Linaro-mm-sig May 2025

linaro-mm-sig@lists.linaro.org

26 participants
99 discussions

Re: [RFC PATCH 00/12] Private MMIO support for private assigned dev

by Jason Gunthorpe

On Fri, May 16, 2025 at 12:04:04AM +0800, Xu Yilun wrote: > > arches this was mostly invisible to the hypervisor? > > Attest & Accept can be invisible to hypervisor, or host just help pass > data blobs between guest, firmware & device. > > Bind cannot be host agnostic, host should be aware not to touch device > after Bind. I'm not sure this is fully true, this could be a Intel thing. When the vPCI is created the host can already know it shouldn't touch the PCI device anymore and the secure world would enforce that when it gets a bind command. The fact it hasn't been locked out immediately at vPCI creation time is sort of a detail that doesn't matter, IMHO. > > It might be reasonable to have VFIO reach into iommufd to do that on > > an already existing iommufd VDEVICE object. A little weird, but we > > could probably make that work. > > Mm, Are you proposing an uAPI in VFIO, and a kAPI from VFIO -> IOMMUFD like: > > ioctl(vfio_fd, VFIO_DEVICE_ATTACH_VDEV, vdev_id) > -> iommufd_device_attach_vdev() > -> tsm_tdi_bind() Not ATTACH, you wanted BIND. You could have a VFIO_DEVICE_BIND(iommufd vdevice id) > > sees VFIO remove the S-EPT and release the KVM, then have iommufd > > destroy the VDEVICE object. > > Regarding VM destroy, TDX Connect has more enforcement, VM could only be > destroyed after all assigned CC vPCI devices are destroyed. And KVM destroys the VM? > Nowadays, VFIO already holds KVM reference, so we need > > close(vfio_fd) > -> iommufd_device_detach_vdev() This doesn't happen though, it destroys the normal device (idev) which the vdevice is stacked on top of. You'd have to make normal device destruction trigger vdevice destruction > -> tsm_tdi_unbind() > -> tdi stop > -> callback to VFIO, dmabuf_move_notify(revoke) > -> KVM unmap MMIO > -> tdi metadata remove This omits the viommu. It won't get destroyed until the iommufd closes, so iommufd will be holding the kvm and it will do the final put. Jason

5 days, 23 hours

Re: [PATCH 2/2] dmabuf/heaps: implement DMA_BUF_IOCTL_RW_FILE for system_heap

by Christian König

On 5/15/25 16:03, wangtao wrote: > [wangtao] My Test Configuration (CPU 1GHz, 5-test average): > Allocation: 32x32MB buffer creation > - dmabuf 53ms vs. udmabuf 694ms (10X slower) > - Note: shmem shows excessive allocation time Yeah, that is something already noted by others as well. But that is orthogonal. > > Read 1024MB File: > - dmabuf direct 326ms vs. udmabuf direct 461ms (40% slower) > - Note: pin_user_pages_fast consumes majority CPU cycles > > Key function call timing: See details below. Those aren't valid, you are comparing different functionalities here. Please try using udmabuf with sendfile() as confirmed to be working by T.J. Regards, Christian.

