Linaro-mm-sig April 2025

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24 participants
100 discussions

Re: [PATCH v2 2/2] dma-buf: heaps: Give default CMA heap a fixed name

by Maxime Ripard

Hi Jared, Thanks for working on this On Tue, Apr 22, 2025 at 12:19:39PM -0700, Jared Kangas wrote: > The CMA heap's name in devtmpfs can vary depending on how the heap is > defined. Its name defaults to "reserved", but if a CMA area is defined > in the devicetree, the heap takes on the devicetree node's name, such as > "default-pool" or "linux,cma". To simplify naming, just name it > "default_cma", and keep a legacy node in place backed by the same > underlying structure for backwards compatibility. > > Signed-off-by: Jared Kangas <jkangas(a)redhat.com> > --- > Documentation/userspace-api/dma-buf-heaps.rst | 11 +++++++---- > drivers/dma-buf/heaps/Kconfig | 10 ++++++++++ > drivers/dma-buf/heaps/cma_heap.c | 14 +++++++++++++- > 3 files changed, 30 insertions(+), 5 deletions(-) > > diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst > index 535f49047ce64..577de813ba461 100644 > --- a/Documentation/userspace-api/dma-buf-heaps.rst > +++ b/Documentation/userspace-api/dma-buf-heaps.rst > @@ -19,7 +19,10 @@ following heaps: > - The ``cma`` heap allocates physically contiguous, cacheable, > buffers. Only present if a CMA region is present. Such a region is > usually created either through the kernel commandline through the > - `cma` parameter, a memory region Device-Tree node with the > - `linux,cma-default` property set, or through the `CMA_SIZE_MBYTES` or > - `CMA_SIZE_PERCENTAGE` Kconfig options. Depending on the platform, it > - might be called ``reserved``, ``linux,cma``, or ``default-pool``. > + ``cma`` parameter, a memory region Device-Tree node with the > + ``linux,cma-default`` property set, or through the ``CMA_SIZE_MBYTES`` or > + ``CMA_SIZE_PERCENTAGE`` Kconfig options. The heap's name in devtmpfs is > + ``default_cma``. For backwards compatibility, when the > + ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is > + created following legacy naming conventions; the legacy name might be > + ``reserved``, ``linux,cma``, or ``default-pool``. It looks like, in addition to documenting the new naming, you also changed all the backticks to double backticks. Why did you do so? It seems mostly unrelated to that patch, so it would be better in a separate patch. > diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig > index a5eef06c42264..83f3770fa820a 100644 > --- a/drivers/dma-buf/heaps/Kconfig > +++ b/drivers/dma-buf/heaps/Kconfig > @@ -12,3 +12,13 @@ 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_CMA_LEGACY > + bool "DMA-BUF CMA Heap" > + default y > + depends on DMABUF_HEAPS_CMA > + help > + Add a duplicate CMA-backed dma-buf heap with legacy naming derived > + from the CMA area's devicetree node, or "reserved" if the area is not > + defined in the devicetree. This uses the same underlying allocator as > + CONFIG_DMABUF_HEAPS_CMA. > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c > index e998d8ccd1dc6..cd742c961190d 100644 > --- a/drivers/dma-buf/heaps/cma_heap.c > +++ b/drivers/dma-buf/heaps/cma_heap.c > @@ -22,6 +22,7 @@ > #include <linux/slab.h> > #include <linux/vmalloc.h> > > +#define DEFAULT_CMA_NAME "default_cma" I appreciate this is kind of bikeshed-color territory, but I think "cma" would be a better option here. There's nothing "default" about it. > struct cma_heap { > struct dma_heap *heap; > @@ -394,15 +395,26 @@ static int __init __add_cma_heap(struct cma *cma, const char *name) > static int __init add_default_cma_heap(void) > { > struct cma *default_cma = dev_get_cma_area(NULL); > + const char *legacy_cma_name; > int ret; > > if (!default_cma) > return 0; > > - ret = __add_cma_heap(default_cma, cma_get_name(default_cma)); > + ret = __add_cma_heap(default_cma, DEFAULT_CMA_NAME); > if (ret) > return ret; > > + legacy_cma_name = cma_get_name(default_cma); > + > + if (IS_ENABLED(CONFIG_DMABUF_HEAPS_CMA_LEGACY) && > + strcmp(legacy_cma_name, DEFAULT_CMA_NAME)) { > + ret = __add_cma_heap(default_cma, legacy_cma_name); > + if (ret) > + pr_warn("cma_heap: failed to add legacy heap: %pe\n", > + ERR_PTR(-ret)); > + } > + It would also simplify this part, since you would always create the legacy heap. Maxime

