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@xxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Rob Herring <robh@xxxxxxxxxx>
Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
Cc: Eric Anholt <eric@xxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: "VMware Graphics" <linux-graphics-maintainer@xxxxxxxxxx>
Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
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);
--
2.23.0.rc1
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