6 days, 3 hours

Re: [PATCH v4 2/9] dma-fence: Use a flag for 64-bit seqnos

by Christian König

Hey drm-misc maintainers, can you guys please backmerge drm-next into drm-misc-next? I want to push this patch here but it depends on changes which are partially in drm-next and partially in drm-misc-next. Thanks in advance, Christian. On 5/15/25 11:49, Tvrtko Ursulin wrote: > With the goal of reducing the need for drivers to touch (and dereference) > fence->ops, we move the 64-bit seqnos flag from struct dma_fence_ops to > the fence->flags. > > Drivers which were setting this flag are changed to use new > dma_fence_init64() instead of dma_fence_init(). > > v2: > * Streamlined init and added kerneldoc. > * Rebase for amdgpu userq which landed since. > > Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> > Reviewed-by: Christian König <christian.koenig(a)amd.com> # v1 > --- > drivers/dma-buf/dma-fence-chain.c | 5 +- > drivers/dma-buf/dma-fence.c | 69 ++++++++++++++----- > .../drm/amd/amdgpu/amdgpu_eviction_fence.c | 7 +- > .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c | 5 +- > .../gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c | 5 +- > include/linux/dma-fence.h | 14 ++-- > 6 files changed, 64 insertions(+), 41 deletions(-) > > diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c > index 90424f23fd73..a8a90acf4f34 100644 > --- a/drivers/dma-buf/dma-fence-chain.c > +++ b/drivers/dma-buf/dma-fence-chain.c > @@ -218,7 +218,6 @@ static void dma_fence_chain_set_deadline(struct dma_fence *fence, > } > > const struct dma_fence_ops dma_fence_chain_ops = { > - .use_64bit_seqno = true, > .get_driver_name = dma_fence_chain_get_driver_name, > .get_timeline_name = dma_fence_chain_get_timeline_name, > .enable_signaling = dma_fence_chain_enable_signaling, > @@ -262,8 +261,8 @@ void dma_fence_chain_init(struct dma_fence_chain *chain, > seqno = max(prev->seqno, seqno); > } > > - dma_fence_init(&chain->base, &dma_fence_chain_ops, > - &chain->lock, context, seqno); > + dma_fence_init64(&chain->base, &dma_fence_chain_ops, &chain->lock, > + context, seqno); > > /* > * Chaining dma_fence_chain container together is only allowed through > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > index f0cdd3e99d36..705b59787731 100644 > --- a/drivers/dma-buf/dma-fence.c > +++ b/drivers/dma-buf/dma-fence.c > @@ -989,24 +989,9 @@ void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq) > } > EXPORT_SYMBOL(dma_fence_describe); > > -/** > - * dma_fence_init - Initialize a custom fence. > - * @fence: the fence to initialize > - * @ops: the dma_fence_ops for operations on this fence > - * @lock: the irqsafe spinlock to use for locking this fence > - * @context: the execution context this fence is run on > - * @seqno: a linear increasing sequence number for this context > - * > - * Initializes an allocated fence, the caller doesn't have to keep its > - * refcount after committing with this fence, but it will need to hold a > - * refcount again if &dma_fence_ops.enable_signaling gets called. > - * > - * context and seqno are used for easy comparison between fences, allowing > - * to check which fence is later by simply using dma_fence_later(). > - */ > -void > -dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > - spinlock_t *lock, u64 context, u64 seqno) > +static void > +__dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > + spinlock_t *lock, u64 context, u64 seqno, unsigned long flags) > { > BUG_ON(!lock); > BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name); > @@ -1017,9 +1002,55 @@ dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > fence->lock = lock; > fence->context = context; > fence->seqno = seqno; > - fence->flags = 0UL; > + fence->flags = flags; > fence->error = 0; > > trace_dma_fence_init(fence); > } > + > +/** > + * dma_fence_init - Initialize a custom fence. > + * @fence: the fence to initialize > + * @ops: the dma_fence_ops for operations on this fence > + * @lock: the irqsafe spinlock to use for locking this fence > + * @context: the execution context this fence is run on > + * @seqno: a linear increasing sequence number for this context > + * > + * Initializes an allocated fence, the caller doesn't have to keep its > + * refcount after committing with this fence, but it will need to hold a > + * refcount again if &dma_fence_ops.enable_signaling gets called. > + * > + * context and seqno are used for easy comparison between fences, allowing > + * to check which fence is later by simply using dma_fence_later(). > + */ > +void > +dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > + spinlock_t *lock, u64 context, u64 seqno) > +{ > + __dma_fence_init(fence, ops, lock, context, seqno, 0UL); > +} > EXPORT_SYMBOL(dma_fence_init); > + > +/** > + * dma_fence_init64 - Initialize a custom fence with 64-bit seqno support. > + * @fence: the fence to initialize > + * @ops: the dma_fence_ops for operations on this fence > + * @lock: the irqsafe spinlock to use for locking this fence > + * @context: the execution context this fence is run on > + * @seqno: a linear increasing sequence number for this context > + * > + * Initializes an allocated fence, the caller doesn't have to keep its > + * refcount after committing with this fence, but it will need to hold a > + * refcount again if &dma_fence_ops.enable_signaling gets called. > + * > + * Context and seqno are used for easy comparison between fences, allowing > + * to check which fence is later by simply using dma_fence_later(). > + */ > +void > +dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops, > + spinlock_t *lock, u64 context, u64 seqno) > +{ > + __dma_fence_init(fence, ops, lock, context, seqno, > + BIT(DMA_FENCE_FLAG_SEQNO64_BIT)); > +} > +EXPORT_SYMBOL(dma_fence_init64); > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c > index 1a7469543db5..79713421bffe 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c > @@ -134,7 +134,6 @@ static bool amdgpu_eviction_fence_enable_signaling(struct dma_fence *f) > } > > static const struct dma_fence_ops amdgpu_eviction_fence_ops = { > - .use_64bit_seqno = true, > .get_driver_name = amdgpu_eviction_fence_get_driver_name, > .get_timeline_name = amdgpu_eviction_fence_get_timeline_name, > .enable_signaling = amdgpu_eviction_fence_enable_signaling, > @@ -160,9 +159,9 @@ amdgpu_eviction_fence_create(struct amdgpu_eviction_fence_mgr *evf_mgr) > ev_fence->evf_mgr = evf_mgr; > get_task_comm(ev_fence->timeline_name, current); > spin_lock_init(&ev_fence->lock); > - dma_fence_init(&ev_fence->base, &amdgpu_eviction_fence_ops, > - &ev_fence->lock, evf_mgr->ev_fence_ctx, > - atomic_inc_return(&evf_mgr->ev_fence_seq)); > + dma_fence_init64(&ev_fence->base, &amdgpu_eviction_fence_ops, > + &ev_fence->lock, evf_mgr->ev_fence_ctx, > + atomic_inc_return(&evf_mgr->ev_fence_seq)); > return ev_fence; > } > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c > index 029cb24c28b3..5e92d00a591f 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq_fence.c > @@ -239,8 +239,8 @@ static int amdgpu_userq_fence_create(struct amdgpu_usermode_queue *userq, > fence = &userq_fence->base; > userq_fence->fence_drv = fence_drv; > > - dma_fence_init(fence, &amdgpu_userq_fence_ops, &userq_fence->lock, > - fence_drv->context, seq); > + dma_fence_init64(fence, &amdgpu_userq_fence_ops, &userq_fence->lock, > + fence_drv->context, seq); > > amdgpu_userq_fence_driver_get(fence_drv); > dma_fence_get(fence); > @@ -334,7 +334,6 @@ static void amdgpu_userq_fence_release(struct dma_fence *f) > } > > static const struct dma_fence_ops amdgpu_userq_fence_ops = { > - .use_64bit_seqno = true, > .get_driver_name = amdgpu_userq_fence_get_driver_name, > .get_timeline_name = amdgpu_userq_fence_get_timeline_name, > .signaled = amdgpu_userq_fence_signaled, > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c > index 51cddfa3f1e8..5d26797356a3 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_tlb_fence.c > @@ -71,7 +71,6 @@ static void amdgpu_tlb_fence_work(struct work_struct *work) > } > > static const struct dma_fence_ops amdgpu_tlb_fence_ops = { > - .use_64bit_seqno = true, > .get_driver_name = amdgpu_tlb_fence_get_driver_name, > .get_timeline_name = amdgpu_tlb_fence_get_timeline_name > }; > @@ -101,8 +100,8 @@ void amdgpu_vm_tlb_fence_create(struct amdgpu_device *adev, struct amdgpu_vm *vm > INIT_WORK(&f->work, amdgpu_tlb_fence_work); > spin_lock_init(&f->lock); > > - dma_fence_init(&f->base, &amdgpu_tlb_fence_ops, &f->lock, > - vm->tlb_fence_context, atomic64_read(&vm->tlb_seq)); > + dma_fence_init64(&f->base, &amdgpu_tlb_fence_ops, &f->lock, > + vm->tlb_fence_context, atomic64_read(&vm->tlb_seq)); > > /* TODO: We probably need a separate wq here */ > dma_fence_get(&f->base); > diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h > index 48b5202c531d..a34a0dcdc446 100644 > --- a/include/linux/dma-fence.h > +++ b/include/linux/dma-fence.h > @@ -97,6 +97,7 @@ struct dma_fence { > }; > > enum dma_fence_flag_bits { > + DMA_FENCE_FLAG_SEQNO64_BIT, > DMA_FENCE_FLAG_SIGNALED_BIT, > DMA_FENCE_FLAG_TIMESTAMP_BIT, > DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, > @@ -124,14 +125,6 @@ struct dma_fence_cb { > * > */ > struct dma_fence_ops { > - /** > - * @use_64bit_seqno: > - * > - * True if this dma_fence implementation uses 64bit seqno, false > - * otherwise. > - */ > - bool use_64bit_seqno; > - > /** > * @get_driver_name: > * > @@ -262,6 +255,9 @@ struct dma_fence_ops { > void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > spinlock_t *lock, u64 context, u64 seqno); > > +void dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops, > + spinlock_t *lock, u64 context, u64 seqno); > + > void dma_fence_release(struct kref *kref); > void dma_fence_free(struct dma_fence *fence); > void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq); > @@ -454,7 +450,7 @@ static inline bool __dma_fence_is_later(struct dma_fence *fence, u64 f1, u64 f2) > * 32bit sequence numbers. Use a 64bit compare when the driver says to > * do so. > */ > - if (fence->ops->use_64bit_seqno) > + if (test_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags)) > return f1 > f2; > > return (int)(lower_32_bits(f1) - lower_32_bits(f2)) > 0;