12 hours, 12 minutes

[PATCH v3 0/2] dma-buf: heaps: Support carved-out heaps

by Maxime Ripard

Hi, This series is the follow-up of the discussion that John and I had some time ago here: https://lore.kernel.org/all/CANDhNCquJn6bH3KxKf65BWiTYLVqSd9892-xtFDHHqqyrr… The initial problem we were discussing was that I'm currently working on a platform which has a memory layout with ECC enabled. However, enabling the ECC has a number of drawbacks on that platform: lower performance, increased memory usage, etc. So for things like framebuffers, the trade-off isn't great and thus there's a memory region with ECC disabled to allocate from for such use cases. After a suggestion from John, I chose to first start using heap allocations flags to allow for userspace to ask for a particular ECC setup. This is then backed by a new heap type that runs from reserved memory chunks flagged as such, and the existing DT properties to specify the ECC properties. After further discussion, it was considered that flags were not the right solution, and relying on the names of the heaps would be enough to let userspace know the kind of buffer it deals with. Thus, even though the uAPI part of it has been dropped in this second version, we still need a driver to create heaps out of carved-out memory regions. In addition to the original usecase, a similar driver can be found in BSPs from most vendors, so I believe it would be a useful addition to the kernel. I submitted a draft PR to the DT schema for the bindings used in this PR: https://github.com/devicetree-org/dt-schema/pull/138 Let me know what you think, Maxime Signed-off-by: Maxime Ripard <mripard(a)kernel.org> --- Changes in v3: - Reworked global variable patch - Link to v2: https://lore.kernel.org/r/20250401-dma-buf-ecc-heap-v2-0-043fd006a1af@kerne… Changes in v2: - Add vmap/vunmap operations - Drop ECC flags uapi - Rebase on top of 6.14 - Link to v1: https://lore.kernel.org/r/20240515-dma-buf-ecc-heap-v1-0-54cbbd049511@kerne… --- Maxime Ripard (2): dma-buf: heaps: system: Remove global variable dma-buf: heaps: Introduce a new heap for reserved memory drivers/dma-buf/heaps/Kconfig | 8 + drivers/dma-buf/heaps/Makefile | 1 + drivers/dma-buf/heaps/carveout_heap.c | 360 ++++++++++++++++++++++++++++++++++ drivers/dma-buf/heaps/system_heap.c | 3 +- 4 files changed, 370 insertions(+), 2 deletions(-) --- base-commit: fcbf30774e82a441890b722bf0c26542fb82150f change-id: 20240515-dma-buf-ecc-heap-28a311d2c94e Best regards, -- Maxime Ripard <mripard(a)kernel.org>

