > + */ > + pageno = tegra_vpr_find_free_region_clustered(vpr, num_pages, align); > + if (pageno >= 0) > + return pageno; > + > + /* > + * If there are no existing allocations, or no space adjacent to them, > + * fall back to the first available space anywhere in the VPR. > + */ > + pageno = tegra_vpr_find_free_region(vpr, num_pages, align); > + if (pageno >= 0) > + return pageno; > + > + return -ENOSPC; > +} > + > +static struct tegra_vpr_buffer * > +tegra_vpr_buffer_allocate(struct tegra_vpr *vpr, size_t size) > +{ > + unsigned int num_pages = size >> PAGE_SHIFT; > + unsigned int order = get_order(size); > + struct tegra_vpr_buffer *buffer; > + unsigned long first, last; > + int pageno, err; > + > + /* > + * Quick sanity check that we're not trying to allocate a buffer that > + * has no chance of fitting into the VPR. > + */ > + if (size > vpr->size) > + return ERR_PTR(-EINVAL); > + > + /* > + * "order" defines the alignment and size, so this may result in > + * fragmented memory depending on the allocation patterns. However, > + * since this is used primarily for video frames, it is expected that > + * a number of buffers of the same size will be allocated, so > + * fragmentation should be negligible. > + */ > + pageno = tegra_vpr_allocate_region(vpr, num_pages, 1); > + if (pageno < 0) > + return ERR_PTR(pageno); > + > + first = find_first_bit(vpr->bitmap, vpr->num_pages); > + last = find_last_bit(vpr->bitmap, vpr->num_pages); > + > + buffer = kzalloc_obj(*buffer, GFP_KERNEL); > + if (!buffer) { > + err = -ENOMEM; > + goto release; > + } > + > + INIT_LIST_HEAD(&buffer->attachments); > + INIT_LIST_HEAD(&buffer->list); > + mutex_init(&buffer->lock); > + buffer->start = vpr->base + (pageno << PAGE_SHIFT); > + buffer->limit = buffer->start + size; > + buffer->size = size; > + buffer->num_pages = num_pages; > + buffer->pageno = pageno; > + buffer->order = order; > + > + /* track which chunks this buffer overlaps */ > + if (vpr->resizable) { > + unsigned int limit = buffer->pageno + buffer->num_pages; > + pgoff_t i; > + > + /* > + * Memory is backed by struct page, so track which ones we > + * use. > + */ > + buffer->pages = kvmalloc_array(buffer->num_pages, > + sizeof(*buffer->pages), > + GFP_KERNEL); > + if (!buffer->pages) { > + err = -ENOMEM; > + goto free; > + } > + > + for (i = 0; i < buffer->num_pages; i++) > + buffer->pages[i] = &vpr->start_page[pageno + i]; > + > + for (i = 0; i < vpr->num_chunks; i++) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + if (tegra_vpr_chunk_overlaps(chunk, pageno, limit)) > + set_bit(i, buffer->chunks); > + } > + > + /* activate chunks if necessary */ > + err = tegra_vpr_activate_chunks(vpr, buffer); > + if (err < 0) { > + kfree(buffer->pages); > + goto free; > + } > + > + /* track first and last allocated pages */ > + if (buffer->pageno < vpr->first) > + vpr->first = buffer->pageno; > + > + if (limit - 1 > vpr->last) > + vpr->last = limit - 1; > + } > + > + return buffer; > + > +free: > + kfree(buffer); > +release: > + bitmap_clear(vpr->bitmap, pageno, num_pages); > + return ERR_PTR(err); > +} > + > +static void tegra_vpr_buffer_release(struct tegra_vpr_buffer *buffer) > +{ > + struct tegra_vpr *vpr = buffer->vpr; > + struct tegra_vpr_buffer *entry; > + unsigned int i; > + > + /* > + * Decrement buffer count for each overlapping chunk. Note that chunks > + * are not deactivated here yet, that's done in tegra_vpr_recycle() > + * instead. > + */ > + for_each_set_bit(i, buffer->chunks, vpr->num_chunks) { > + if (!WARN_ON(vpr->chunks[i].num_buffers == 0)) > + vpr->chunks[i].num_buffers--; > + } > + > + /* track first and last allocated pages */ > + if (list_is_first(&buffer->list, &vpr->buffers) && > + list_is_last(&buffer->list, &vpr->buffers)) { > + /* if there are no remaining buffers after this, reset */ > + vpr->first = ~0U; > + vpr->last = 0U; > + } else if (list_is_first(&buffer->list, &vpr->buffers)) { > + entry = list_next_entry(buffer, list); > + vpr->first = entry->pageno; > + } else if (list_is_last(&buffer->list, &vpr->buffers)) { > + entry = list_prev_entry(buffer, list); > + vpr->last = entry->pageno + entry->num_pages - 1; > + } > + > + bitmap_clear(vpr->bitmap, buffer->pageno, buffer->num_pages); > + list_del(&buffer->list); > + kfree(buffer->pages); > + kfree(buffer); > +} > + > +static int tegra_vpr_attach(struct dma_buf *buf, > + struct dma_buf_attachment *attachment) > +{ > + struct tegra_vpr_buffer *buffer = buf->priv; > + struct tegra_vpr_attachment *attach; > + int err; > + > + attach = kzalloc_obj(*attach, GFP_KERNEL); > + if (!attach) > + return -ENOMEM; > + > + /* > + * For resizable VPR, the memory is backed by struct page, so we can > + * use the convenient helper to create the SG table. > + */ > + if (buffer->pages) { > + err = sg_alloc_table_from_pages(&attach->sgt, buffer->pages, > + buffer->num_pages, 0, > + buffer->size, GFP_KERNEL); > + if (err < 0) > + goto free; > + } else { > + if (sg_alloc_table(&attach->sgt, 1, GFP_KERNEL)) { > + err = -ENOMEM; > + goto free; > + } > + > + sg_set_page(attach->sgt.sgl, NULL, buffer->size, 0); > + sg_dma_address(attach->sgt.sgl) = buffer->start; > + sg_dma_len(attach->sgt.sgl) = buffer->size; > + } > + > + attach->dev = attachment->dev; > + INIT_LIST_HEAD(&attach->list); > + attachment->priv = attach; > + > + mutex_lock(&buffer->lock); > + list_add(&attach->list, &buffer->attachments); > + mutex_unlock(&buffer->lock); > + > + return 0; > + > +free: > + kfree(attach); > + return err; > +} > + > +static void tegra_vpr_detach(struct dma_buf *buf, > + struct dma_buf_attachment *attachment) > +{ > + struct tegra_vpr_buffer *buffer = buf->priv; > + struct tegra_vpr_attachment *attach = attachment->priv; > + > + mutex_lock(&buffer->lock); > + list_del(&attach->list); > + mutex_unlock(&buffer->lock); > + > + sg_free_table(&attach->sgt); > + kfree(attach); > +} > + > +static struct sg_table * > +tegra_vpr_map_dma_buf(struct dma_buf_attachment *attachment, > + enum dma_data_direction direction) > +{ > + struct tegra_vpr_attachment *attach = attachment->priv; > + struct sg_table *sgt = &attach->sgt; > + int err; > + > + err = dma_map_sgtable(attachment->dev, sgt, direction, > + DMA_ATTR_SKIP_CPU_SYNC); > + if (err < 0) > + return ERR_PTR(err); > + > + return sgt; > +} > + > +static void tegra_vpr_unmap_dma_buf(struct dma_buf_attachment *attachment, > + struct sg_table *sgt, > + enum dma_data_direction direction) > +{ > + dma_unmap_sgtable(attachment->dev, sgt, direction, > + DMA_ATTR_SKIP_CPU_SYNC); > +} > + > +static void tegra_vpr_recycle(struct tegra_vpr *vpr) > +{ > + DECLARE_BITMAP(dirty, vpr->num_chunks); > + unsigned int i; > + int err; > + > + if (!vpr->resizable) > + return; > + > + bitmap_zero(dirty, vpr->num_chunks); > + > + /* > + * Deactivate any unused chunks from the bottom... > + */ > + for (i = 0; i < vpr->num_chunks; i++) { > + struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + if (!chunk->active) > + continue; > + > + if (chunk->num_buffers > 0) > + break; > + > + err = tegra_vpr_chunk_deactivate(chunk); > + if (err < 0) { > + pr_err("failed to deactivate chunk #%u: %d\n", i, err); > + goto activate; > + } else { > + clear_bit(i, vpr->active); > + set_bit(i, dirty); > + } > + } > + > + /* > + * ... and the top. > + */ > + for (i = 0; i < vpr->num_chunks; i++) { > + unsigned int index = vpr->num_chunks - i - 1; > + struct tegra_vpr_chunk *chunk = &vpr->chunks[index]; > + > + if (!chunk->active) > + continue; > + > + if (chunk->num_buffers > 0) > + break; > + > + err = tegra_vpr_chunk_deactivate(chunk); > + if (err < 0) { > + pr_err("failed to deactivate chunk #%u: %d\n", index, > + err); > + goto activate; > + } else { > + clear_bit(index, vpr->active); > + set_bit(index, dirty); > + } > + } > + > + if (!bitmap_empty(dirty, vpr->num_chunks)) { > + err = tegra_vpr_resize(vpr); > + if (err < 0) { > + pr_err("failed to shrink VPR: %d\n", err); > + goto activate; > + } > + } > + > + /* release the CMA memory associated with deactivated chunks */ > + for_each_set_bit(i, dirty, vpr->num_chunks) > + tegra_vpr_chunk_release(&vpr->chunks[i]); > + > + return; > + > +activate: > + for_each_set_bit(i, dirty, vpr->num_chunks) { > + err = tegra_vpr_chunk_activate(&vpr->chunks[i]); > + if (WARN_ON(err < 0)) > + pr_err("failed to activate chunk #%u: %d\n", i, err); > + > + /* > + * This may not be fully activated at this point, but we need > + * to keep track of it anyway to make sure the CMA region can > + * eventually be released. The WARN_ON above tells us when it > + * happens: here be dragons. > + */ > + set_bit(i, vpr->active); > + } > +} > + > +static void tegra_vpr_release(struct dma_buf *buf) > +{ > + struct tegra_vpr_buffer *buffer = buf->priv; > + struct tegra_vpr *vpr = buffer->vpr; > + > + mutex_lock(&vpr->lock); > + > + tegra_vpr_buffer_release(buffer); > + tegra_vpr_recycle(vpr); > + > + mutex_unlock(&vpr->lock); > +} > + > +/* > + * Prohibit userspace mapping because the CPU cannot access this memory > + * anyway. > + */ > +static int tegra_vpr_begin_cpu_access(struct dma_buf *buf, > + enum dma_data_direction direction) > +{ > + return -EPERM; > +} > + > +static int tegra_vpr_end_cpu_access(struct dma_buf *buf, > + enum dma_data_direction direction) > +{ > + return -EPERM; > +} > + > +static int tegra_vpr_mmap(struct dma_buf *buf, struct vm_area_struct *vma) > +{ > + return -EPERM; > +} > + > +static const struct dma_buf_ops tegra_vpr_buf_ops = { > + .attach = tegra_vpr_attach, > + .detach = tegra_vpr_detach, > + .map_dma_buf = tegra_vpr_map_dma_buf, > + .unmap_dma_buf = tegra_vpr_unmap_dma_buf, > + .release = tegra_vpr_release, > + .begin_cpu_access = tegra_vpr_begin_cpu_access, > + .end_cpu_access = tegra_vpr_end_cpu_access, > + .mmap = tegra_vpr_mmap, > +}; > + > +static struct dma_buf *tegra_vpr_allocate(struct dma_heap *heap, > + unsigned long len, u32 fd_flags, > + u64 heap_flags) > +{ > + struct tegra_vpr *vpr = dma_heap_get_drvdata(heap); > + struct tegra_vpr_buffer *buffer, *entry; > + size_t size = ALIGN(len, vpr->align); > + DEFINE_DMA_BUF_EXPORT_INFO(export); > + struct dma_buf *buf; > + > + mutex_lock(&vpr->lock); > + > + buffer = tegra_vpr_buffer_allocate(vpr, size); > + if (IS_ERR(buffer)) { > + mutex_unlock(&vpr->lock); > + return ERR_CAST(buffer); > + } > + > + /* insert in the correct order */ > + if (!list_empty(&vpr->buffers)) { > + list_for_each_entry(entry, &vpr->buffers, list) { > + if (buffer->pageno < entry->pageno) { > + list_add_tail(&buffer->list, &entry->list); > + break; > + } > + } > + } > + > + if (list_empty(&buffer->list)) > + list_add_tail(&buffer->list, &vpr->buffers); > + > + buffer->vpr = vpr; > + > + /* > + * If a valid buffer was allocated, wrap it in a dma_buf > + * and return it. > + */ > + export.exp_name = dma_heap_get_name(heap); > + export.ops = &tegra_vpr_buf_ops; > + export.size = buffer->size; > + export.flags = fd_flags; > + export.priv = buffer; > + > + buf = dma_buf_export(&export); > + if (IS_ERR(buf)) { > + tegra_vpr_buffer_release(buffer); > + tegra_vpr_recycle(vpr); > + } > + > + mutex_unlock(&vpr->lock); > + return buf; > +} > + > +static void tegra_vpr_debugfs_show_buffers(struct tegra_vpr *vpr, > + struct seq_file *s) > +{ > + struct tegra_vpr_buffer *buffer; > + char buf[16]; > + > + mutex_lock(&vpr->lock); > + > + list_for_each_entry(buffer, &vpr->buffers, list) { > + string_get_size(buffer->size, 1, STRING_UNITS_2, buf, > + sizeof(buf)); > + seq_printf(s, " %pap-%pap (%s)\n", &buffer->start, > + &buffer->limit, buf); > + } > + > + mutex_unlock(&vpr->lock); > +} > + > +static void tegra_vpr_debugfs_show_chunks(struct tegra_vpr *vpr, > + struct seq_file *s) > +{ > + struct tegra_vpr_buffer *buffer; > + unsigned int i; > + char buf[16]; > + > + for (i = 0; i < vpr->num_chunks; i++) { > + const struct tegra_vpr_chunk *chunk = &vpr->chunks[i]; > + > + string_get_size(chunk->size, 1, STRING_UNITS_2, buf, > + sizeof(buf)); > + seq_printf(s, " %pap-%pap (%s) (%s, %u buffers)\n", > + &chunk->start, &chunk->limit, buf, > + chunk->active ? "active" : "inactive", > + chunk->num_buffers); > + } > + > + list_for_each_entry(buffer, &vpr->buffers, list) { > + string_get_size(buffer->size, 1, STRING_UNITS_2, buf, > + sizeof(buf)); > + seq_printf(s, "%pap-%pap (%s, chunks: %*pbl)\n", > + &buffer->start, &buffer->limit, buf, > + vpr->num_chunks, buffer->chunks); > + } > +} > + > +static int tegra_vpr_debugfs_show(struct seq_file *s, struct dma_heap *heap) > +{ > + struct tegra_vpr *vpr = dma_heap_get_drvdata(heap); > + phys_addr_t limit = vpr->base + vpr->size; > + char buf[16]; > + > + string_get_size(vpr->size, 1, STRING_UNITS_2, buf, sizeof(buf)); > + seq_printf(s, "%pap-%pap (%s)\n", &vpr->base, &limit, buf); > + > + if (!vpr->resizable) > + tegra_vpr_debugfs_show_buffers(vpr, s); > + else > + tegra_vpr_debugfs_show_chunks(vpr, s); > + > + return 0; > +} > + > +static const struct dma_heap_ops tegra_vpr_heap_ops = { > + .allocate = tegra_vpr_allocate, > + .show = tegra_vpr_debugfs_show, > +}; > + > +static int tegra_vpr_setup_chunks(struct tegra_vpr *vpr, const char *name) > +{ > + phys_addr_t start, limit; > + unsigned int order, i = 0; > + size_t max_size; > + int err; > + > + /* Memory is backed by struct page, so track the first one. */ > + vpr->start_page = phys_to_page(vpr->base); > + > + /* This seems a reasonable value, so hard-code it for now. */ > + vpr->num_chunks = 4; > + > + vpr->chunks = kzalloc_objs(*vpr->chunks, vpr->num_chunks); > + if (!vpr->chunks) > + return -ENOMEM; > + > + vpr->active = bitmap_zalloc(vpr->num_chunks, GFP_KERNEL); > + if (!vpr->active) { > + err = -ENOMEM; > + goto free; > + } > + > + max_size = PAGE_SIZE << (get_order(vpr->size) - ilog2(vpr->num_chunks)); > + order = get_order(vpr->align); > + > + /* > + * Allocate CMA areas for VPR. All areas will be roughtly the same > + * size, with the last area taking up the rest. > + */ > + start = vpr->base; > + limit = vpr->base + vpr->size; > + > + pr_debug("VPR: %pap-%pap (%lu pages, %u chunks, %lu MiB)\n", &start, > + &limit, vpr->num_pages, vpr->num_chunks, > + (unsigned long)vpr->size / 1024 / 1024); > + > + for (i = 0; i < vpr->num_chunks; i++) { > + size_t size = limit - start; > + phys_addr_t end; > + > + size = min_t(size_t, size, max_size); > + end = start + size - 1; > + > + err = tegra_vpr_chunk_init(vpr, &vpr->chunks[i], start, size, > + order, name); > + if (err < 0) { > + pr_err("failed to create VPR chunk: %d\n", err); > + goto free; > + } > + > + pr_debug(" %2u: %pap-%pap (%lu MiB)\n", i, &start, &end, > + size / 1024 / 1024); > + start += size; > + } > + > + vpr->first = ~0U; > + vpr->last = 0U; > + > + return 0; > + > +free: > + while (i--) > + tegra_vpr_chunk_free(&vpr->chunks[i]); > + > + kfree(vpr->active); > + kfree(vpr->chunks); > + return err; > +} > + > +static void tegra_vpr_free_chunks(struct tegra_vpr *vpr) > +{ > + unsigned int i; > + > + for (i = 0; i < vpr->num_chunks; i++) > + tegra_vpr_chunk_free(&vpr->chunks[i]); > + > + kfree(vpr->chunks); > +} > + > +static int tegra_vpr_setup_static(struct tegra_vpr *vpr) > +{ > + phys_addr_t start, limit; > + > + start = vpr->base; > + limit = vpr->base + vpr->size; > + > + pr_debug("VPR: %pap-%pap (%lu pages, %lu MiB)\n", &start, &limit, > + vpr->num_pages, (unsigned long)vpr->size / 1024 / 1024); > + > + return 0; > +} > + > +static int tegra_vpr_add_heap(struct reserved_mem *rmem, > + struct device_node *np) > +{ > + struct dma_heap_export_info info = {}; > + unsigned long first, last; > + struct dma_heap *heap; > + struct tegra_vpr *vpr; > + int err; > + > + vpr = kzalloc_obj(*vpr, GFP_KERNEL); > + if (!vpr) > + return -ENOMEM; > + > + INIT_LIST_HEAD(&vpr->list); > + INIT_LIST_HEAD(&vpr->buffers); > + INIT_LIST_HEAD(&vpr->devices); > + mutex_init(&vpr->lock); > + > + vpr->resizable = !of_property_read_bool(np, "no-map"); > + vpr->dev_node = of_node_get(np); > + vpr->align = PAGE_SIZE; > + vpr->base = rmem->base; > + vpr->size = rmem->size; > + vpr->num_pages = vpr->size >> PAGE_SHIFT; > + vpr->nid = of_node_to_nid(np); If this gets used, I can't find it. Rob