6 days, 4 hours

Re: [PATCH bpf-next v6 5/5] selftests/bpf: Add test for open coded dmabuf_iter

by T.J. Mercier

On Wed, May 14, 2025 at 2:00 PM Song Liu <song(a)kernel.org> wrote: > > On Tue, May 13, 2025 at 9:36 AM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > Use the same test buffers as the traditional iterator and a new BPF map > > to verify the test buffers can be found with the open coded dmabuf > > iterator. > > > > Signed-off-by: T.J. Mercier <tjmercier(a)google.com> > > Acked-by: Christian König <christian.koenig(a)amd.com> > > Acked-by: Song Liu <song(a)kernel.org> > > --- > > .../testing/selftests/bpf/bpf_experimental.h | 5 +++ > > .../selftests/bpf/prog_tests/dmabuf_iter.c | 41 +++++++++++++++++++ > > .../testing/selftests/bpf/progs/dmabuf_iter.c | 38 +++++++++++++++++ > > 3 files changed, 84 insertions(+) > > > > diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h > > index 6535c8ae3c46..5e512a1d09d1 100644 > > --- a/tools/testing/selftests/bpf/bpf_experimental.h > > +++ b/tools/testing/selftests/bpf/bpf_experimental.h > > @@ -591,4 +591,9 @@ extern int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) __weak __ksym > > extern struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) __weak __ksym; > > extern void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) __weak __ksym; > > > > +struct bpf_iter_dmabuf; > > +extern int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) __weak __ksym; > > +extern struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) __weak __ksym; > > +extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym; > > + > > #endif > > diff --git a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c > > index dc740bd0e2bd..6c2b0c3dbcd8 100644 > > --- a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c > > +++ b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c > > @@ -219,14 +219,52 @@ static void subtest_dmabuf_iter_check_default_iter(struct dmabuf_iter *skel) > > close(iter_fd); > > } > > > > +static void subtest_dmabuf_iter_check_open_coded(struct dmabuf_iter *skel, int map_fd) > > +{ > > + LIBBPF_OPTS(bpf_test_run_opts, topts); > > + char key[DMA_BUF_NAME_LEN]; > > + int err, fd; > > + bool found; > > + > > + /* No need to attach it, just run it directly */ > > + fd = bpf_program__fd(skel->progs.iter_dmabuf_for_each); > > + > > + err = bpf_prog_test_run_opts(fd, &topts); > > + if (!ASSERT_OK(err, "test_run_opts err")) > > + return; > > + if (!ASSERT_OK(topts.retval, "test_run_opts retval")) > > + return; > > + > > + if (!ASSERT_OK(bpf_map_get_next_key(map_fd, NULL, key), "get next key")) > > + return; > > + > > + do { > > + ASSERT_OK(bpf_map_lookup_elem(map_fd, key, &found), "lookup"); > > + ASSERT_TRUE(found, "found test buffer"); > > This check failed once in the CI, on s390: > > Error: #89/3 dmabuf_iter/open_coded > 9309 subtest_dmabuf_iter_check_open_coded:PASS:test_run_opts err 0 nsec > 9310 subtest_dmabuf_iter_check_open_coded:PASS:test_run_opts retval 0 nsec > 9311 subtest_dmabuf_iter_check_open_coded:PASS:get next key 0 nsec > 9312 subtest_dmabuf_iter_check_open_coded:PASS:lookup 0 nsec > 9313 subtest_dmabuf_iter_check_open_coded:FAIL:found test buffer > unexpected found test buffer: got FALSE > > But it passed in the rerun. It is probably a bit flakey. Maybe we need some > barrier somewhere. > > Here is the failure: > > https://github.com/kernel-patches/bpf/actions/runs/15002058808/job/42234864… > > To see the log, you need to log in GitHub. > > Thanks, > Song Thanks, yeah I have been trying to run this locally today but still working on setting up an environment for it. Daniel Xu thoughtfully suggested I use a github PR to trigger CI, but I tried that last week without success: https://github.com/kernel-patches/bpf/pull/8910 I'm not sure if this is the cause (doesn't show up on the runs that pass) but I have no idea why that would be intermittently failing: libbpf: Error in bpf_create_map_xattr(testbuf_hash): -EINVAL. Retrying without BTF. > > + } while (bpf_map_get_next_key(map_fd, key, key)); > > +} > > [...]