23 hours, 55 minutes

Re: [PATCH 2/4] bpf: Add dmabuf iterator

by T.J. Mercier

On Tue, Apr 22, 2025 at 4:01 PM Alexei Starovoitov <alexei.starovoitov(a)gmail.com> wrote: > > On Tue, Apr 22, 2025 at 12:57 PM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > On Mon, Apr 21, 2025 at 4:39 PM Alexei Starovoitov > > <alexei.starovoitov(a)gmail.com> wrote: > > > > > > On Mon, Apr 21, 2025 at 1:40 PM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > > > > > > > new file mode 100644 > > > > > > index 000000000000..b4b8be1d6aa4 > > > > > > --- /dev/null > > > > > > +++ b/kernel/bpf/dmabuf_iter.c > > > > > > > > > > Maybe we should add this file to drivers/dma-buf. I would like to > > > > > hear other folks thoughts on this. > > > > > > > > This is fine with me, and would save us the extra > > > > CONFIG_DMA_SHARED_BUFFER check that's currently needed in > > > > kernel/bpf/Makefile but would require checking CONFIG_BPF instead. > > > > Sumit / Christian any objections to moving the dmabuf bpf iterator > > > > implementation into drivers/dma-buf? > > > > > > The driver directory would need to 'depends on BPF_SYSCALL'. > > > Are you sure you want this? > > > imo kernel/bpf/ is fine for this. > > > > I don't have a strong preference so either way is fine with me. The > > main difference I see is maintainership. > > > > > You also probably want > > > .feature = BPF_ITER_RESCHED > > > in bpf_dmabuf_reg_info. > > > > Thank you, this looks like a good idea. > > > > > Also have you considered open coded iterator for dmabufs? > > > Would it help with the interface to user space? > > > > I read through the open coded iterator patches, and it looks like they > > would be slightly more efficient by avoiding seq_file overhead. As far > > as the interface to userspace, for the purpose of replacing what's > > currently exposed by CONFIG_DMABUF_SYSFS_STATS I don't think there is > > a difference. However it looks like if I were to try to replace all of > > our userspace analysis of dmabufs with a single bpf program then an > > open coded iterator would make that much easier. I had not considered > > attempting that. > > > > One problem I see with open coded iterators is that support is much > > more recent (2023 vs 2020). We support longterm stable kernels (back > > to 5.4 currently but probably 5.10 by the time this would be used), so > > it seems like it would be harder to backport the kernel support for an > > open-coded iterator that far since it only goes back as far as 6.6 > > now. Actually it doesn't look like it is possible while also > > maintaining the stable ABI we provide to device vendors. Which means > > we couldn't get rid of the dmabuf sysfs stats userspace dependency > > until 6.1 EOL in Dec. 2027. :\ So I'm in favor of a traditional bpf > > iterator here for now. > > Fair enough, but please implement both and backport only > the old style pinned iterator. Ok, will do. > The code will be mostly shared between them. > bpf_iter_dmabuf_new/_next will be more flexible with more > options to return data to user space. Like android can invent > their own binary format. Pack into it in a bpf prog, send to > bpf ringbuf and unmarshal efficiently in user space. > Instead of being limited to text output that pinned iterators > are supposed to do usually. Also a neat idea! > You can do binary with bpf_seq_write() too, but it's rare. > > Also please provide full bpf prog that you'll use in production > in a selftest instead of trivial: > +SEC("iter/dmabuf") > +int dmabuf_collector(struct bpf_iter__dmabuf *ctx) > > just to make sure it's tested end to end and future changes > won't break it. The final bpf program should be something pretty close to that, but I'll start working on the AOSP side as well so I can put up patches. > > pw-bot: cr