1 week, 4 days

Re: [PATCH v6 07/12] mm/cma: Introduce cma_alloc_at() API

by Marek Szyprowski

On 04.09.2026 12:44, Thierry Reding wrote: > From: Thierry Reding <treding(a)nvidia.com> > > This API can be used to allocate a number of CMA pages starting at a > fixed offset. This is useful, for example, if the CMA area is used as > backing storage for a nested allocator that has stricter requirements > than CMA itself. > > In order to reuse most of the existing code, the cma_range_alloc() > function is enhanced to take as inputs a range of pages to look for a > free region. If this range encompasses the entire CMA range, the > behavior is as before, but the range can also be specified to match > the offset and size passed in from cma_alloc_at(), in which case that > is the range that will be allocated (or allocation will fail if the > range is not available). > > Suggested-by: Marek Szyprowski <m.szyprowski(a)samsung.com> > Signed-off-by: Thierry Reding <treding(a)nvidia.com> Acked-by: Marek Szyprowski <m.szyprowski(a)samsung.com> > --- > Changes in v6: > - refactor cma_range_alloc() so it can be reused for _at() code paths > --- > include/linux/cma.h | 4 +++ > include/trace/events/cma.h | 77 ++++++++++++++++++++++++++++++++++++++-- > mm/cma.c | 88 +++++++++++++++++++++++++++++++++++----------- > 3 files changed, 146 insertions(+), 23 deletions(-) > > diff --git a/include/linux/cma.h b/include/linux/cma.h > index 8555d38a97b1..844404459a42 100644 > --- a/include/linux/cma.h > +++ b/include/linux/cma.h > @@ -49,11 +49,15 @@ extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size, > struct cma **res_cma); > extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align, > bool no_warn); > +extern struct page *cma_alloc_at(struct cma *cma, unsigned long offset, > + unsigned long count, bool no_warn); > extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long count); > > struct page *cma_alloc_frozen(struct cma *cma, unsigned long count, > unsigned int align, bool no_warn); > struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order); > +struct page *cma_alloc_at_frozen(struct cma *cma, unsigned long offset, > + unsigned long count, bool no_warn); > bool cma_release_frozen(struct cma *cma, const struct page *pages, > unsigned long count); > > diff --git a/include/trace/events/cma.h b/include/trace/events/cma.h > index 37195edf2498..4e0ab63e303f 100644 > --- a/include/trace/events/cma.h > +++ b/include/trace/events/cma.h > @@ -38,13 +38,17 @@ TRACE_EVENT(cma_release, > > TRACE_EVENT(cma_alloc_start, > > - TP_PROTO(const char *name, unsigned long request_count, unsigned long available_count, > + TP_PROTO(const char *name, unsigned long start, unsigned long end, > + unsigned long request_count, unsigned long available_count, > unsigned long total_count, unsigned int align), > > - TP_ARGS(name, request_count, available_count, total_count, align), > + TP_ARGS(name, start, end, request_count, available_count, total_count, > + align), > > TP_STRUCT__entry( > __string(name, name) > + __field(unsigned long, start) > + __field(unsigned long, end) > __field(unsigned long, request_count) > __field(unsigned long, available_count) > __field(unsigned long, total_count) > @@ -53,14 +57,18 @@ TRACE_EVENT(cma_alloc_start, > > TP_fast_assign( > __assign_str(name); > + __entry->start = start; > + __entry->end = end; > __entry->request_count = request_count; > __entry->available_count = available_count; > __entry->total_count = total_count; > __entry->align = align; > ), > > - TP_printk("name=%s request_count=%lu available_count=%lu total_count=%lu align=%u", > + TP_printk("name=%s start=%lu end=%lu request_count=%lu available_count=%lu total_count=%lu align=%u", > __get_str(name), > + __entry->start, > + __entry->end, > __entry->request_count, > __entry->available_count, > __entry->total_count, > @@ -132,6 +140,69 @@ TRACE_EVENT(cma_alloc_busy_retry, > __entry->align) > ); > > +TRACE_EVENT(cma_alloc_at_start, > + > + TP_PROTO(const char *name, unsigned long pfn, > + unsigned long request_count, unsigned long available_count, > + unsigned long total_count), > + > + TP_ARGS(name, pfn, request_count, available_count, total_count), > + > + TP_STRUCT__entry( > + __string(name, name) > + __field(unsigned long, pfn) > + __field(unsigned long, request_count) > + __field(unsigned long, available_count) > + __field(unsigned long, total_count) > + ), > + > + TP_fast_assign( > + __assign_str(name); > + __entry->pfn = pfn; > + __entry->request_count = request_count; > + __entry->available_count = available_count; > + __entry->total_count = total_count; > + ), > + > + TP_printk("name=%s pfn=%lx, request_count=%lu available_count=%lu total_count=%lu", > + __get_str(name), > + __entry->pfn, > + __entry->request_count, > + __entry->available_count, > + __entry->total_count) > +); > + > +TRACE_EVENT(cma_alloc_at_finish, > + > + TP_PROTO(const char *name, unsigned long pfn, const struct page *page, > + unsigned long count, int errorno), > + > + TP_ARGS(name, pfn, page, count, errorno), > + > + TP_STRUCT__entry( > + __string(name, name) > + __field(unsigned long, pfn) > + __field(const struct page *, page) > + __field(unsigned long, count) > + __field(int, errorno) > + ), > + > + TP_fast_assign( > + __assign_str(name); > + __entry->pfn = pfn; > + __entry->page = page; > + __entry->count = count; > + __entry->errorno = errorno; > + ), > + > + TP_printk("name=%s pfn=0x%lx page=%p count=%lu errorno=%d", > + __get_str(name), > + __entry->pfn, > + __entry->page, > + __entry->count, > + __entry->errorno) > +); > + > #endif /* _TRACE_CMA_H */ > > /* This part must be outside protection */ > diff --git a/mm/cma.c b/mm/cma.c > index a10ea37a261d..f92d3a188209 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -783,25 +783,32 @@ static void cma_debug_show_areas(struct cma *cma) > spin_unlock_irq(&cma->lock); > } > > +/* > + * Searches the CMA memrange, from @start to @end, for a free region of > + * @count bits. If @end is less or equal to @start, will search the entire > + * memrange. > + */ > static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > - unsigned long count, unsigned int align, > - struct page **pagep, gfp_t gfp) > + unsigned long start, unsigned long end, > + unsigned long count, unsigned int align, > + struct page **pagep, gfp_t gfp) > { > unsigned long bitmap_maxno, bitmap_no, bitmap_count; > - unsigned long start, pfn, mask, offset; > - int ret = -EBUSY; > + unsigned long pfn, mask, offset; > struct page *page = NULL; > + int ret = -EBUSY; > > mask = cma_bitmap_aligned_mask(cma, align); > offset = cma_bitmap_aligned_offset(cma, cmr, align); > - bitmap_maxno = cma_bitmap_maxno(cma, cmr); > + bitmap_maxno = (end > start) ? end : cma_bitmap_maxno(cma, cmr); > bitmap_count = cma_bitmap_pages_to_bits(cma, count); > > if (bitmap_count > bitmap_maxno) > goto out; > > - for (start = 0; ; start = bitmap_no + mask + 1) { > + while (true) { > spin_lock_irq(&cma->lock); > + > /* > * If the request is larger than the available number > * of pages, stop right away. > @@ -810,6 +817,7 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > spin_unlock_irq(&cma->lock); > break; > } > + > bitmap_no = bitmap_find_next_zero_area_off(cmr->bitmap, > bitmap_maxno, start, bitmap_count, mask, > offset); > @@ -835,10 +843,11 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > > bitmap_set(cmr->bitmap, bitmap_no, bitmap_count); > cma->available_count -= count; > + > /* > - * It's safe to drop the lock here. We've marked this region for > - * our exclusive use. If the migration fails we will take the > - * lock again and unmark it. > + * It's safe to drop the lock here. We've marked this region > + * for our exclusive use. If the migration fails we will take > + * the lock again and unmark it. > */ > spin_unlock_irq(&cma->lock); > > @@ -856,37 +865,45 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > __func__, pfn, page); > > trace_cma_alloc_busy_retry(cma->name, pfn, page, count, align); > + start = bitmap_no + mask + 1; > } > + > out: > if (!ret) > *pagep = page; > + > return ret; > } > > -static struct page *__cma_alloc_frozen(struct cma *cma, > - unsigned long count, unsigned int align, gfp_t gfp) > +static struct page *__cma_alloc_frozen(struct cma *cma, unsigned long start, > + unsigned long end, unsigned long count, > + unsigned int align, gfp_t gfp) > { > struct page *page = NULL; > int ret = -ENOMEM, r; > unsigned long i; > - const char *name = cma ? cma->name : NULL; > + > + /* cma_alloc_at() and friends will only work with single-range CMA */ > + if (WARN_ON_ONCE(start > 0 && cma->nranges != 1)) > + return page; > > if (!cma || !cma->count) > return page; > > - pr_debug("%s(cma %p, name: %s, count %lu, align %d)\n", __func__, > - (void *)cma, cma->name, count, align); > + pr_debug("%s(cma %p, name: %s, start %lu, end %lu, count %lu, align %d)\n", > + __func__, (void *)cma, cma->name, start, end, count, align); > > if (!count) > return page; > > - trace_cma_alloc_start(name, count, cma->available_count, cma->count, align); > + trace_cma_alloc_start(cma->name, start, end, count, > + cma->available_count, cma->count, align); > > for (r = 0; r < cma->nranges; r++) { > page = NULL; > > - ret = cma_range_alloc(cma, &cma->ranges[r], count, align, > - &page, gfp); > + ret = cma_range_alloc(cma, &cma->ranges[r], start, end, > + count, align, &page, gfp); > if (ret != -EBUSY || page) > break; > } > @@ -908,7 +925,7 @@ static struct page *__cma_alloc_frozen(struct cma *cma, > } > > pr_debug("%s(): returned %p\n", __func__, page); > - trace_cma_alloc_finish(name, page ? page_to_pfn(page) : 0, > + trace_cma_alloc_finish(cma->name, page ? page_to_pfn(page) : 0, > page, count, align, ret); > if (page) { > count_vm_event(CMA_ALLOC_SUCCESS); > @@ -926,14 +943,22 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count, > { > gfp_t gfp = GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0); > > - return __cma_alloc_frozen(cma, count, align, gfp); > + return __cma_alloc_frozen(cma, 0, 0, count, align, gfp); > } > > struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order) > { > gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN; > > - return __cma_alloc_frozen(cma, 1 << order, order, gfp); > + return __cma_alloc_frozen(cma, 0, 0, 1 << order, order, gfp); > +} > + > +struct page *cma_alloc_at_frozen(struct cma *cma, unsigned long offset, > + unsigned long count, bool no_warn) > +{ > + gfp_t gfp = GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0); > + > + return __cma_alloc_frozen(cma, offset, offset + count, count, 0, gfp); > } > > /** > @@ -959,6 +984,29 @@ struct page *cma_alloc(struct cma *cma, unsigned long count, > } > EXPORT_SYMBOL_GPL(cma_alloc); > > +/** > + * cma_alloc_at() - allocate pages from contiguous area at fixed offset > + * @cma: Contiguous memory region for which the allocation is performed. > + * @offset: Index of the first page to allocate. > + * @count: Requested number of pages (in PAGE_SIZE order). > + * @no_warn: Avoid printing message about failed allocation. > + * > + * This function allocates a part of the contiguous memory on a specific > + * contiguous memory area. > + */ > +struct page *cma_alloc_at(struct cma *cma, unsigned long offset, > + unsigned long count, bool no_warn) > +{ > + struct page *page; > + > + page = cma_alloc_at_frozen(cma, offset, count, no_warn); > + if (page) > + set_pages_refcounted(page, count); > + > + return page; > +} > +EXPORT_SYMBOL_GPL(cma_alloc_at); > + > static struct cma_memrange *find_cma_memrange(struct cma *cma, > const struct page *pages, unsigned long count) > { > Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland

1 week, 4 days

[PATCH v2] dma-buf: Document how exporters and importers agree on mapping lifetime

by Leon Romanovsky

From: Leon Romanovsky <leonro(a)nvidia.com> Nothing in DMA-buf declares whether a mapping may be moved or taken away. Nearly every callback on both sides is optional, so the answer follows from which ones are implemented and from whether dma_buf_pin() succeeds. Documentation/ says none of this, and the rules sit in the kdoc of dma_buf_ops.pin, dma_buf_attach_ops.invalidate_mappings and dma_buf_invalidate_mappings(), which a driver author has to know by name before finding them. Describe the three flows an importer has to handle, the callbacks each one asks of both sides, and dma_buf_pin() as the runtime negotiation. Signed-off-by: Leon Romanovsky <leonro(a)nvidia.com> --- Let's try this variant from importer POV. Thanks Changes in v2: - Split pci p2p documentation patch to separate series - Improved dma-buf documentation patch. - Link to v1: https://patch.msgid.link/20260825-document-dma-buf-v1-0-5ecfb3e1371c@nvidia… --- Documentation/driver-api/dma-buf.rst | 6 ++++ drivers/dma-buf/dma-buf.c | 69 +++++++++++++++++++++++++++++++++++- 2 files changed, 74 insertions(+), 1 deletion(-) diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index 2f36c21d9948..39c201f38aa6 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -113,6 +113,12 @@ Basic Operation and Device DMA Access .. kernel-doc:: drivers/dma-buf/dma-buf.c :doc: dma buf device access +Mapping Lifetime Negotiation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: drivers/dma-buf/dma-buf.c + :doc: mapping lifetime negotiation + CPU Access to DMA Buffer Objects ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index d504c636dc29..aa47142cd9ed 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -684,7 +684,74 @@ static struct file *dma_buf_getfile(size_t size, int flags) * reference acquired with dma_buf_get() by calling dma_buf_put(). * * For the detailed semantics exporters are expected to implement see - * &dma_buf_ops. + * &dma_buf_ops. Whether the exporter may still move or take away the backing + * storage after step 3 depends on what both sides implement. See the mapping + * lifetime negotiation section below. + */ + +/** + * DOC: mapping lifetime negotiation + * + * Nearly everything in DMA-buf is optional. No flag or enum says whether the + * exporter may move or take away the backing storage while an importer holds + * a mapping. Each side simply implements the callbacks it can offer, and + * dma_buf_pin() settles the result at runtime. + * + * Out of that optionality the importer sees three main flows. They are named + * from the importer's point of view, because each one demands a different + * capability of its hardware: + * + * - Pinned: the memory is never taken away. The importer offers no way + * to stop DMA. + * - Revoked: the storage never moves, but the exporter may take it away. The + * importer must be able to stop DMA, and may hit user visible errors while + * doing so. + * - Movable: the exporter may relocate the storage at any time. The importer + * must be able to pause DMA, and must raise no error while the storage is + * moving. + * + * An importer reaches its flow like this: + * + * 1. Attach with dma_buf_dynamic_attach(). Leaving out the optional + * &dma_buf_attach_ops.invalidate_mappings callback pins the buffer for as + * long as the attachment exists. + * 2. Call dma_buf_pin() under the reservation lock. + * 3. On failure, run the movable flow or give up. + * 4. On success, the flow is the revoked one if the optional + * &dma_buf_attach_ops.invalidate_mappings is implemented, and the pinned + * one if it is not. + * + * Pinned flow: + * + * - Exporter: implement &dma_buf_ops.pin and &dma_buf_ops.unpin to hold the + * storage still on request. An exporter whose storage never moves implements + * neither, and dma_buf_pin() then succeeds on its own. An exporter which + * refuses to be pinned implements &dma_buf_ops.pin and fails it. + * - Importer: nothing more. The mapping stays valid until the importer unmaps. + * + * Revoked flow: + * + * - Exporter: answer dma_buf_pin() as above. Call + * dma_buf_invalidate_mappings() when the storage goes away and fail + * &dma_buf_ops.map_dma_buf while it is gone. The two waits which complete a + * revocation are described in dma_buf_invalidate_mappings(). + * - Importer: &dma_buf_attach_ops.invalidate_mappings has to unmap within + * bounded time and drop the pin. + * + * Movable flow: + * + * - Exporter: call dma_buf_invalidate_mappings() before each move, then wait + * for the &dma_buf.resv fences. &dma_buf_ops.pin and &dma_buf_ops.unpin play + * no part here. + * - Importer: hold no pin. &dma_buf_attach_ops.invalidate_mappings drops the + * cached mapping and has to lead to dma_buf_unmap_attachment() within + * bounded time. It need not stop the hardware, because access runs until the + * importer's &dma_buf.resv fences retire. The importer maps again before the + * next DMA. + * + * &dma_buf_ops.attach is the best place for an exporter to turn an importer + * away, because the importer can still fall back to another flow and attach + * again. */ /** --- base-commit: 63367df6e7255067ad6a83abe0d2799dfa491876 change-id: 20260820-document-dma-buf-3f8b41e32f57 Best regards, -- Leon Romanovsky <leonro(a)nvidia.com>

1 week, 6 days

[PATCH 0/2] Document the DMA-buf mapping lifetime negotiation

by Leon Romanovsky

DMA-buf lets an exporter pin, move or revoke the backing storage under an importer, and which of the three applies is decided by the optional callbacks each side implements and by whether dma_buf_pin() succeeds. Nothing in Documentation/ describes that, and the single reference to the mechanism still names move_notify(), removed in v7.1. Thanks Signed-off-by: Leon Romanovsky <leonro(a)nvidia.com> --- Leon Romanovsky (2): PCI/P2PDMA: Update DMABUF lifecycle docs after move_notify() rename dma-buf: Document how exporters and importers agree on mapping lifetime Documentation/driver-api/dma-buf.rst | 6 +++ Documentation/driver-api/pci/p2pdma.rst | 6 ++- drivers/dma-buf/dma-buf.c | 85 ++++++++++++++++++++++++++++++++- 3 files changed, 94 insertions(+), 3 deletions(-) --- base-commit: 8049741ac93acd3a590dac070e12571fddf0e294 change-id: 20260820-document-dma-buf-3f8b41e32f57 Best regards, -- Leon Romanovsky <leonro(a)nvidia.com>