6 days, 19 hours

Re: [PATCH bpf-next v6 4/5] selftests/bpf: Add test for dmabuf_iter

by T.J. Mercier

On Wed, May 14, 2025 at 1:53 PM Song Liu <song(a)kernel.org> wrote: > > On Tue, May 13, 2025 at 9:36 AM T.J. Mercier <tjmercier(a)google.com> wrote: > > > > This test creates a udmabuf, and a dmabuf from the system dmabuf heap, > > and uses a BPF program that prints dmabuf metadata with the new > > dmabuf_iter to verify they can be found. > > > > Signed-off-by: T.J. Mercier <tjmercier(a)google.com> > > Acked-by: Christian König <christian.koenig(a)amd.com> > > Acked-by: Song Liu <song(a)kernel.org> Thanks. > > With one more comment below. > > [...] > > > diff --git a/tools/testing/selftests/bpf/progs/dmabuf_iter.c b/tools/testing/selftests/bpf/progs/dmabuf_iter.c > > new file mode 100644 > > index 000000000000..2a1b5397196d > > --- /dev/null > > +++ b/tools/testing/selftests/bpf/progs/dmabuf_iter.c > > @@ -0,0 +1,53 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +/* Copyright (c) 2025 Google LLC */ > > +#include <vmlinux.h> > > +#include <bpf/bpf_core_read.h> > > +#include <bpf/bpf_helpers.h> > > + > > +/* From uapi/linux/dma-buf.h */ > > +#define DMA_BUF_NAME_LEN 32 > > + > > +char _license[] SEC("license") = "GPL"; > > + > > +/* > > + * Fields output by this iterator are delimited by newlines. Convert any > > + * newlines in user-provided printed strings to spaces. > > + */ > > +static void sanitize_string(char *src, size_t size) > > +{ > > + for (char *c = src; *c && (size_t)(c - src) < size; ++c) > > We should do the size check first, right? IOW: > > for (char *c = src; (size_t)(c - src) < size && *c; ++c) Yeah if you call the function with size = 0, which is kinda questionable and not possible with the non-zero array size that is tied to immutable UAPI. Let's change it like you suggest. > > > + if (*c == '\n') > > + *c = ' '; > > +} > > + > [...]

