Linaro-mm-sig

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7054 discussions

[PATCH v3 05/11] dma-buf: Use trace_call__##name() at guarded tracepoint call sites

by Vineeth Pillai (Google)

From: Vineeth Pillai <vineeth(a)bitbyteword.org> Replace trace_foo() with the new trace_call__foo() at sites already guarded by trace_foo_enabled(), avoiding a redundant static_branch_unlikely() re-evaluation inside the tracepoint. trace_call__foo() calls the tracepoint callbacks directly without utilizing the static branch again. Original v2 series: https://lore.kernel.org/linux-trace-kernel/20260323160052.17528-1-vineeth@b… Parts of the original v2 series have already been merged in mainline. This patch is being reposted as a follow-up cleanup for the remaining unmerged pieces. Suggested-by: Steven Rostedt <rostedt(a)goodmis.org> Suggested-by: Peter Zijlstra <peterz(a)infradead.org> Signed-off-by: Vineeth Pillai (Google) <vineeth(a)bitbyteword.org> Assisted-by: Claude:claude-sonnet-4-6 --- drivers/dma-buf/dma-fence.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index a2aa82f4eedd..a41cdd9c9343 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -553,7 +553,7 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout) } if (trace_dma_fence_wait_end_enabled()) { rcu_read_lock(); - trace_dma_fence_wait_end(fence); + trace_call__dma_fence_wait_end(fence); rcu_read_unlock(); } return ret; -- 2.54.0

