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Re: [PATCH] dma-buf: heaps: system: document system_cc_shared heap

by T.J. Mercier

On Thu, Apr 2, 2026 at 7:11 AM Jiri Pirko <jiri(a)resnulli.us> wrote: > > From: Jiri Pirko <jiri(a)nvidia.com> > > Document the system_cc_shared dma-buf heap that was introduced > recently. Describe its purpose, availability conditions and > relation to confidential computing VMs. > > Signed-off-by: Jiri Pirko <jiri(a)nvidia.com> > --- > Documentation/userspace-api/dma-buf-heaps.rst | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst > index 05445c83b79a..591732393e7d 100644 > --- a/Documentation/userspace-api/dma-buf-heaps.rst > +++ b/Documentation/userspace-api/dma-buf-heaps.rst > @@ -16,6 +16,14 @@ following heaps: > > - The ``system`` heap allocates virtually contiguous, cacheable, buffers. > > + - The ``system_cc_shared`` heap allocates virtually contiguous, cacheable, > + buffers using shared (decrypted) memory. It is only present on > + confidential computing (CoCo) VMs where memory encryption is active > + (e.g., AMD SEV, Intel TDX). The allocated pages have the encryption > + bit cleared, making them accessible for device DMA without TDISP > + support. On non-CoCo VMs configurations, this heap is "non-CoCo VM configurations" > + not registered. Doesn't seem like you need to wrap this line. with that: Reviewed-by: T.J.Mercier <tjmercier(a)google.com> > + > - The ``default_cma_region`` 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 Each paragraph starting with '-' confused me for a second there. Those aren't part of the diff. :)

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Re: [PATCH 1/7] drm/shmem-helper: Add lockdep asserts to vmap/vunmap

by Christian König

On 4/2/26 18:13, Bence Csókás wrote: > [Sie erhalten nicht häufig E-Mails von bence.csokas(a)arm.com. Weitere Informationen, warum dies wichtig ist, finden Sie unter https://aka.ms/LearnAboutSenderIdentification ] > > Hi, > > I just came across this commit while researching something else. > Original patch had too few context lines, so I here's the diff with `-U10`. > > On 3/18/25 20:22, Daniel Almeida wrote: >> From: Asahi Lina <lina(a)asahilina.net> >> >> Since commit 21aa27ddc582 ("drm/shmem-helper: Switch to reservation >> lock"), the drm_gem_shmem_vmap and drm_gem_shmem_vunmap functions >> require that the caller holds the DMA reservation lock for the object. >> Add lockdep assertions to help validate this. > > There were already lockdep assertions... Good point, I completely missed that. > >> Signed-off-by: Asahi Lina <lina(a)asahilina.net> >> Signed-off-by: Daniel Almeida <daniel.almeida(a)collabora.com> >> Reviewed-by: Christian König <christian.koenig(a)amd.com> >> Signed-off-by: Lyude Paul <lyude(a)redhat.com> >> Link: https://lore.kernel.org/r/20250318-drm-gem-shmem-v1-1-64b96511a84f@collabor… >> --- >> drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c >> index aa43265f4f4f..0b41f0346bad 100644 >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c >> @@ -341,20 +341,22 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin); >> * >> * Returns: >> * 0 on success or a negative error code on failure. >> */ >> int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem, >> struct iosys_map *map) >> { >> struct drm_gem_object *obj = &shmem->base; >> int ret = 0; >> >> + dma_resv_assert_held(obj->resv); >> + >> if (drm_gem_is_imported(obj)) { >> ret = dma_buf_vmap(obj->dma_buf, map); >> } else { >> pgprot_t prot = PAGE_KERNEL; >> >> dma_resv_assert_held(shmem->base.resv); > > ... right here, and > >> if (refcount_inc_not_zero(&shmem->vmap_use_count)) { >> iosys_map_set_vaddr(map, shmem->vaddr); >> return 0; >> @@ -401,20 +403,22 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_vmap_locked); >> * drops to zero. >> * >> * This function hides the differences between dma-buf imported and natively >> * allocated objects. >> */ >> void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem, >> struct iosys_map *map) >> { >> struct drm_gem_object *obj = &shmem->base; >> >> + dma_resv_assert_held(obj->resv); >> + >> if (drm_gem_is_imported(obj)) { >> dma_buf_vunmap(obj->dma_buf, map); >> } else { >> dma_resv_assert_held(shmem->base.resv); > > ...here. > >> if (refcount_dec_and_test(&shmem->vmap_use_count)) { >> vunmap(shmem->vaddr); >> shmem->vaddr = NULL; >> >> drm_gem_shmem_unpin_locked(shmem); > > Or were those insufficient for some reason? If so, should we keep both > of them, or should the older ones have been removed? The dma_buf_vmap()/dma_buf_vunmap() functions require the caller to be holding the reservation lock as well. So it kind of makes sense to move the assertions to the beginning of the functions. Regards, Christian. > > Bence