2 days, 14 hours

Re: [PATCH v2 0/2] dma-buf: heaps: Use constant name for CMA heap

by Sumit Semwal

Hello Jared, On Wed, 23 Apr 2025 at 00:49, Jared Kangas <jkangas(a)redhat.com> wrote: > > Hi all, > > This patch series is based on a previous discussion around CMA heap > naming. [1] The heap's name depends on the device name, which is > generally "reserved", "linux,cma", or "default-pool", but could be any > arbitrary name given to the default CMA area in the devicetree. For a > consistent userspace interface, the series introduces a constant name > for the CMA heap, and for backwards compatibility, an additional Kconfig > that controls the creation of a legacy-named heap with the same CMA > backing. > > The ideas to handle backwards compatibility in [1] are to either use a > symlink or add a heap node with a duplicate minor. However, I assume > that we don't want to create symlinks in /dev from module initcalls, and > attempting to duplicate minors would cause device_create() to fail. > Because of these drawbacks, after brainstorming with Maxime Ripard, I > went with creating a new node in devtmpfs with its own minor. This > admittedly makes it a little unclear that the old and new nodes are > backed by the same heap when both are present. The only approach that I > think would provide total clarity on this in userspace is symlinking, > which seemed like a fairly involved solution for devtmpfs, but if I'm > wrong on this, please let me know. Thanks indeed for this patch; just one minor nit: the link referred to as [1] here seems to be missing. Could you please add it? This would make it easier to follow the chain of discussion in posterity. > > Changelog: > v2: Use tabs instead of spaces for large vertical alignment. > > Jared Kangas (2): > dma-buf: heaps: Parameterize heap name in __add_cma_heap() > dma-buf: heaps: Give default CMA heap a fixed name > > Documentation/userspace-api/dma-buf-heaps.rst | 11 ++++--- > drivers/dma-buf/heaps/Kconfig | 10 +++++++ > drivers/dma-buf/heaps/cma_heap.c | 30 ++++++++++++++----- > 3 files changed, 40 insertions(+), 11 deletions(-) > > -- > 2.49.0 > Best, Sumit

2 days, 16 hours

Re: [PATCH v2 2/2] dma-buf: heaps: Give default CMA heap a fixed name

by John Stultz

On Tue, Apr 22, 2025 at 12:19 PM Jared Kangas <jkangas(a)redhat.com> wrote: > > The CMA heap's name in devtmpfs can vary depending on how the heap is > defined. Its name defaults to "reserved", but if a CMA area is defined > in the devicetree, the heap takes on the devicetree node's name, such as > "default-pool" or "linux,cma". To simplify naming, just name it > "default_cma", and keep a legacy node in place backed by the same > underlying structure for backwards compatibility. > > Signed-off-by: Jared Kangas <jkangas(a)redhat.com> Once again, thanks for working out how to improve the standard naming while keeping compatibility. I do still hope we can get to the point where other cma regions can be registered as heaps with unique/purpose-specific names, but I can see having a standard name for the default region is a nice improvement. Acked-by: John Stultz <jstultz(a)google.com> thanks -john

3 days, 9 hours

Re: [PATCH v2 1/2] dma-buf: heaps: Parameterize heap name in __add_cma_heap()

by John Stultz

On Tue, Apr 22, 2025 at 12:19 PM Jared Kangas <jkangas(a)redhat.com> wrote: > > Prepare for the introduction of a fixed-name CMA heap by replacing the > unused void pointer parameter in __add_cma_heap() with the heap name. > > Signed-off-by: Jared Kangas <jkangas(a)redhat.com> Thanks so much for taking this effort on. Looks good to me! Acked-by: John Stultz <jstultz(a)google.com>

