Re: [EXTERNAL] [PATCH drm-misc-next 5/5] drm/imagination: vm: make use of GPUVM's drm_exec helper

[Danilo Krummrich]

On 11/28/23 11:47, Donald Robson wrote:
> Hi Danilo,
>
> Apologies - I guess I should have submitted a patch to handle zero fences in your
> locking functions with the final patch series.
>
> On Sat, 2023-11-25 at 00:36 +0100, Danilo Krummrich wrote:
> > *** CAUTION: This email originates from a source not known to Imagination Technologies. Think before you click a link or open an attachment ***
> >
> > Make use of GPUVM's drm_exec helper functions preventing direct access
> > to GPUVM internal data structures, such as the external object list.
> >
> > This is especially important to ensure following the locking rules
> > around the GPUVM external object list.
> >
> > Fixes: ff5f643de0bf ("drm/imagination: Add GEM and VM related code")
> > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/imagination/pvr_vm.c | 16 +++++-----------
> >   1 file changed, 5 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/imagination/pvr_vm.c b/drivers/gpu/drm/imagination/pvr_vm.c
> > index e0d74d9a6190..3f7888f5cc53 100644
> > --- a/drivers/gpu/drm/imagination/pvr_vm.c
> > +++ b/drivers/gpu/drm/imagination/pvr_vm.c
> > @@ -337,27 +337,21 @@ static int
> >   pvr_vm_bind_op_lock_resvs(struct drm_exec *exec, struct pvr_vm_bind_op *bind_op)
> >   {
> >   	drm_exec_until_all_locked(exec) {
> > -		struct drm_gem_object *r_obj = &bind_op->vm_ctx->dummy_gem;
> >   		struct drm_gpuvm *gpuvm = &bind_op->vm_ctx->gpuvm_mgr;
> >   		struct pvr_gem_object *pvr_obj = bind_op->pvr_obj;
> > -		struct drm_gpuvm_bo *gpuvm_bo;
> >   
> >   		/* Acquire lock on the vm_context's reserve object. */
> > -		int err = drm_exec_lock_obj(exec, r_obj);
> > +		int err = drm_gpuvm_prepare_vm(gpuvm, exec, 0);
> >   
> >   		drm_exec_retry_on_contention(exec);
> >   		if (err)
> >   			return err;
> >   
> >   		/* Acquire lock on all BOs in the context. */
> > -		list_for_each_entry(gpuvm_bo, &gpuvm->extobj.list,
> > -				    list.entry.extobj) {
> > -			err = drm_exec_lock_obj(exec, gpuvm_bo->obj);
> > -
> > -			drm_exec_retry_on_contention(exec);
> > -			if (err)
> > -				return err;
> > -		}
> > +		err = drm_gpuvm_prepare_objects(gpuvm, exec, 0);
> > +		drm_exec_retry_on_contention(exec);
> > +		if (err)
> > +			return err;
>
> Before I discovered the problem when not reserving fences, I was trying to use
> drm_gpuvm_exec_lock() with vm_exec->extra.fn() for the part below.  Is there
> a reason not to do that now?

No, that works - gonna change that.

- Danilo

> Many thanks,
> Donald
>
> >   
> >   		/* Unmap operations don't have an object to lock. */
> >   		if (!pvr_obj)