1 week, 3 days

[PATCH v4 0/8] dma-buf: heaps: Turn heaps into modules

by Maxime Ripard

Hi, The recent introduction of heaps in the optee driver [1] made possible the creation of heaps as modules. It's generally a good idea if possible, including for the already existing system and CMA heaps. The system one is pretty trivial, the CMA one is a bit more involved, especially since we have a call from kernel/dma/contiguous.c to the CMA heap code. This was solved by turning the logic around and making the CMA heap call into the contiguous DMA code. Let me know what you think, Maxime 1: https://lore.kernel.org/dri-devel/20250911135007.1275833-4-jens.wiklander@l… Signed-off-by: Maxime Ripard <mripard(a)kernel.org> --- Changes in v4: - Fix compilation failure - Rework to take into account OF_RESERVED_MEM - Fix regression making the default CMA area disappear if not created through the DT - Added some documentation and comments - Link to v3: https://lore.kernel.org/r/20260303-dma-buf-heaps-as-modules-v3-0-24344812c7… Changes in v3: - Squashed cma_get_name and cma_alloc/release patches - Fixed typo in Export dev_get_cma_area commit title - Fixed compilation failure with DMA_CMA but not OF_RESERVED_MEM - Link to v2: https://lore.kernel.org/r/20260227-dma-buf-heaps-as-modules-v2-0-454aee7e06… Changes in v2: - Collect tags - Don't export dma_contiguous_default_area anymore, but export dev_get_cma_area instead - Mentioned that heap modules can't be removed - Link to v1: https://lore.kernel.org/r/20260225-dma-buf-heaps-as-modules-v1-0-2109225a09… --- Maxime Ripard (8): dma: contiguous: Turn heap registration logic around dma: contiguous: Make dev_get_cma_area() a proper function dma: contiguous: Make dma_contiguous_default_area static dma: contiguous: Export dev_get_cma_area() mm: cma: Export cma_alloc(), cma_release() and cma_get_name() dma-buf: heaps: Export mem_accounting parameter dma-buf: heaps: cma: Turn the heap into a module dma-buf: heaps: system: Turn the heap into a module drivers/dma-buf/dma-heap.c | 1 + drivers/dma-buf/heaps/Kconfig | 4 +-- drivers/dma-buf/heaps/cma_heap.c | 22 +++---------- drivers/dma-buf/heaps/system_heap.c | 5 +++ include/linux/dma-buf/heaps/cma.h | 16 --------- include/linux/dma-map-ops.h | 14 ++++---- kernel/dma/contiguous.c | 66 +++++++++++++++++++++++++++++++++---- mm/cma.c | 3 ++ 8 files changed, 82 insertions(+), 49 deletions(-) --- base-commit: c081b71f11732ad2c443f170ab19c3ebe8a1a422 change-id: 20260225-dma-buf-heaps-as-modules-1034b3ec9f2a Best regards, -- Maxime Ripard <mripard(a)kernel.org>