3 days, 9 hours

Re: [PATCH 2/4] bpf: Add dmabuf iterator

by T.J. Mercier

On Mon, Apr 21, 2025 at 4:39 PM Alexei Starovoitov <alexei.starovoitov(a)gmail.com> wrote: > > On Mon, Apr 21, 2025 at 1:40 PM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > > > new file mode 100644 > > > > index 000000000000..b4b8be1d6aa4 > > > > --- /dev/null > > > > +++ b/kernel/bpf/dmabuf_iter.c > > > > > > Maybe we should add this file to drivers/dma-buf. I would like to > > > hear other folks thoughts on this. > > > > This is fine with me, and would save us the extra > > CONFIG_DMA_SHARED_BUFFER check that's currently needed in > > kernel/bpf/Makefile but would require checking CONFIG_BPF instead. > > Sumit / Christian any objections to moving the dmabuf bpf iterator > > implementation into drivers/dma-buf? > > The driver directory would need to 'depends on BPF_SYSCALL'. > Are you sure you want this? > imo kernel/bpf/ is fine for this. I don't have a strong preference so either way is fine with me. The main difference I see is maintainership. > You also probably want > .feature = BPF_ITER_RESCHED > in bpf_dmabuf_reg_info. Thank you, this looks like a good idea. > Also have you considered open coded iterator for dmabufs? > Would it help with the interface to user space? I read through the open coded iterator patches, and it looks like they would be slightly more efficient by avoiding seq_file overhead. As far as the interface to userspace, for the purpose of replacing what's currently exposed by CONFIG_DMABUF_SYSFS_STATS I don't think there is a difference. However it looks like if I were to try to replace all of our userspace analysis of dmabufs with a single bpf program then an open coded iterator would make that much easier. I had not considered attempting that. One problem I see with open coded iterators is that support is much more recent (2023 vs 2020). We support longterm stable kernels (back to 5.4 currently but probably 5.10 by the time this would be used), so it seems like it would be harder to backport the kernel support for an open-coded iterator that far since it only goes back as far as 6.6 now. Actually it doesn't look like it is possible while also maintaining the stable ABI we provide to device vendors. Which means we couldn't get rid of the dmabuf sysfs stats userspace dependency until 6.1 EOL in Dec. 2027. :\ So I'm in favor of a traditional bpf iterator here for now.

3 days, 11 hours

Re: [PATCH 0/3] uio/dma-buf: Give UIO users access to DMA addresses.

by Jason Gunthorpe

On Mon, Apr 14, 2025 at 09:21:25PM +0200, Thomas Petazzoni wrote: > > "UIO is a broken legacy mess, so let's add more broken things > > to it as broken + broken => still broken, so no harm done", am I > > getting that right? > > Who says UIO is a "broken legacy mess"? Only you says so. I don't see > any indication anywhere in the kernel tree suggesting that UIO is > considered a broken legacy mess. Explain what the difference is between UIO and VFIO, especially VFIO no-iommu mode? I've always understood that UIO is for very simple devices that cannot do DMA. So it's very simple operating model and simple security work fine. IMHO, if the can use DMA it should use VFIO. If you have no iommu then you should use the VFIO unsafe no-iommu path. It still provides a solid framework. As to this series, I have seen a number of requests to improve the VFIO no-iommu path to allow working with the existing IOAS scheme to register memory but to allow the kernel the return the no-iommu DMAable address of the IOAS pinned memory. This would replace the hacky use of mlock and /proc/XX/pagemap that people use today. If that were done, could you use VFIO no-iommu? > Keep in mind that when you're running code as root, you can load a > kernel module, which can do anything on the system security-wise. So > letting UIO expose MMIO registers of devices to userspace applications > running as root is not any worse than that. That isn't fully true.. UIO isn't fitting into the security model by allowing DMA capable devices to be exposed without checking for CAP_SYS_RAW_IO first. Jason