6 days, 19 hours

[PATCH v4 00/40] drm/msm: sparse / "VM_BIND" support

by Rob Clark

From: Rob Clark <robdclark(a)chromium.org> Conversion to DRM GPU VA Manager[1], and adding support for Vulkan Sparse Memory[2] in the form of: 1. A new VM_BIND submitqueue type for executing VM MSM_SUBMIT_BO_OP_MAP/ MAP_NULL/UNMAP commands 2. A new VM_BIND ioctl to allow submitting batches of one or more MAP/MAP_NULL/UNMAP commands to a VM_BIND submitqueue I did not implement support for synchronous VM_BIND commands. Since userspace could just immediately wait for the `SUBMIT` to complete, I don't think we need this extra complexity in the kernel. Synchronous/immediate VM_BIND operations could be implemented with a 2nd VM_BIND submitqueue. The corresponding mesa MR: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32533 Changes in v4: - Various locking/etc fixes - Optimize the pgtable preallocation. If userspace sorts the VM_BIND ops then the kernel detects ops that fall into the same 2MB last level PTD to avoid duplicate page preallocation. - Add way to throttle pushing jobs to the scheduler, to cap the amount of potentially temporary prealloc'd pgtable pages. - Add vm_log to devcoredump for debugging. If the vm_log_shift module param is set, keep a log of the last 1<<vm_log_shift VM updates for easier debugging of faults/crashes. - Link to v3: https://lore.kernel.org/all/20250428205619.227835-1-robdclark@gmail.com/ Changes in v3: - Switched to seperate VM_BIND ioctl. This makes the UABI a bit cleaner, but OTOH the userspace code was cleaner when the end result of either type of VkQueue lead to the same ioctl. So I'm a bit on the fence. - Switched to doing the gpuvm bookkeeping synchronously, and only deferring the pgtable updates. This avoids needing to hold any resv locks in the fence signaling path, resolving the last shrinker related lockdep complaints. OTOH it means userspace can trigger invalid pgtable updates with multiple VM_BIND queues. In this case, we ensure that unmaps happen completely (to prevent userspace from using this to access free'd pages), mark the context as unusable, and move on with life. - Link to v2: https://lore.kernel.org/all/20250319145425.51935-1-robdclark@gmail.com/ Changes in v2: - Dropped Bibek Kumar Patro's arm-smmu patches[3], which have since been merged. - Pre-allocate all the things, and drop HACK patch which disabled shrinker. This includes ensuring that vm_bo objects are allocated up front, pre- allocating VMA objects, and pre-allocating pages used for pgtable updates. The latter utilizes io_pgtable_cfg callbacks for pgtable alloc/free, that were initially added for panthor. - Add back support for BO dumping for devcoredump. - Link to v1 (RFC): https://lore.kernel.org/dri-devel/20241207161651.410556-1-robdclark@gmail.c… [1] https://www.kernel.org/doc/html/next/gpu/drm-mm.html#drm-gpuvm [2] https://docs.vulkan.org/spec/latest/chapters/sparsemem.html [3] https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=909700 Rob Clark (40): drm/gpuvm: Don't require obj lock in destructor path drm/gpuvm: Allow VAs to hold soft reference to BOs drm/gem: Add ww_acquire_ctx support to drm_gem_lru_scan() drm/sched: Add enqueue credit limit iommu/io-pgtable-arm: Add quirk to quiet WARN_ON() drm/msm: Rename msm_file_private -> msm_context drm/msm: Improve msm_context comments drm/msm: Rename msm_gem_address_space -> msm_gem_vm drm/msm: Remove vram carveout support drm/msm: Collapse vma allocation and initialization drm/msm: Collapse vma close and delete drm/msm: Don't close VMAs on purge drm/msm: drm_gpuvm conversion drm/msm: Convert vm locking drm/msm: Use drm_gpuvm types more drm/msm: Split out helper to get iommu prot flags drm/msm: Add mmu support for non-zero offset drm/msm: Add PRR support drm/msm: Rename msm_gem_vma_purge() -> _unmap() drm/msm: Drop queued submits on lastclose() drm/msm: Lazily create context VM drm/msm: Add opt-in for VM_BIND drm/msm: Mark VM as unusable on GPU hangs drm/msm: Add _NO_SHARE flag drm/msm: Crashdump prep for sparse mappings drm/msm: rd dumping prep for sparse mappings drm/msm: Crashdec support for sparse drm/msm: rd dumping support for sparse drm/msm: Extract out syncobj helpers drm/msm: Use DMA_RESV_USAGE_BOOKKEEP/KERNEL drm/msm: Add VM_BIND submitqueue drm/msm: Support IO_PGTABLE_QUIRK_NO_WARN_ON drm/msm: Support pgtable preallocation drm/msm: Split out map/unmap ops drm/msm: Add VM_BIND ioctl drm/msm: Add VM logging for VM_BIND updates drm/msm: Add VMA unmap reason drm/msm: Add mmu prealloc tracepoint drm/msm: use trylock for debugfs drm/msm: Bump UAPI version drivers/gpu/drm/drm_gem.c | 14 +- drivers/gpu/drm/drm_gpuvm.c | 15 +- drivers/gpu/drm/msm/Kconfig | 1 + drivers/gpu/drm/msm/Makefile | 1 + drivers/gpu/drm/msm/adreno/a2xx_gpu.c | 25 +- drivers/gpu/drm/msm/adreno/a2xx_gpummu.c | 5 +- drivers/gpu/drm/msm/adreno/a3xx_gpu.c | 17 +- drivers/gpu/drm/msm/adreno/a4xx_gpu.c | 17 +- drivers/gpu/drm/msm/adreno/a5xx_debugfs.c | 4 +- drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 22 +- drivers/gpu/drm/msm/adreno/a5xx_power.c | 2 +- drivers/gpu/drm/msm/adreno/a5xx_preempt.c | 10 +- drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 32 +- drivers/gpu/drm/msm/adreno/a6xx_gmu.h | 2 +- drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 49 +- drivers/gpu/drm/msm/adreno/a6xx_gpu_state.c | 6 +- drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 10 +- drivers/gpu/drm/msm/adreno/adreno_device.c | 4 - drivers/gpu/drm/msm/adreno/adreno_gpu.c | 99 +- drivers/gpu/drm/msm/adreno/adreno_gpu.h | 23 +- .../drm/msm/disp/dpu1/dpu_encoder_phys_wb.c | 14 +- drivers/gpu/drm/msm/disp/dpu1/dpu_formats.c | 18 +- drivers/gpu/drm/msm/disp/dpu1/dpu_formats.h | 2 +- drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c | 18 +- drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c | 14 +- drivers/gpu/drm/msm/disp/dpu1/dpu_plane.h | 4 +- drivers/gpu/drm/msm/disp/mdp4/mdp4_crtc.c | 6 +- drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c | 28 +- drivers/gpu/drm/msm/disp/mdp4/mdp4_plane.c | 12 +- drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c | 4 +- drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c | 19 +- drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 12 +- drivers/gpu/drm/msm/dsi/dsi_host.c | 14 +- drivers/gpu/drm/msm/msm_drv.c | 184 +-- drivers/gpu/drm/msm/msm_drv.h | 35 +- drivers/gpu/drm/msm/msm_fb.c | 18 +- drivers/gpu/drm/msm/msm_fbdev.c | 2 +- drivers/gpu/drm/msm/msm_gem.c | 494 +++--- drivers/gpu/drm/msm/msm_gem.h | 247 ++- drivers/gpu/drm/msm/msm_gem_prime.c | 15 + drivers/gpu/drm/msm/msm_gem_shrinker.c | 104 +- drivers/gpu/drm/msm/msm_gem_submit.c | 295 ++-- drivers/gpu/drm/msm/msm_gem_vma.c | 1471 ++++++++++++++++- drivers/gpu/drm/msm/msm_gpu.c | 214 ++- drivers/gpu/drm/msm/msm_gpu.h | 144 +- drivers/gpu/drm/msm/msm_gpu_trace.h | 14 + drivers/gpu/drm/msm/msm_iommu.c | 302 +++- drivers/gpu/drm/msm/msm_kms.c | 18 +- drivers/gpu/drm/msm/msm_kms.h | 2 +- drivers/gpu/drm/msm/msm_mmu.h | 38 +- drivers/gpu/drm/msm/msm_rd.c | 62 +- drivers/gpu/drm/msm/msm_ringbuffer.c | 10 +- drivers/gpu/drm/msm/msm_submitqueue.c | 96 +- drivers/gpu/drm/msm/msm_syncobj.c | 172 ++ drivers/gpu/drm/msm/msm_syncobj.h | 37 + drivers/gpu/drm/scheduler/sched_entity.c | 16 +- drivers/gpu/drm/scheduler/sched_main.c | 3 + drivers/iommu/io-pgtable-arm.c | 27 +- include/drm/drm_gem.h | 10 +- include/drm/drm_gpuvm.h | 12 +- include/drm/gpu_scheduler.h | 13 +- include/linux/io-pgtable.h | 8 + include/uapi/drm/msm_drm.h | 149 +- 63 files changed, 3484 insertions(+), 1251 deletions(-) create mode 100644 drivers/gpu/drm/msm/msm_syncobj.c create mode 100644 drivers/gpu/drm/msm/msm_syncobj.h -- 2.49.0