1 week, 3 days

Re: [PATCH v5 0/2] dma-buf: heaps: system: add an option to allocate explicitly shared/decrypted memory

by Brian Starkey

Hi, I know I'm late to the party here... Like John, I'm also not very close to this stuff any more, but I agree with the other discussions: makes sense for this to be a separate heap, and cc_shared makes sense too. I'm not clear why the heap depends on !CONFIG_HIGHMEM, but I also don't know anything about SEV/TDX. -Brian On Wed, Mar 25, 2026 at 08:23:50PM +0000, Jiri Pirko wrote: > From: Jiri Pirko <jiri(a)nvidia.com> > > Confidential computing (CoCo) VMs/guests, such as AMD SEV and Intel TDX, > run with private/encrypted memory which creates a challenge > for devices that do not support DMA to it (no TDISP support). > > For kernel-only DMA operations, swiotlb bounce buffering provides a > transparent solution by copying data through shared memory. > However, the only way to get this memory into userspace is via the DMA > API's dma_alloc_pages()/dma_mmap_pages() type interfaces which limits > the use of the memory to a single DMA device, and is incompatible with > pin_user_pages(). > > These limitations are particularly problematic for the RDMA subsystem > which makes heavy use of pin_user_pages() and expects flexible memory > usage between many different DMA devices. > > This patch series enables userspace to explicitly request shared > (decrypted) memory allocations from new dma-buf system_cc_shared heap. > Userspace can mmap this memory and pass the dma-buf fd to other > existing importers such as RDMA or DRM devices to access the > memory. The DMA API is improved to allow the dma heap exporter to DMA > map the shared memory to each importing device. > > Based on dma-mapping-for-next e7442a68cd1ee797b585f045d348781e9c0dde0d > > Jiri Pirko (2): > dma-mapping: introduce DMA_ATTR_CC_SHARED for shared memory > dma-buf: heaps: system: add system_cc_shared heap for explicitly > shared memory > > drivers/dma-buf/heaps/system_heap.c | 103 ++++++++++++++++++++++++++-- > include/linux/dma-mapping.h | 10 +++ > include/trace/events/dma.h | 3 +- > kernel/dma/direct.h | 14 +++- > kernel/dma/mapping.c | 13 +++- > 5 files changed, 132 insertions(+), 11 deletions(-) > > -- > 2.51.1 >