3 months

[PATCH v2] drm/virtio: move cursor resv lock acquisition to prepare_fb

by Deepanshu Kartikey

virtio_gpu_cursor_plane_update() allocates a virtio_gpu_object_array, locks its dma_resv, and queues a fenced transfer to the host. The lock acquisition can fail in two ways: - dma_resv_lock_interruptible() returns -EINTR when a signal is delivered while waiting for the reservation lock. - dma_resv_reserve_fences() returns -ENOMEM if it fails to allocate a fence slot; in this case lock_resv unlocks before returning. The return value was ignored, so the cursor path could proceed with the resv lock not held. The queue path then walks the object array and calls dma_resv_add_fence(), which requires the lock; with lockdep enabled this trips dma_resv_assert_held(): WARNING: drivers/dma-buf/dma-resv.c:296 at dma_resv_add_fence+0x71e/0x840 Call Trace: virtio_gpu_array_add_fence virtio_gpu_queue_ctrl_sgs virtio_gpu_queue_fenced_ctrl_buffer virtio_gpu_cursor_plane_update drm_atomic_helper_commit_planes drm_atomic_helper_commit_tail commit_tail drm_atomic_helper_commit drm_atomic_commit drm_atomic_helper_update_plane __setplane_atomic drm_mode_cursor_universal drm_mode_cursor_common drm_mode_cursor_ioctl drm_ioctl __x64_sys_ioctl Beyond the WARN, mutating the dma_resv fence list without the lock races with concurrent readers/writers and can corrupt the list. The DRM atomic helpers do not allow .atomic_update to fail: by the time it runs, the commit has been signed off to userspace and there is no clean rollback path. Move the fallible work -- objs allocation, dma_resv locking, and fence slot reservation -- into virtio_gpu_plane_prepare_fb, which is the designated callback for resource acquisition and may return errors that the framework handles by rolling back the commit. Stash the prepared object array on virtio_gpu_plane_state so the update step can consume it. Make virtio_gpu_plane_cleanup_fb release the objs if the commit was rolled back before update ran (i.e., objs not consumed). The queue path already unlocks the resv after attaching the fence (vq.c:411) and frees the array via put_free_delayed after host completion (vq.c:271), so the update step only needs to clear vgplane_st->objs to transfer ownership. Simplify virtio_gpu_cursor_plane_update to a no-fail queue submission that hands the prepared, locked objs to the queue path. The bug was reported by syzbot, triggered via fault injection (fail_nth) on the DRM_IOCTL_MODE_CURSOR path, which forces the -ENOMEM branch in dma_resv_reserve_fences(). Reported-by: syzbot+72bd3dd3a5d5f39a0271(a)syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=72bd3dd3a5d5f39a0271 Fixes: 5cfd31c5b3a3 ("drm/virtio: fix virtio_gpu_cursor_plane_update().") Cc: stable(a)vger.kernel.org Link: https://lore.kernel.org/all/20260510053025.100224-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey <kartikey406(a)gmail.com> --- v2: Move resv lock acquisition from .atomic_update (which must not fail) to .prepare_fb (which may), per maintainer review of v1. The previous approach of silently skipping the cursor update on lock failure violated the atomic-commit contract with userspace. --- drivers/gpu/drm/virtio/virtgpu_drv.h | 1 + drivers/gpu/drm/virtio/virtgpu_plane.c | 38 ++++++++++++++++++++------ 2 files changed, 30 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h index f17660a71a3e..e51f959dce46 100644 --- a/drivers/gpu/drm/virtio/virtgpu_drv.h +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h @@ -198,6 +198,7 @@ struct virtio_gpu_framebuffer { struct virtio_gpu_plane_state { struct drm_plane_state base; struct virtio_gpu_fence *fence; + struct virtio_gpu_object_array *objs; }; #define to_virtio_gpu_plane_state(x) \ container_of(x, struct virtio_gpu_plane_state, base) diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c index a126d1b25f46..b0511ace89e6 100644 --- a/drivers/gpu/drm/virtio/virtgpu_plane.c +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c @@ -381,6 +381,23 @@ static int virtio_gpu_plane_prepare_fb(struct drm_plane *plane, goto err_fence; } + if (plane->type == DRM_PLANE_TYPE_CURSOR && bo->dumb) { + struct virtio_gpu_object_array *objs; + + objs = virtio_gpu_array_alloc(1); + if (!objs) { + ret = -ENOMEM; + goto err_fence; + } + virtio_gpu_array_add_obj(objs, vgfb->base.obj[0]); + ret = virtio_gpu_array_lock_resv(objs); + if (ret) { + virtio_gpu_array_put_free(objs); + goto err_fence; + } + vgplane_st->objs = objs; + } + return 0; err_fence: @@ -417,6 +434,12 @@ static void virtio_gpu_plane_cleanup_fb(struct drm_plane *plane, vgplane_st->fence = NULL; } + if (vgplane_st->objs) { + virtio_gpu_array_unlock_resv(vgplane_st->objs); + virtio_gpu_array_put_free(vgplane_st->objs); + vgplane_st->objs = NULL; + } + obj = state->fb->obj[0]; if (drm_gem_is_imported(obj)) virtio_gpu_cleanup_imported_obj(obj); @@ -452,21 +475,18 @@ static void virtio_gpu_cursor_plane_update(struct drm_plane *plane, } if (bo && bo->dumb && (plane->state->fb != old_state->fb)) { - /* new cursor -- update & wait */ - struct virtio_gpu_object_array *objs; - - objs = virtio_gpu_array_alloc(1); - if (!objs) - return; - virtio_gpu_array_add_obj(objs, vgfb->base.obj[0]); - virtio_gpu_array_lock_resv(objs); + /* objs and fence were prepared in virtio_gpu_plane_prepare_fb; + * the resv is already locked. The queue path takes ownership + * of objs and unlocks the resv after attaching the fence. + */ virtio_gpu_cmd_transfer_to_host_2d (vgdev, 0, plane->state->crtc_w, plane->state->crtc_h, - 0, 0, objs, vgplane_st->fence); + 0, 0, vgplane_st->objs, vgplane_st->fence); virtio_gpu_notify(vgdev); dma_fence_wait(&vgplane_st->fence->f, true); + vgplane_st->objs = NULL; } if (plane->state->fb != old_state->fb) { -- 2.43.0