6 days, 23 hours

[PATCH v4 00/40] drm/msm: sparse / "VM_BIND" support

by Rob Clark

1 week

Re: [RFC PATCH 00/12] Private MMIO support for private assigned dev

by Jason Gunthorpe

On Wed, May 14, 2025 at 03:02:53PM +0800, Xu Yilun wrote: > > We have an awkward fit for what CCA people are doing to the various > > Linux APIs. Looking somewhat maximally across all the arches a "bind" > > for a CC vPCI device creation operation does: > > > > - Setup the CPU page tables for the VM to have access to the MMIO > > This is guest side thing, is it? Anything host need to opt-in? CPU hypervisor page tables. > > - Revoke hypervisor access to the MMIO > > VFIO could choose never to mmap MMIO, so in this case nothing to do? Yes, if you do it that way. > > - Setup the vIOMMU to understand the vPCI device > > - Take over control of some of the IOVA translation, at least for T=1, > > and route to the the vIOMMU > > - Register the vPCI with any attestation functions the VM might use > > - Do some DOE stuff to manage/validate TDSIP/etc > > Intel TDX Connect has a extra requirement for "unbind": > > - Revoke KVM page table (S-EPT) for the MMIO only after TDISP > CONFIG_UNLOCK Maybe you could express this as the S-EPT always has the MMIO mapped into it as long as the vPCI function is installed to the VM? Is KVM responsible for the S-EPT? > Another thing is, seems your term "bind" includes all steps for > shared -> private conversion. Well, I was talking about vPCI creation. I understand that during the vPCI lifecycle the VM will do "bind" "unbind" which are more or less switching the device into a T=1 mode. Though I understood on some arches this was mostly invisible to the hypervisor? > But in my mind, "bind" only includes > putting device in TDISP LOCK state & corresponding host setups required > by firmware. I.e "bind" means host lockes down the CC setup, waiting for > guest attestation. So we will need to have some other API for this that modifies the vPCI object. It might be reasonable to have VFIO reach into iommufd to do that on an already existing iommufd VDEVICE object. A little weird, but we could probably make that work. But you have some weird ordering issues here if the S-EPT has to have the VFIO MMIO then you have to have a close() destruction order that sees VFIO remove the S-EPT and release the KVM, then have iommufd destroy the VDEVICE object. > > It doesn't mean that iommufd is suddenly doing PCI stuff, no, that > > stays in VFIO. > > I'm not sure if Alexey's patch [1] illustates your idea. It calls > tsm_tdi_bind() which directly does device stuff, and impacts MMIO. > VFIO doesn't know about this. > > I have to interpret this as VFIO firstly hand over device CC features > and MMIO resources to IOMMUFD, so VFIO never cares about them. > > [1] https://lore.kernel.org/all/20250218111017.491719-15-aik@amd.com/ There is also the PCI layer involved here and maybe PCI should be participating in managing some of this. Like it makes a bit of sense that PCI would block the FLR on platforms that require this? Jason