2 weeks, 1 day

Re: [PATCH] Documentation/gpu: Fix brackets

by Randy Dunlap

Hi, On 9/3/26 9:10 AM, Manuel Ebner wrote: > Remove needless '(' and add missing ')'. > > Signed-off-by: Manuel Ebner <manuelebnerli(a)mailbox.org> > --- > Documentation/gpu/drm-vm-bind-locking.rst | 2 +- > Documentation/gpu/nova/core/todo.rst | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) This patch probably should be 2 patches since these files have different maintainers. > diff --git a/Documentation/gpu/drm-vm-bind-locking.rst b/Documentation/gpu/drm-vm-bind-locking.rst > index a345aa513..df6cf0132 100644 > --- a/Documentation/gpu/drm-vm-bind-locking.rst > +++ b/Documentation/gpu/drm-vm-bind-locking.rst > @@ -170,7 +170,7 @@ submission is therefore preceded with a re-validation section: > validate_gem_bo(&gpu_vm_bo->gem_bo); > > // The following list iteration needs the Gem object's > - // dma_resv to be held (it protects the gpu_vm_bo's list of > + // dma_resv to be held. It protects the gpu_vm_bo's list of > // gpu_vmas, but since local gem objects share the gpu_vm's > // dma_resv, it is already held at this point. I think that I must like parenthetical phrases more than you do. ;) Acked-by: Randy Dunlap <rdunlap(a)infradead.org> Thanks. > for_each_gpu_vma_of_gpu_vm_bo(&gpu_vm_bo, &gpu_vma) > diff --git a/Documentation/gpu/nova/core/todo.rst b/Documentation/gpu/nova/core/todo.rst > index d5130b2b0..a01c362b1 100644 > --- a/Documentation/gpu/nova/core/todo.rst > +++ b/Documentation/gpu/nova/core/todo.rst > @@ -33,7 +33,7 @@ A good example from nova-core would be the ``Chipset`` enum type, which defines > the value ``AD102``. When probing the GPU the value ``0x192`` can be read from a > certain register indication the chipset AD102. Hence, the enum value ``AD102`` > should be derived from the number ``0x192``. Currently, nova-core uses a custom > -implementation (``Chipset::from_u32`` for this. > +implementation (``Chipset::from_u32``) for this. > > Instead, it would be desirable to have something like the ``FromPrimitive`` > trait [1] from the num crate. -- ~Randy

2 weeks, 2 days

Re: [PATCH v8 2/2] dma-buf: Split sgl by largest page-aligned chunk

by Jason Gunthorpe

On Wed, Sep 02, 2026 at 07:07:50PM -0400, David Hu wrote: > On Wed, Sep 2, 2026 at 8:08 AM Jason Gunthorpe <jgg(a)ziepe.ca> wrote: > > > > On Tue, Sep 01, 2026 at 05:08:49PM +0000, David Hu wrote: > > > From: David Hu <xuehaohu(a)google.com> > > > > > > Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`. > > > This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the > > > first entry, resulting in non-page-aligned DMA addresses for all > > > subsequent entries. > > > > This patch is fine, but pedenatically a scatterlist's entry limit > > should be bounded to dma_get_max_seg_size(), though I don't think it > > helps this. Operating scatterlists at the size limits has proven > > problematic in a number of places already... > > > > > In addition, a non-page-aligned sgl length will trigger an edge case > > > in `ib_umem_find_best_pgsz()`. In case of a discontinuity in later > > > buffers, we will have a `va` with lowest bit set to 1. That will lead > > > to `ib_umem_find_best_pgsz()` always return 0, and break the promise > > > to find best page size for the mapping on the NIC side. > > > > That's an IB side bug, the newer logic that joins adjacent SGLs should > > have avoided it? > > Hi Jason, > > Thank you for the review. I think you are right on both counts. > Regarding the IB side, the new SGL joining logic in > `ib_umem_find_best_pgsz()` indeed avoids the issue. `mask |= va` is > skipped for artifically split, contiguous SGLs. Since Christian has > already pulled v8 into drm-misc-next, I won't spin a v9 to avoid > creating unnecessary noise on the list. If you prefer a followup, > please let me know. Nope, I'm fine, it just explains why it wasn't seen in other tested. You were backporting and mix&matched things. It confirms the upstream kernel was fine from the start. There are other importers besides RDMA, so I still think that this is a good change regardless. Having each segment remain page aligned, and staying away from ULONG_MAX that might trigger overflows is a friendly and robust thing to do for less sophisticated importers. Jason

2 weeks, 2 days

Re: [PATCH v8 0/2] dma-buf: Fix silent overflow and alignment

by Christian König

On 9/1/26 19:08, David Hu wrote: > From: David Hu <xuehaohu(a)google.com> > > This series address two related issues in scatter-gather mapping, > specifically for the MMIO based dma-buf mapping. The fixes ensure > sgt mapping is correct, and proper for large MMIO regions. > > Patch 1 fixes a silent integer overflow for mapping length exceeding 4G > (Previously submitted as [PATCH v7] dma-buf: Fix silent overflow for > phys vec to sgt) > https://lore.kernel.org/all/20260609164047.486227-1-xuehaohu@google.com/ > > Patch 2 Splits sgl by largest page aligned chunk > (Previously submitted as [PATCH v3] dma-buf: Split sgl by largest page-aligned chunk) > https://lore.kernel.org/all/20260722233806.3922093-1-dhu@x6u.co/ *sigh* such issues are exactly the reason why I didn't wanted the dma-mapping stuff inside DMA-buf. That clearly doesn't belong here. I'm going to push those fixes to drm-misc-next now, but when there are more issues like that will mark the code as abandoned and not maintained. Regards, Christian. > > Changes in v8: > - Combined the two patches into one unified series to avoid merge > conflicts. > - Collected Reviewed-by tag from Leon Romanovsky for Patch 2. > > David Hu (2): > dma-buf: Fix silent overflow for phys vec to sgt > dma-buf: Split sgl by largest page-aligned chunk > > drivers/dma-buf/dma-buf-mapping.c | 31 +++++++++++++++++++++---------- > 1 file changed, 21 insertions(+), 10 deletions(-) > > -- > 2.55.0.897.gb25b4bd76c-goog >