3 days, 13 hours

[PATCH] dma-buf: system_heap: No separate allocation for attachment sg_tables

by T.J. Mercier

struct dma_heap_attachment is a separate allocation from the struct sg_table it contains, but there is no reason for this. Let's use the slab allocator just once instead of twice for dma_heap_attachment. Signed-off-by: T.J. Mercier <tjmercier(a)google.com> --- drivers/dma-buf/heaps/system_heap.c | 43 ++++++++++++----------------- 1 file changed, 17 insertions(+), 26 deletions(-) diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c index 26d5dc89ea16..bee10c400cf0 100644 --- a/drivers/dma-buf/heaps/system_heap.c +++ b/drivers/dma-buf/heaps/system_heap.c @@ -35,7 +35,7 @@ struct system_heap_buffer { struct dma_heap_attachment { struct device *dev; - struct sg_table *table; + struct sg_table table; struct list_head list; bool mapped; }; @@ -54,29 +54,22 @@ static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP}; static const unsigned int orders[] = {8, 4, 0}; #define NUM_ORDERS ARRAY_SIZE(orders) -static struct sg_table *dup_sg_table(struct sg_table *table) +static int dup_sg_table(struct sg_table *from, struct sg_table *to) { - struct sg_table *new_table; - int ret, i; struct scatterlist *sg, *new_sg; + int ret, i; - new_table = kzalloc(sizeof(*new_table), GFP_KERNEL); - if (!new_table) - return ERR_PTR(-ENOMEM); - - ret = sg_alloc_table(new_table, table->orig_nents, GFP_KERNEL); - if (ret) { - kfree(new_table); - return ERR_PTR(-ENOMEM); - } + ret = sg_alloc_table(to, from->orig_nents, GFP_KERNEL); + if (ret) + return ret; - new_sg = new_table->sgl; - for_each_sgtable_sg(table, sg, i) { + new_sg = to->sgl; + for_each_sgtable_sg(from, sg, i) { sg_set_page(new_sg, sg_page(sg), sg->length, sg->offset); new_sg = sg_next(new_sg); } - return new_table; + return 0; } static int system_heap_attach(struct dma_buf *dmabuf, @@ -84,19 +77,18 @@ static int system_heap_attach(struct dma_buf *dmabuf, { struct system_heap_buffer *buffer = dmabuf->priv; struct dma_heap_attachment *a; - struct sg_table *table; + int ret; a = kzalloc(sizeof(*a), GFP_KERNEL); if (!a) return -ENOMEM; - table = dup_sg_table(&buffer->sg_table); - if (IS_ERR(table)) { + ret = dup_sg_table(&buffer->sg_table, &a->table); + if (ret) { kfree(a); - return -ENOMEM; + return ret; } - a->table = table; a->dev = attachment->dev; INIT_LIST_HEAD(&a->list); a->mapped = false; @@ -120,8 +112,7 @@ static void system_heap_detach(struct dma_buf *dmabuf, list_del(&a->list); mutex_unlock(&buffer->lock); - sg_free_table(a->table); - kfree(a->table); + sg_free_table(&a->table); kfree(a); } @@ -129,7 +120,7 @@ static struct sg_table *system_heap_map_dma_buf(struct dma_buf_attachment *attac enum dma_data_direction direction) { struct dma_heap_attachment *a = attachment->priv; - struct sg_table *table = a->table; + struct sg_table *table = &a->table; int ret; ret = dma_map_sgtable(attachment->dev, table, direction, 0); @@ -164,7 +155,7 @@ static int system_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf, list_for_each_entry(a, &buffer->attachments, list) { if (!a->mapped) continue; - dma_sync_sgtable_for_cpu(a->dev, a->table, direction); + dma_sync_sgtable_for_cpu(a->dev, &a->table, direction); } mutex_unlock(&buffer->lock); @@ -185,7 +176,7 @@ static int system_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf, list_for_each_entry(a, &buffer->attachments, list) { if (!a->mapped) continue; - dma_sync_sgtable_for_device(a->dev, a->table, direction); + dma_sync_sgtable_for_device(a->dev, &a->table, direction); } mutex_unlock(&buffer->lock); base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444 -- 2.49.0.805.g082f7c87e0-goog