1 week

Re: [RFC v2 10/13] dma-fence: Add safe access helpers and document the rules

by Rob Clark

On Wed, May 14, 2025 at 7:58 AM Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> wrote: > > > On 14/05/2025 14:57, Rob Clark wrote: > > On Wed, May 14, 2025 at 3:01 AM Tvrtko Ursulin > > <tvrtko.ursulin(a)igalia.com> wrote: > >> > >> > >> On 13/05/2025 15:16, Rob Clark wrote: > >>> On Fri, May 9, 2025 at 8:34 AM Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> wrote: > >>>> > >>>> Dma-fence objects currently suffer from a potential use after free problem > >>>> where fences exported to userspace and other drivers can outlive the > >>>> exporting driver, or the associated data structures. > >>>> > >>>> The discussion on how to address this concluded that adding reference > >>>> counting to all the involved objects is not desirable, since it would need > >>>> to be very wide reaching and could cause unloadable drivers if another > >>>> entity would be holding onto a signaled fence reference potentially > >>>> indefinitely. > >>>> > >>>> This patch enables the safe access by introducing and documenting a > >>>> contract between fence exporters and users. It documents a set of > >>>> contraints and adds helpers which a) drivers with potential to suffer from > >>>> the use after free must use and b) users of the dma-fence API must use as > >>>> well. > >>>> > >>>> Premise of the design has multiple sides: > >>>> > >>>> 1. Drivers (fence exporters) MUST ensure a RCU grace period between > >>>> signalling a fence and freeing the driver private data associated with it. > >>>> > >>>> The grace period does not have to follow the signalling immediately but > >>>> HAS to happen before data is freed. > >>>> > >>>> 2. Users of the dma-fence API marked with such requirement MUST contain > >>>> the complete access to the data within a single code block guarded by the > >>>> new dma_fence_access_begin() and dma_fence_access_end() helpers. > >>>> > >>>> The combination of the two ensures that whoever sees the > >>>> DMA_FENCE_FLAG_SIGNALED_BIT not set is guaranteed to have access to a > >>>> valid fence->lock and valid data potentially accessed by the fence->ops > >>>> virtual functions, until the call to dma_fence_access_end(). > >>>> > >>>> 3. Module unload (fence->ops) disappearing is for now explicitly not > >>>> handled. That would required a more complex protection, possibly needing > >>>> SRCU instead of RCU to handle callers such as dma_fence_wait_timeout(), > >>>> where race between dma_fence_enable_sw_signaling, signalling, and > >>>> dereference of fence->ops->wait() would need a sleeping SRCU context. > >>>> > >>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> > >>>> --- > >>>> drivers/dma-buf/dma-fence.c | 69 +++++++++++++++++++++++++++++++++++++ > >>>> include/linux/dma-fence.h | 32 ++++++++++++----- > >>>> 2 files changed, 93 insertions(+), 8 deletions(-) > >>>> > >>>> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > >>>> index dc2456f68685..cfe1d7b79c22 100644 > >>>> --- a/drivers/dma-buf/dma-fence.c > >>>> +++ b/drivers/dma-buf/dma-fence.c > >>>> @@ -533,6 +533,7 @@ void dma_fence_release(struct kref *kref) > >>>> struct dma_fence *fence = > >>>> container_of(kref, struct dma_fence, refcount); > >>>> > >>>> + dma_fence_access_begin(); > >>>> trace_dma_fence_destroy(fence); > >>>> > >>>> if (WARN(!list_empty(&fence->cb_list) && > >>>> @@ -560,6 +561,8 @@ void dma_fence_release(struct kref *kref) > >>>> fence->ops->release(fence); > >>>> else > >>>> dma_fence_free(fence); > >>>> + > >>>> + dma_fence_access_end(); > >>>> } > >>>> EXPORT_SYMBOL(dma_fence_release); > >>>> > >>>> @@ -982,11 +985,13 @@ EXPORT_SYMBOL(dma_fence_set_deadline); > >>>> */ > >>>> void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq) > >>>> { > >>>> + dma_fence_access_begin(); > >>>> seq_printf(seq, "%s %s seq %llu %ssignalled\n", > >>>> dma_fence_driver_name(fence), > >>>> dma_fence_timeline_name(fence), > >>>> fence->seqno, > >>>> dma_fence_is_signaled(fence) ? "" : "un"); > >>>> + dma_fence_access_end(); > >>>> } > >>>> EXPORT_SYMBOL(dma_fence_describe); > >>>> > >>>> @@ -1033,3 +1038,67 @@ dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops, > >>>> __set_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags); > >>>> } > >>>> EXPORT_SYMBOL(dma_fence_init64); > >>>> + > >>>> +/** > >>>> + * dma_fence_driver_name - Access the driver name > >>>> + * @fence: the fence to query > >>>> + * > >>>> + * Returns a driver name backing the dma-fence implementation. > >>>> + * > >>>> + * IMPORTANT CONSIDERATION: > >>>> + * Dma-fence contract stipulates that access to driver provided data (data not > >>>> + * directly embedded into the object itself), such as the &dma_fence.lock and > >>>> + * memory potentially accessed by the &dma_fence.ops functions, is forbidden > >>>> + * after the fence has been signalled. Drivers are allowed to free that data, > >>>> + * and some do. > >>>> + * > >>>> + * To allow safe access drivers are mandated to guarantee a RCU grace period > >>>> + * between signalling the fence and freeing said data. > >>>> + * > >>>> + * As such access to the driver name is only valid inside a RCU locked section. > >>>> + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded > >>>> + * by the &dma_fence_access_being and &dma_fence_access_end pair. > >>>> + */ > >>>> +const char *dma_fence_driver_name(struct dma_fence *fence) > >>>> +{ > >>>> + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), > >>>> + "rcu_read_lock() required for safe access to returned string"); > >>>> + > >>>> + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) > >>>> + return fence->ops->get_driver_name(fence); > >>>> + else > >>>> + return "detached-driver"; > >>>> +} > >>>> +EXPORT_SYMBOL(dma_fence_driver_name); > >>>> + > >>>> +/** > >>>> + * dma_fence_timeline_name - Access the timeline name > >>>> + * @fence: the fence to query > >>>> + * > >>>> + * Returns a timeline name provided by the dma-fence implementation. > >>>> + * > >>>> + * IMPORTANT CONSIDERATION: > >>>> + * Dma-fence contract stipulates that access to driver provided data (data not > >>>> + * directly embedded into the object itself), such as the &dma_fence.lock and > >>>> + * memory potentially accessed by the &dma_fence.ops functions, is forbidden > >>>> + * after the fence has been signalled. Drivers are allowed to free that data, > >>>> + * and some do. > >>>> + * > >>>> + * To allow safe access drivers are mandated to guarantee a RCU grace period > >>>> + * between signalling the fence and freeing said data. > >>>> + * > >>>> + * As such access to the driver name is only valid inside a RCU locked section. > >>>> + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded > >>>> + * by the &dma_fence_access_being and &dma_fence_access_end pair. > >>>> + */ > >>>> +const char *dma_fence_timeline_name(struct dma_fence *fence) > >>>> +{ > >>>> + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), > >>>> + "rcu_read_lock() required for safe access to returned string"); > >>>> + > >>>> + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) > >>>> + return fence->ops->get_driver_name(fence); > >>>> + else > >>>> + return "signaled-timeline"; > >>> > >>> This means that trace_dma_fence_signaled() will get the wrong > >>> timeline/driver name, which probably screws up perfetto and maybe > >>> other tools. > >> > >> Do you think context and seqno are not enough for those tools and they > >> actually rely on the names? It would sound weird if they decided to > >> index anything on the names which are non-standardised between drivers, > >> but I guess anything is possible. > > > > At some point perfetto uses the timeline name to put up a named fence > > timeline, I'm not sure if it is using the name or context # for > > subsequent fence events (namely, signalled). I'd have to check the > > code and get back to you. > > If you can it would be useful. Presumably it saves the names from the > start edge of fence lifetime. But again, who knows. Ok, it looks like perfetto is ok... mostly.. DrmTracker::GetFenceTimelineByContext() will try to lookup the timeline by context #, and then if that fails, create a new timeline with the name from the trace event, and add it to the hashmap. It might be that "signaled-timeline" shows up if the first event seen is the fence-signaled event. > > There is also gpuvis, which I guess does something similar, but > > haven't looked into it. Idk if there are others. > > I know GpuVis uses DRM sched tracepoints since Pierre-Eric was > explaining me about those in the context of tracing rework he did there. > I am not sure about dma-fence tracepoints. > > +Pierre-Eric on the off chance you know from the top of your head how > much GpuVis depends on them (dma-fence tracepoints). > > >>> Maybe it would work well enough just to move the > >>> trace_dma_fence_signaled() call ahead of the test_and_set_bit()? Idk > >>> if some things will start getting confused if they see that trace > >>> multiple times. > >> > >> Another alternative is to make this tracepoint access the names > >> directly. It is under the lock so guaranteed not to get freed with > >> drivers which will be made compliant with the documented rules. > > > > I guess it would have been better if, other than dma_fence_init > > tracepoint, later tracepoints didn't include the driver/timeline > > name.. that would have forced the use of the context. But I guess too > > late for that. Perhaps the least bad thing to do is use the locking? > > You mean this last alternative I mentioned? I think that will work fine. > I'll wait a little bit longer for more potential comments before re-spi > ning with that. yes > Were you able to test the series for your use case? Assuming it is not > upstream msm since I don't immediately see a path in msm_fence which > gets freed at runtime? Not yet, but I think it should because it is the exact same problem your igt test triggers. This is with my VM_BIND series, which will dynamically create/teardown sched entities BR, -R

