Re: [PATCH v3 7/8] drm/nouveau: use DRM_GPUVM_RESV_PROTECTED

[Matthew Brost <matthew.brost@intel.com>]

On Sat, Oct 17, 2026 at 06:02:26PM -0700, Matthew Brost wrote:
> On Sat, Oct 17, 2026 at 11:31:06PM +0200, Danilo Krummrich wrote:
> > On Fri Oct 2, 2026 at 12:06 AM CEST, Matthew Brost wrote:
> > > @@ -1187,6 +1187,27 @@ bind_validate_region(struct nouveau_job *job)
> > >  	return 0;
> > >  }
> > >  
> > > +/*
> > > + * Lock the VM's common dma-resv together with the one of @obj, as needed to
> > > + * drop what may be the last reference of a &drm_gpuvm_bo.
> > > + */
> > > +static void
> > > +nouveau_uvmm_lock_vm_and_obj(struct nouveau_uvmm *uvmm, struct drm_exec *exec,
> > > +			     struct drm_gem_object *obj)
> > > +{
> > > +	int ret;
> > > +
> > > +	drm_exec_init(exec, DRM_EXEC_IGNORE_DUPLICATES, 2);
> > > +	drm_exec_until_all_locked(exec) {
> > > +		ret = drm_exec_lock_obj(exec, drm_gpuvm_resv_obj(&uvmm->base));
> > > +		if (!ret)
> > > +			ret = drm_exec_lock_obj(exec, obj);
> > 
> > What happens if we reach this with ENOMEM? In such a case we may return without
> 
> Right, valid issue. Sashiko flagged this too.
> 
> Originally, I thought we would need to open-code the WW transaction, but
> instead I ended up fixing drm_exec [1].
> 
> So I think we should merge [1] and run the MSM and Nouveau work in a
> no-failure mode.
> 
> One thing I'd add is an assert(!ret) if Nouveau has support for that
> (see xe_assert.h for what we do in Xe so our CI can catch things we
> believe are impossible). I suppose the open-coded version would be a
> WARN_ON() or WARN_ON_ONCE().
> 
> Also likey a BUILD_BUG_ON(2 <= DRM_EXEC_INLINE_OBJECTS).
> 

Ugh, logic inversion.

Rather:

BUILD_BUG_ON(2 > DRM_EXEC_INLINE_OBJECTS)

Matt

> Let me know if you want me to respin with these changes.
> 
> Matt 
> 
> [1] https://patchwork.freedesktop.org/series/175390/
> 
> > any locks being held and nouveau would just continue calling into function that
> > expect locks to be held and hence produced UB, right?
> > 
> > (I think there is a similar case in MSM, but it was pre-existing, so I picked all
> > other patches.)
> > 
> > > +		drm_exec_retry_on_contention(exec);
> > > +		if (drm_WARN_ON(uvmm->base.drm, ret))
> > > +			break;
> > > +	}
> > > +}