On Mon, Jun 16, 2025 at 03:25:08PM -0700, Rob Clark wrote:
> On Mon, Jun 16, 2025 at 2:39 PM Danilo Krummrich <d...@redhat.com> wrote:
> >
> > On Sat, Jun 14, 2025 at 08:03:20AM -0700, Rob Clark wrote:
> > > On Sat, Jun 14, 2025 at 3:39 AM Danilo Krummrich <d...@redhat.com> wrote:
> > > >
> > > > On Fri, Jun 13, 2025 at 04:57:03PM -0700, Rob Clark wrote:
> > > > > For UNMAP/REMAP steps we could be needing to lock objects that are not
> > > > > explicitly listed in the VM_BIND ioctl in order to tear-down unmapped
> > > > > VAs. These helpers handle locking/preparing the needed objects.
> > > >
> > > > Yes, that's a common use-case. I think drivers typically iterate
> > > > through their
> > > > drm_gpuva_ops to lock those objects.
> > > >
> > > > I had a look at you link [1] and it seems that you keep a list of ops
> > > > as well by
> > > > calling vm_op_enqueue() with a new struct msm_vm_op from the callbacks.
> > > >
> > > > Please note that for exactly this case there is the op_alloc callback in
> > > > struct drm_gpuvm_ops, such that you can allocate a custom op type (i.e.
> > > > struct
> > > > msm_vm_op) that embedds a struct drm_gpuva_op.
> > >
> > > I did use drm_gpuvm_sm_xyz_ops_create() in an earlier iteration of my
> > > VM_BIND series, but it wasn't quite what I was after. I wanted to
> > > apply the VM updates immediately to avoid issues with a later
> > > map/unmap overlapping an earlier map, which
> > > drm_gpuvm_sm_xyz_ops_create() doesn't really handle. I'm not even
> > > sure why this isn't a problem for other drivers unless userspace is
> > > providing some guarantees.
> >
> > The drm_gpuva_ops are usually used in a pattern like this.
> >
> > vm_bind {
> > for_each_vm_bind_operation {
drm_gpuvm_sm_xyz_ops_create();
> > drm_gpuva_for_each_op {
> > // modify drm_gpuvm's interval tree
> > // pre-allocate memory
> > // lock and prepare objects
> > }
> > }
> >
> > drm_sched_entity_push_job();
> > }
> >
> > run_job {
> > for_each_vm_bind_operation {
> > drm_gpuva_for_each_op {
> > // modify page tables
> > }
> > }
> > }
> >
> > run_job {
> > for_each_vm_bind_operation {
> > drm_gpuva_for_each_op {
> > // free page table structures, if any
> > // free unused pre-allocated memory
> > }
> > }
> > }
> >
> > What did you do instead to get map/unmap overlapping? Even more interesting,
> > what are you doing now?
>
> From what I can tell, the drivers using drm_gpva_for_each_op()/etc are
> doing drm_gpuva_remove() while iterating the ops list..
> drm_gpuvm_sm_xyz_ops_create() itself does not modify the VM. So this
> can only really work if you perform one MAP or UNMAP at a time. Or at
> least if you process the VM modifying part of the ops list before
> proceeding to the next op.
(Added the drm_gpuvm_sm_xyz_ops_create() step above.)
I went through the code you posted [1] and conceptually you're implementing
exactly the pattern I described above, i.e. you do:
vm_bind {
for_each_vm_bind_operation {
drm_gpuvm_sm_xyz_exec_lock();
}
for_each_vm_bind_operation {
drm_gpuvm_sm_xyz() {
// modify drm_gpuvm's interval tree
// create custom ops
}
}
drm_sched_entity_push_job();
}
run_job {
for_each_vm_bind_operation {
for_each_custom_op() {
// do stuff
}
}
}
However, GPUVM intends to solve your use-case with the following, semantically
identical, approach.
vm_bind {
for_each_vm_bind_operation {
drm_gpuvm_sm_xyz_ops_create();
drm_gpuva_for_each_op {
// modify drm_gpuvm's interval tree
// lock and prepare objects (1)
}
}
drm_sched_entity_push_job();
}
run_job {
for_each_vm_bind_operation {
drm_gpuva_for_each_op() {
// do stuff
}
}
}
(Note that GPUVM already supports to extend the existing OP structures; you
should take advantage of that.)
Hence, the helper we really want is to lock and prepare the objects at (1). I.e.
a helper that takes a pointer to a struct drm_gpuva_op and locks / validates the
corresponding objects.
[1]
https://gitlab.freedesktop.org/robclark/msm/-/blob/sparse-newer/drivers/gpu/drm/msm/msm_gem_vma.c