3 months

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3 months, 1 week

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3 months, 1 week

Re: [PATCH v3 00/10] Add dmabuf read/write via io_uring

by Pavel Begunkov

On 5/7/26 10:50, Ming Lei wrote: ... >>> BTW, inspired by this approach, I adds similar feature to ublk via UBLK_IO_F_SHMEM_ZC >>> which can maintain long-term vfio dma mapping over registered user-place aligned buffer. >> >> Interesting, just too a glance, and it looks like what David Wei >> was thinking to add to fuse, but IIUC he gave up exactly because the >> client will need to cooperate and that could be troublesome. > > Here the cooperation is minimized, maybe one shmem/hugetlb path, or memfd, > and it is one optimization and opt-in, and fallback to normal path > if application doesn't cooperate. My point is that with widely enough adopted interface the user will be able to opportunistically use it without knowledge about the file, i.e. not knowing whether it's ublk or something else. But as you mentioned below, it'd be cooperative interface in either case. >> Should we try to push everything under the same interface instead of >> keeping a ublk specific one? Again to the point that it requires > > If generic interface can be figured out, it shouldn't be a big deal for > ublk to switch to it, and the usage is simple actually. Sure, you'd just need to maintain both as there is a mismatch between interfaces. > So far, ublk supports both FS and nvme block device. > > And cooperation can't be avoided for this usage no matter if generic or > driver specific implementation is taken, for both fuse & ublk. -- Pavel Begunkov

3 months, 1 week

Mastering the Quirky Fun of Drive Mad

by cold.puma.etfk＠hidingmail.net

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3 months, 1 week

Re: [RFC PATCH 04/12] vfio/pci: Allow MMIO regions to be exported through dma-buf

by Alexey Kardashevskiy

On 7/5/26 17:16, Alexey Kardashevskiy wrote: > On 6/5/26 23:16, Jason Gunthorpe wrote: >> On Wed, May 06, 2026 at 12:35:42PM +1000, Alexey Kardashevskiy wrote: >>> Hi! >>> >>> Let's reignite this topic. >>> >>> I've been using these patches + QEMU side hacks for 6+ months. And it's been fine until I got a device where MSIX BAR is in a middle of another BAR marked as TEE in the TDISP interface report. And no trusted MSIX yet. >>> >>> Every time QEMU mmaps a BAR - I request a dmabuf fd from VFIO in QEMU. Since mapping of an entire MSIX BAR is allowed by default, VFIORegion::nr_mmaps==1 and it is an entire BAR. >>> >>> Problem: KVM memslot mismatches the dmabuf fd size >> >> Huh? kvm does not care about dmabuf at all? Are you running other >> patches to hook kvm and dmabuf? > > yup, 06/12 of this patchset. > >> Putting a slice in a dmabuf is a well understood need for MSI, so I >> expect whatever kvm dmabuf interface that gets merged to accomodate >> this? > > good to know. > >>> Solution2: modify logic in VFIO dmabuf to allow multiple KVM memory >>> slots per dmabuf. Now it is kvm_memory_slot::dmabuf_attach with no >>> offset into the dmabuf and one kvm_vfio_dmabuf per dma_buf. >> >> Yes, when kvm learns to take in a dmabuf it needs to take in a slice, >> not the whole buf. Or you need to create multiple dmabufs with the >> necessary slices from the VFIO. The upstream vfio dmabuf creation >> allows creating it with a slice. > > true but either way dmabuf slicing will be directed by QEMU's msix-table emulation MR and this slicing needs to match the TDISP report so I'll have to teach QEMU these reports, right? Or TDISP devices are going to align MSIX BARs to 4K, and QEMU will do the same and it should "just work", and if it does not - the host won't crash. Can this work? Thanks, > I am worried if I miss something obvious, again. Thanks, > > > ps. I like nntp.lore.kernel.org very much for ability to dig out old stuff and then just reply to it :) > >> >> Jason > -- Alexey

