Full audit of everyone:
- i915, radeon, amdgpu should be clean per their maintainers.
- vram helpers should be fine, they don't do command submission, so really no business holding struct_mutex while doing copy_*_user. But I haven't checked them all.
- panfrost seems to dma_resv_lock only in panfrost_job_push, which looks clean.
- v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(), copying from/to userspace happens all in v3d_lookup_bos which is outside of the critical section.
- vmwgfx has a bunch of ioctls that do their own copy_*_user: - vmw_execbuf_process: First this does some copies in vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself. Then comes the usual ttm reserve/validate sequence, then actual submission/fencing, then unreserving, and finally some more copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of details, but looks all safe. - vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be seen, seems to only create a fence and copy it out. - a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be found there. Summary: vmwgfx seems to be fine too.
- virtio: There's virtio_gpu_execbuffer_ioctl, which does all the copying from userspace before even looking up objects through their handles, so safe. Plus the getparam/getcaps ioctl, also both safe.
- qxl only has qxl_execbuffer_ioctl, which calls into qxl_process_single_command. There's a lovely comment before the __copy_from_user_inatomic that the slowpath should be copied from i915, but I guess that never happened. Try not to be unlucky and get your CS data evicted between when it's written and the kernel tries to read it. The only other copy_from_user is for relocs, but those are done before qxl_release_reserve_list(), which seems to be the only thing reserving buffers (in the ttm/dma_resv sense) in that code. So looks safe.
- A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this everywhere and needs to be fixed up.
v2: Thomas pointed at that vmwgfx calls dma_resv_init while it holds a dma_resv lock of a different object already. Christian mentioned that ttm core does this too for ghost objects. intel-gfx-ci highlighted that i915 has similar issues.
Unfortunately we can't do this in the usual module init functions, because kernel threads don't have an ->mm - we have to wait around for some user thread to do this.
Solution is to spawn a worker (but only once). It's horrible, but it works.
Cc: Alex Deucher alexander.deucher@amd.com Cc: Christian König christian.koenig@amd.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Rob Herring robh@kernel.org Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Eric Anholt eric@anholt.net Cc: Dave Airlie airlied@redhat.com Cc: Gerd Hoffmann kraxel@redhat.com Cc: Ben Skeggs bskeggs@redhat.com Cc: "VMware Graphics" linux-graphics-maintainer@vmware.com Cc: Thomas Hellstrom thellstrom@vmware.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com --- drivers/dma-buf/dma-resv.c | 42 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 42a8f3f11681..29988b1564c1 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -34,6 +34,7 @@
#include <linux/dma-resv.h> #include <linux/export.h> +#include <linux/sched/mm.h>
/** * DOC: Reservation Object Overview @@ -95,6 +96,28 @@ static void dma_resv_list_free(struct dma_resv_list *list) kfree_rcu(list, rcu); }
+#if IS_ENABLED(CONFIG_LOCKDEP) +struct lockdep_work { + struct work_struct work; + struct dma_resv obj; + struct mm_struct *mm; +} lockdep_work; + +void lockdep_work_fn(struct work_struct *work) +{ + dma_resv_init(&lockdep_work.obj); + + down_read(&lockdep_work.mm->mmap_sem); + ww_mutex_lock(&lockdep_work.obj.lock, NULL); + fs_reclaim_acquire(GFP_KERNEL); + fs_reclaim_release(GFP_KERNEL); + ww_mutex_unlock(&lockdep_work.obj.lock); + up_read(&lockdep_work.mm->mmap_sem); + + mmput(lockdep_work.mm); +} +#endif + /** * dma_resv_init - initialize a reservation object * @obj: the reservation object @@ -107,6 +130,25 @@ void dma_resv_init(struct dma_resv *obj) &reservation_seqcount_class); RCU_INIT_POINTER(obj->fence, NULL); RCU_INIT_POINTER(obj->fence_excl, NULL); + +#if IS_ENABLED(CONFIG_LOCKDEP) + if (current->mm) { + static atomic_t lockdep_primed; + + /* + * This gets called from all kinds of places, launch a worker. + * Usual init sections don't work for kernel threads lack an + * ->mm. + */ + if (atomic_cmpxchg(&lockdep_primed, 0, 1) == 0) { + INIT_WORK(&lockdep_work.work, lockdep_work_fn); + lockdep_work.mm = current->mm; + mmget(lockdep_work.mm); + + schedule_work(&lockdep_work.work); + } + } +#endif } EXPORT_SYMBOL(dma_resv_init);