2 weeks, 3 days

Re: [PATCH v5 4/5] accel/amdxdna: refuse to flush an imported BO

by Lizhi Hou

Applied this to drm-misc-fixes. On 8/19/26 15:44, Taimuraz Kaitmazov wrote: > SYNC_BO clflushes an imported BO's scatterlist. An importer may not do > that: the memory belongs to the exporter, and dma-buf gives the importer > no interface to ask for maintenance on it. Refuse the request instead. > > is_import_bo() is (obj)->attach, which covers more than foreign buffers. > A userptr BO arrives through a ubuf, and on a carveout device every share > BO and the device heap arrive through a cbuf, so SYNC_BO answers > -EOPNOTSUPP for those too, including the AMDXDNA_BO_DEV path that flushes > through its heap. > > Only the ubuf case gives up maintenance it was getting: on a 64 MiB > userptr BO a 4 KiB sync and a full sync both cost 659 us, this arm having > ignored the range. amdxdna_cbuf_map() fills in only the DMA address and > length, so drm_clflush_sg() already walks zero pages on carveout memory. > Userspace maintains these through the mapping it already holds, as XRT's > buffer::sync() does unless it is told to sync through the driver. > > Suggested-by: Lizhi Hou <lizhi.hou(a)amd.com> > Signed-off-by: Taimuraz Kaitmazov <taimuraz(a)kaitmazov.com> > Reviewed-by: Lizhi Hou <lizhi.hou(a)amd.com> > --- > drivers/accel/amdxdna/amdxdna_gem.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c > index 0e0f844526ca..4be5298d1062 100644 > --- a/drivers/accel/amdxdna/amdxdna_gem.c > +++ b/drivers/accel/amdxdna/amdxdna_gem.c > @@ -1224,6 +1224,9 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size) > { > u64 end; > > + if (is_import_bo(abo)) > + return -EOPNOTSUPP; > + > if (offset >= abo->mem.size) > return -EINVAL; > > @@ -1234,9 +1237,7 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size) > if (!size) > return 0; > > - if (is_import_bo(abo)) > - drm_clflush_sg(abo->base.sgt); > - else if (amdxdna_gem_vmap(abo)) > + if (amdxdna_gem_vmap(abo)) > drm_clflush_virt_range(amdxdna_gem_vmap(abo) + offset, size); > else if (abo->base.pages) > drm_clflush_pages(abo->base.pages, abo->mem.size >> PAGE_SHIFT);

2 weeks, 3 days

Re: [PATCH v8 2/2] dma-buf: Split sgl by largest page-aligned chunk

by Jason Gunthorpe

On Tue, Sep 01, 2026 at 05:08:49PM +0000, David Hu wrote: > From: David Hu <xuehaohu(a)google.com> > > Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`. > This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the > first entry, resulting in non-page-aligned DMA addresses for all > subsequent entries. This patch is fine, but pedenatically a scatterlist's entry limit should be bounded to dma_get_max_seg_size(), though I don't think it helps this. Operating scatterlists at the size limits has proven problematic in a number of places already... > In addition, a non-page-aligned sgl length will trigger an edge case > in `ib_umem_find_best_pgsz()`. In case of a discontinuity in later > buffers, we will have a `va` with lowest bit set to 1. That will lead > to `ib_umem_find_best_pgsz()` always return 0, and break the promise > to find best page size for the mapping on the NIC side. That's an IB side bug, the newer logic that joins adjacent SGLs should have avoided it? Jason

2 weeks, 3 days

Re: [PATCH v4 1/2] drm: Add common drm_user_fence helper

by Christian König

On 8/28/26 10:31, SHANMUGAM, SRINIVASAN wrote: > AMD General > >> -----Original Message----- >> From: Koenig, Christian <Christian.Koenig(a)amd.com> >> Sent: Friday, August 28, 2026 1:48 PM >> To: SHANMUGAM, SRINIVASAN <SRINIVASAN.SHANMUGAM(a)amd.com>; >> Matthew Brost <matthew.brost(a)intel.com> >> Cc: Deucher, Alexander <Alexander.Deucher(a)amd.com>; Maarten Lankhorst >> <maarten.lankhorst(a)linux.intel.com>; Maxime Ripard <mripard(a)kernel.org>; >> Thomas Zimmermann <tzimmermann(a)suse.de>; David Airlie >> <airlied(a)gmail.com>; Simona Vetter <simona(a)ffwll.ch>; Sumit Semwal >> <sumit.semwal(a)linaro.org>; Thomas Hellström >> <thomas.hellstrom(a)linux.intel.com>; dri-devel(a)lists.freedesktop.org; intel- >> xe(a)lists.freedesktop.org; linux-media(a)vger.kernel.org; linaro-mm- >> sig(a)lists.linaro.org; linux-kernel(a)vger.kernel.org; amd-gfx(a)lists.freedesktop.org >> Subject: Re: [PATCH v4 1/2] drm: Add common drm_user_fence helper >> >> On 8/28/26 10:06, SHANMUGAM, SRINIVASAN wrote: >> ... >>>>> +/** >>>>> + * struct drm_user_fence - embeddable DRM user fence >>>>> + * >>>>> + * Drivers embed this in their own structure and implement >>>>> + * &drm_user_fence_ops. Call drm_user_fence_init() at creation and >>>>> + * drm_user_fence_add_callback() to arm on a dma-fence. >>>>> + * Call drm_user_fence_cancel_sync() before driver teardown. >>>>> + */ >>>>> +struct drm_user_fence { >>>> >>>> Should this common layer be split into two distinct concepts? >>>> >>>> - drm_work_fence: 90% of what is here, minus the kthread_use_mm() and >>>> mm-related code. >>>> - drm_user_fence: a subclass of drm_work_fence that adds the >>>> kthread_use_mm() and mm-related code. >>>> >>>> I suggest this because I was thinking about it the other day (I >>>> forget the exact >>>> context) and reconsidered a pattern where a fence signals and then I >>>> need a worker because some work must be done outside of IRQ context. >>>> A user fence is one example, since copy_to_user() can fault, which is >>>> not allowed in IRQ context. At various times in Xe we've had multiple >>>> patterns like this, although at the moment user fences are probably >>>> the only case that requires it. If we looked across DRM as a whole, I suspect >> we'd find this pattern open-coded in a number of places. >>>> >>>> Yes, drm_user_fence would be a very thin layer on top of >>>> drm_work_fence, but I still see value in the split. >>> >>> Hi Matt, >>> >>> Thanks for the review and for being supportive of the idea. >>> >>> The split into drm_work_fence (general fence-to-workqueue pattern) and >>> drm_user_fence (subclass adding kthread_use_mm) makes sense. I'll >>> restructure v5 as follows: >>> >>> drm_work_fence: kref, work_struct, dma_fence_cb, stored fence ref, >>> wq, ops — add_callback, cancel, cancel_sync >> >> Yeah, this pattern came up so often that I already considered adding it to the core >> dma_fence framework. > > Hi Christian, > > Thanks for the feedback. > > On dma_fence_work: would you prefer I place the generic fence-to-work > helper directly in the core dma_fence framework (drivers/dma-buf/), > or is starting with drm_work_fence in DRM and promoting it later also > acceptable? Maybe ask AI to search for use cases. If you find something outside of drivers/gpu/drm then please place it under drivers/dma-buf. If you don't find any existing use case drivers/gpu/drm should do as well. Thanks, Christian. > > I'll add the value comparison logic and will add a clear note that this cannot be > used to implement dma_fence_ops. > > Thanks, > Srini

3 weeks, 1 day

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