3 months, 1 week

[PATCH] drm/virtio: check virtio_gpu_array_lock_resv() return in cursor update

by Deepanshu Kartikey

virtio_gpu_cursor_plane_update() calls virtio_gpu_array_lock_resv() but ignores its return value. The function can fail in two ways: - dma_resv_lock_interruptible() returns -ERESTARTSYS when a signal is delivered while waiting for the reservation lock. - dma_resv_reserve_fences() returns -ENOMEM if it fails to allocate a fence slot; in this case lock_resv unlocks before returning. In both cases the resv lock is not held on return. The cursor path proceeds to queue a fenced transfer command. The queue path then walks the object array and calls dma_resv_add_fence() on the cursor BO's reservation. dma_resv_add_fence() requires the resv lock to be held; with lockdep enabled the missing lock trips dma_resv_assert_held(): WARNING: drivers/dma-buf/dma-resv.c:296 at dma_resv_add_fence+0x71e/0x840 Call Trace: virtio_gpu_array_add_fence+0xcd/0x140 virtio_gpu_queue_ctrl_sgs virtio_gpu_queue_fenced_ctrl_buffer+0x578/0xfb0 virtio_gpu_cursor_plane_update+0x411/0xbc0 drm_atomic_helper_commit_planes+0x497/0xf10 ... drm_mode_cursor_ioctl+0xd4/0x110 drm_ioctl+0x5e6/0xc60 __x64_sys_ioctl+0x18e/0x210 Beyond the WARN, mutating the dma_resv fence list without the lock races with concurrent readers/writers and can corrupt the list. Check the return value of virtio_gpu_array_lock_resv(). On failure, drop the references taken by virtio_gpu_array_add_obj() with virtio_gpu_array_put_free() (which does not unlock, matching the not-locked state) and return without queueing the command. A skipped cursor frame is harmless; the WARN and the underlying race are not. The bug was reported by syzbot, triggered via fault injection (fail_nth) on the DRM_IOCTL_MODE_CURSOR path, which forces the -ENOMEM branch in dma_resv_reserve_fences(). Reported-by: syzbot+72bd3dd3a5d5f39a0271(a)syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=72bd3dd3a5d5f39a0271 Fixes: 5cfd31c5b3a3 ("drm/virtio: fix virtio_gpu_cursor_plane_update().") Cc: stable(a)vger.kernel.org Signed-off-by: Deepanshu Kartikey <kartikey406(a)gmail.com> --- drivers/gpu/drm/virtio/virtgpu_plane.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c index a126d1b25f46..ca379b08b9ec 100644 --- a/drivers/gpu/drm/virtio/virtgpu_plane.c +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c @@ -459,7 +459,10 @@ static void virtio_gpu_cursor_plane_update(struct drm_plane *plane, if (!objs) return; virtio_gpu_array_add_obj(objs, vgfb->base.obj[0]); - virtio_gpu_array_lock_resv(objs); + if (virtio_gpu_array_lock_resv(objs)) { + virtio_gpu_array_put_free(objs); + return; + } virtio_gpu_cmd_transfer_to_host_2d (vgdev, 0, plane->state->crtc_w, -- 2.43.0

3 months, 1 week

Re: [PATCH RFC 21/26] dma-buf: Add the Physical Address List DMA mapping type

by Jason Gunthorpe

On Sat, May 09, 2026 at 01:31:56PM +0800, Xu Yilun wrote: > > Would you be open to an in-between? The exporter and importer both > > have information that should not leak into each other's drivers. > > > > What if the dmabuf mapping type core code was the only thing that had > > access to *BOTH*? The exporter provides the address data, the importer > > provides the iommu_domain. The core code, and only the core code, has > > both and does the required operation? > > I think that may not work for KVM. On IOMMU side, IOMMUFD acts as the > address space (iova) manager and dma_api/IOMMU driver acts as the > actual page table mapper. But for KVM, it is both. KVM doesn't allow > another component to provide an unknown address space (GPA space) and > say "map it", so doesn't expose to other components about "KVM domain". > > Even if we expose "KVM domain", KVM still acts as the importer and the > mapper, is it wierd to say we trust KVM-the-mapper, but don't trust > KVM-the-as-manager? > > Is it also wierd that we trust IOMMU-the-mapper, but don't trust > IOMMUFD-the-as-manager? There are more IOMMU drivers than IOMMUFD... Yeah, it doesn't work well for kvm, and yes it is really weird and worse that phys in every way.. Jason

3 months, 1 week

Re: [RFC PATCH 04/12] vfio/pci: Allow MMIO regions to be exported through dma-buf

by Jason Gunthorpe

On Thu, May 07, 2026 at 05:16:56PM +1000, Alexey Kardashevskiy wrote: > true but either way dmabuf slicing will be directed by QEMU's > msix-table emulation MR and this slicing needs to match the TDISP > report so I'll have to teach QEMU these reports, right? I am worried > if I miss something obvious, again. Thanks, I don't think so.. It just needs to slice it into the MSI page blindly. When the VM goes to validate the TDISP report against the mappings it will fail to accept the device if there is a mismatch. The only thing qemu could do is fail sooner, but I don't know that is worth the complexity as we do expect all devices to have their MSI range unprotected. Jason

3 months, 1 week

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