3 days, 15 hours

Re: [PATCH 2/4] bpf: Add dmabuf iterator

by T.J. Mercier

On Mon, Apr 21, 2025 at 10:58 AM Song Liu <song(a)kernel.org> wrote: > > On Mon, Apr 14, 2025 at 3:53 PM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > The dmabuf iterator traverses the list of all DMA buffers. The list is > > maintained only when CONFIG_DEBUG_FS is enabled. > > > > DMA buffers are refcounted through their associated struct file. A > > reference is taken on each buffer as the list is iterated to ensure each > > buffer persists for the duration of the bpf program execution without > > holding the list mutex. > > > > Signed-off-by: T.J. Mercier <tjmercier(a)google.com> > > --- > > include/linux/btf_ids.h | 1 + > > kernel/bpf/Makefile | 3 + > > kernel/bpf/dmabuf_iter.c | 130 +++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 134 insertions(+) > > create mode 100644 kernel/bpf/dmabuf_iter.c > > > > diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h > > index 139bdececdcf..899ead57d89d 100644 > > --- a/include/linux/btf_ids.h > > +++ b/include/linux/btf_ids.h > > @@ -284,5 +284,6 @@ extern u32 bpf_cgroup_btf_id[]; > > extern u32 bpf_local_storage_map_btf_id[]; > > extern u32 btf_bpf_map_id[]; > > extern u32 bpf_kmem_cache_btf_id[]; > > +extern u32 bpf_dmabuf_btf_id[]; > > This is not necessary. See below. > > > > > #endif > > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile > > index 70502f038b92..5b30d37ef055 100644 > > --- a/kernel/bpf/Makefile > > +++ b/kernel/bpf/Makefile > > @@ -53,6 +53,9 @@ obj-$(CONFIG_BPF_SYSCALL) += relo_core.o > > obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o > > obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o > > obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o > > +ifeq ($(CONFIG_DEBUG_FS),y) > > +obj-$(CONFIG_BPF_SYSCALL) += dmabuf_iter.o > > +endif > > > > CFLAGS_REMOVE_percpu_freelist.o = $(CC_FLAGS_FTRACE) > > CFLAGS_REMOVE_bpf_lru_list.o = $(CC_FLAGS_FTRACE) > > diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c > > new file mode 100644 > > index 000000000000..b4b8be1d6aa4 > > --- /dev/null > > +++ b/kernel/bpf/dmabuf_iter.c > > Maybe we should add this file to drivers/dma-buf. I would like to > hear other folks thoughts on this. This is fine with me, and would save us the extra CONFIG_DMA_SHARED_BUFFER check that's currently needed in kernel/bpf/Makefile but would require checking CONFIG_BPF instead. Sumit / Christian any objections to moving the dmabuf bpf iterator implementation into drivers/dma-buf? > > @@ -0,0 +1,130 @@ > > +// SPDX-License-Identifier: GPL-2.0-only > > +/* Copyright (c) 2025 Google LLC */ > > +#include <linux/bpf.h> > > +#include <linux/btf_ids.h> > > +#include <linux/dma-buf.h> > > +#include <linux/kernel.h> > > +#include <linux/seq_file.h> > > + > > +BTF_ID_LIST_GLOBAL_SINGLE(bpf_dmabuf_btf_id, struct, dma_buf) > > Use BTF_ID_LIST_SINGLE(), then we don't need this in btf_ids.h > > > +DEFINE_BPF_ITER_FUNC(dmabuf, struct bpf_iter_meta *meta, struct dma_buf *dmabuf) > > + > > +static void *dmabuf_iter_seq_start(struct seq_file *seq, loff_t *pos) > > +{ > > + struct dma_buf *dmabuf, *ret = NULL; > > + > > + if (*pos) { > > + *pos = 0; > > + return NULL; > > + } > > + /* Look for the first buffer we can obtain a reference to. > > + * The list mutex does not protect a dmabuf's refcount, so it can be > > + * zeroed while we are iterating. Therefore we cannot call get_dma_buf() > > + * since the caller of this program may not already own a reference to > > + * the buffer. > > + */ > > We should use kernel comment style for new code. IOW, > /* > * Look for ... > */ > > > Thanks, > Song Thanks, I have incorporated all of your comments and retested. I will give some time for more feedback before sending a v2. > > [...]

4 days, 11 hours

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