1 week

Re: [RFC v2 10/13] dma-fence: Add safe access helpers and document the rules

by Rob Clark

On Wed, May 14, 2025 at 3:01 AM Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> wrote: > > > On 13/05/2025 15:16, Rob Clark wrote: > > On Fri, May 9, 2025 at 8:34 AM Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> wrote: > >> > >> Dma-fence objects currently suffer from a potential use after free problem > >> where fences exported to userspace and other drivers can outlive the > >> exporting driver, or the associated data structures. > >> > >> The discussion on how to address this concluded that adding reference > >> counting to all the involved objects is not desirable, since it would need > >> to be very wide reaching and could cause unloadable drivers if another > >> entity would be holding onto a signaled fence reference potentially > >> indefinitely. > >> > >> This patch enables the safe access by introducing and documenting a > >> contract between fence exporters and users. It documents a set of > >> contraints and adds helpers which a) drivers with potential to suffer from > >> the use after free must use and b) users of the dma-fence API must use as > >> well. > >> > >> Premise of the design has multiple sides: > >> > >> 1. Drivers (fence exporters) MUST ensure a RCU grace period between > >> signalling a fence and freeing the driver private data associated with it. > >> > >> The grace period does not have to follow the signalling immediately but > >> HAS to happen before data is freed. > >> > >> 2. Users of the dma-fence API marked with such requirement MUST contain > >> the complete access to the data within a single code block guarded by the > >> new dma_fence_access_begin() and dma_fence_access_end() helpers. > >> > >> The combination of the two ensures that whoever sees the > >> DMA_FENCE_FLAG_SIGNALED_BIT not set is guaranteed to have access to a > >> valid fence->lock and valid data potentially accessed by the fence->ops > >> virtual functions, until the call to dma_fence_access_end(). > >> > >> 3. Module unload (fence->ops) disappearing is for now explicitly not > >> handled. That would required a more complex protection, possibly needing > >> SRCU instead of RCU to handle callers such as dma_fence_wait_timeout(), > >> where race between dma_fence_enable_sw_signaling, signalling, and > >> dereference of fence->ops->wait() would need a sleeping SRCU context. > >> > >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> > >> --- > >> drivers/dma-buf/dma-fence.c | 69 +++++++++++++++++++++++++++++++++++++ > >> include/linux/dma-fence.h | 32 ++++++++++++----- > >> 2 files changed, 93 insertions(+), 8 deletions(-) > >> > >> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > >> index dc2456f68685..cfe1d7b79c22 100644 > >> --- a/drivers/dma-buf/dma-fence.c > >> +++ b/drivers/dma-buf/dma-fence.c > >> @@ -533,6 +533,7 @@ void dma_fence_release(struct kref *kref) > >> struct dma_fence *fence = > >> container_of(kref, struct dma_fence, refcount); > >> > >> + dma_fence_access_begin(); > >> trace_dma_fence_destroy(fence); > >> > >> if (WARN(!list_empty(&fence->cb_list) && > >> @@ -560,6 +561,8 @@ void dma_fence_release(struct kref *kref) > >> fence->ops->release(fence); > >> else > >> dma_fence_free(fence); > >> + > >> + dma_fence_access_end(); > >> } > >> EXPORT_SYMBOL(dma_fence_release); > >> > >> @@ -982,11 +985,13 @@ EXPORT_SYMBOL(dma_fence_set_deadline); > >> */ > >> void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq) > >> { > >> + dma_fence_access_begin(); > >> seq_printf(seq, "%s %s seq %llu %ssignalled\n", > >> dma_fence_driver_name(fence), > >> dma_fence_timeline_name(fence), > >> fence->seqno, > >> dma_fence_is_signaled(fence) ? "" : "un"); > >> + dma_fence_access_end(); > >> } > >> EXPORT_SYMBOL(dma_fence_describe); > >> > >> @@ -1033,3 +1038,67 @@ dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops, > >> __set_bit(DMA_FENCE_FLAG_SEQNO64_BIT, &fence->flags); > >> } > >> EXPORT_SYMBOL(dma_fence_init64); > >> + > >> +/** > >> + * dma_fence_driver_name - Access the driver name > >> + * @fence: the fence to query > >> + * > >> + * Returns a driver name backing the dma-fence implementation. > >> + * > >> + * IMPORTANT CONSIDERATION: > >> + * Dma-fence contract stipulates that access to driver provided data (data not > >> + * directly embedded into the object itself), such as the &dma_fence.lock and > >> + * memory potentially accessed by the &dma_fence.ops functions, is forbidden > >> + * after the fence has been signalled. Drivers are allowed to free that data, > >> + * and some do. > >> + * > >> + * To allow safe access drivers are mandated to guarantee a RCU grace period > >> + * between signalling the fence and freeing said data. > >> + * > >> + * As such access to the driver name is only valid inside a RCU locked section. > >> + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded > >> + * by the &dma_fence_access_being and &dma_fence_access_end pair. > >> + */ > >> +const char *dma_fence_driver_name(struct dma_fence *fence) > >> +{ > >> + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), > >> + "rcu_read_lock() required for safe access to returned string"); > >> + > >> + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) > >> + return fence->ops->get_driver_name(fence); > >> + else > >> + return "detached-driver"; > >> +} > >> +EXPORT_SYMBOL(dma_fence_driver_name); > >> + > >> +/** > >> + * dma_fence_timeline_name - Access the timeline name > >> + * @fence: the fence to query > >> + * > >> + * Returns a timeline name provided by the dma-fence implementation. > >> + * > >> + * IMPORTANT CONSIDERATION: > >> + * Dma-fence contract stipulates that access to driver provided data (data not > >> + * directly embedded into the object itself), such as the &dma_fence.lock and > >> + * memory potentially accessed by the &dma_fence.ops functions, is forbidden > >> + * after the fence has been signalled. Drivers are allowed to free that data, > >> + * and some do. > >> + * > >> + * To allow safe access drivers are mandated to guarantee a RCU grace period > >> + * between signalling the fence and freeing said data. > >> + * > >> + * As such access to the driver name is only valid inside a RCU locked section. > >> + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded > >> + * by the &dma_fence_access_being and &dma_fence_access_end pair. > >> + */ > >> +const char *dma_fence_timeline_name(struct dma_fence *fence) > >> +{ > >> + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), > >> + "rcu_read_lock() required for safe access to returned string"); > >> + > >> + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) > >> + return fence->ops->get_driver_name(fence); > >> + else > >> + return "signaled-timeline"; > > > > This means that trace_dma_fence_signaled() will get the wrong > > timeline/driver name, which probably screws up perfetto and maybe > > other tools. > > Do you think context and seqno are not enough for those tools and they > actually rely on the names? It would sound weird if they decided to > index anything on the names which are non-standardised between drivers, > but I guess anything is possible. At some point perfetto uses the timeline name to put up a named fence timeline, I'm not sure if it is using the name or context # for subsequent fence events (namely, signalled). I'd have to check the code and get back to you. There is also gpuvis, which I guess does something similar, but haven't looked into it. Idk if there are others. > > Maybe it would work well enough just to move the > > trace_dma_fence_signaled() call ahead of the test_and_set_bit()? Idk > > if some things will start getting confused if they see that trace > > multiple times. > > Another alternative is to make this tracepoint access the names > directly. It is under the lock so guaranteed not to get freed with > drivers which will be made compliant with the documented rules. I guess it would have been better if, other than dma_fence_init tracepoint, later tracepoints didn't include the driver/timeline name.. that would have forced the use of the context. But I guess too late for that. Perhaps the least bad thing to do is use the locking? BR, -R

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Linaro-mm-sig May 2025