1 week, 3 days

Re: [PATCH RFC 12/18] accel/qda: Add PRIME dma-buf import support

by Christian König

On 4/2/26 10:36, Ekansh Gupta wrote: > On 3/9/2026 12:29 PM, Ekansh Gupta wrote: >> >> On 2/24/2026 2:42 PM, Christian König wrote: >>> On 2/23/26 20:09, Ekansh Gupta wrote: >>>> [Sie erhalten nicht häufig E-Mails von ekansh.gupta(a)oss.qualcomm.com. Weitere Informationen, warum dies wichtig ist, finden Sie unter https://aka.ms/LearnAboutSenderIdentification ] >>>> >>>> Add PRIME dma-buf import support for QDA GEM buffer objects and integrate >>>> it with the existing per-process memory manager and IOMMU device model. >>>> >>>> The implementation extends qda_gem_obj to represent imported dma-bufs, >>>> including dma_buf references, attachment state, scatter-gather tables >>>> and an imported DMA address used for DSP-facing book-keeping. The >>>> qda_gem_prime_import() path handles reimports of buffers originally >>>> exported by QDA as well as imports of external dma-bufs, attaching them >>>> to the assigned IOMMU device >>> That is usually an absolutely clear NO-GO for DMA-bufs. Where exactly in the code is that? >> dma_buf_attach* to comute-cb iommu devices are critical for DSPs to access the buffer. >> This is needed if the buffer is exported by anyone other than QDA(say system heap). If this is not >> the correct way, what should be the right way here? On the current fastrpc driver also, >> the DMABUF is getting attached with iommu device[1] due to the same requirement. >> >> [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/dr… > > Hi Christian, > > Do you have any suggestions for the shared requirements? Well I don't fully understand what you are trying to do with the iommu. Usually it is the job of the exporter to provide the importer with DMA addresses which are valid for its device structure, that includes IOMMU mapping. Can you iterate what exactly this iommu group is and why you have to attach the imported buffers to it, how that attachment works and how lifetime is managed? Regards, Christian. > > I'm reworking on the next version and currently I don't see any other way > to handle dma_buf_attach* cases. > > //Ekansh > >>>> and mapping them through the memory manager >>>> for DSP access. The GEM free path is updated to unmap and detach >>>> imported buffers while preserving the existing behaviour for locally >>>> allocated memory. >>>> >>>> The PRIME fd-to-handle path is implemented in qda_prime_fd_to_handle(), >>>> which records the calling drm_file in a driver-private import context >>>> before invoking the core DRM helpers. The GEM import callback retrieves >>>> this context to ensure that an IOMMU device is assigned to the process >>>> and that imported buffers follow the same per-process IOMMU selection >>>> rules as natively allocated GEM objects. >>>> >>>> This patch prepares the driver for interoperable buffer sharing between >>>> QDA and other dma-buf capable subsystems while keeping IOMMU mapping and >>>> lifetime handling consistent with the existing GEM allocation flow. >>>> >>>> Signed-off-by: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> >>> ... >>> >>>> @@ -15,23 +16,29 @@ static int validate_gem_obj_for_mmap(struct qda_gem_obj *qda_gem_obj) >>>> qda_err(NULL, "Invalid GEM object size\n"); >>>> return -EINVAL; >>>> } >>>> - if (!qda_gem_obj->iommu_dev || !qda_gem_obj->iommu_dev->dev) { >>>> - qda_err(NULL, "Allocated buffer missing IOMMU device\n"); >>>> - return -EINVAL; >>>> - } >>>> - if (!qda_gem_obj->iommu_dev->dev) { >>>> - qda_err(NULL, "Allocated buffer missing IOMMU device\n"); >>>> - return -EINVAL; >>>> - } >>>> - if (!qda_gem_obj->virt) { >>>> - qda_err(NULL, "Allocated buffer missing virtual address\n"); >>>> - return -EINVAL; >>>> - } >>>> - if (qda_gem_obj->dma_addr == 0) { >>>> - qda_err(NULL, "Allocated buffer missing DMA address\n"); >>>> - return -EINVAL; >>>> + if (qda_gem_obj->is_imported) { >>> Absolutely clear NAK to that. Imported buffers *can't* be mmaped through the importer! >>> >>> Userspace needs to mmap() them through the exporter. >>> >>> If you absolutely have to map them through the importer for uAPI backward compatibility then there is dma_buf_mmap() for that, but this is clearly not the case here. >>> >>> ... >> Okay, the requirement is slightly different here. Any buffer which is not allocated using the >> QDA GEM interface needs to be attached to the iommu device for that particular process to >> enable DSP for the access. I should not call it `mmap` instead it should be called importing the >> buffer to a particular iommu context bank. With this definition, is it fine to keep it this way? Or >> should the dma_buf_attach* calls be moved to some other place? >>>> +static int qda_memory_manager_map_imported(struct qda_memory_manager *mem_mgr, >>>> + struct qda_gem_obj *gem_obj, >>>> + struct qda_iommu_device *iommu_dev) >>>> +{ >>>> + struct scatterlist *sg; >>>> + dma_addr_t dma_addr; >>>> + int ret = 0; >>>> + >>>> + if (!gem_obj->is_imported || !gem_obj->sgt || !iommu_dev) { >>>> + qda_err(NULL, "Invalid parameters for imported buffer mapping\n"); >>>> + return -EINVAL; >>>> + } >>>> + >>>> + gem_obj->iommu_dev = iommu_dev; >>>> + >>>> + sg = gem_obj->sgt->sgl; >>>> + if (sg) { >>>> + dma_addr = sg_dma_address(sg); >>>> + dma_addr += ((u64)iommu_dev->sid << 32); >>>> + >>>> + gem_obj->imported_dma_addr = dma_addr; >>> Well that looks like you are only using the first DMA address from the imported sgt. What about the others? >> I might have a proper appach for this now, will update in the next spin. >>> Regards, >>> Christian. >

1 week, 3 days

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