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Date:   Wed, 13 Sep 2023 01:36:52 +0200
From:   Danilo Krummrich <dakr@redhat.com>
To:     Thomas =?iso-8859-1?Q?Hellstr=F6m?= 
        <thomas.hellstrom@linux.intel.com>
Cc:     airlied@gmail.com, daniel@ffwll.ch, matthew.brost@intel.com,
        sarah.walker@imgtec.com, donald.robson@imgtec.com,
        boris.brezillon@collabora.com, christian.koenig@amd.com,
        faith.ekstrand@collabora.com, dri-devel@lists.freedesktop.org,
        nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH drm-misc-next v3 6/7] drm/gpuvm: generalize
 dma_resv/extobj handling and GEM validation
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References: <20230909153125.30032-1-dakr@redhat.com>
 <20230909153125.30032-7-dakr@redhat.com>
 <a9ef04d2-2525-65c0-2eda-45ca9a95a3a0@linux.intel.com>
 <ZQCW6wzHYVdxl/IV@pollux>
 <701dfead-e240-b3fb-422c-d49fc7e04595@linux.intel.com>
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On Tue, Sep 12, 2023 at 09:23:08PM +0200, Thomas Hellstr?m wrote:
> 
> On 9/12/23 18:50, Danilo Krummrich wrote:
> > On Tue, Sep 12, 2023 at 06:20:32PM +0200, Thomas Hellstr?m wrote:
> > > Hi, Danilo,
> > > 
> > > On 9/9/23 17:31, Danilo Krummrich wrote:
> > > > So far the DRM GPUVA manager offers common infrastructure to track GPU VA
> > > > allocations and mappings, generically connect GPU VA mappings to their
> > > > backing buffers and perform more complex mapping operations on the GPU VA
> > > > space.
> > > > 
> > > > However, there are more design patterns commonly used by drivers, which
> > > > can potentially be generalized in order to make the DRM GPUVA manager
> > > > represent a basic GPU-VM implementation. In this context, this patch aims
> > > > at generalizing the following elements.
> > > > 
> > > > 1) Provide a common dma-resv for GEM objects not being used outside of
> > > >      this GPU-VM.
> > > > 
> > > > 2) Provide tracking of external GEM objects (GEM objects which are
> > > >      shared with other GPU-VMs).
> > > > 
> > > > 3) Provide functions to efficiently lock all GEM objects dma-resv the
> > > >      GPU-VM contains mappings of.
> > > > 
> > > > 4) Provide tracking of evicted GEM objects the GPU-VM contains mappings
> > > >      of, such that validation of evicted GEM objects is accelerated.
> > > > 
> > > > 5) Provide some convinience functions for common patterns.
> > > > 
> > > > Rather than being designed as a "framework", the target is to make all
> > > > features appear as a collection of optional helper functions, such that
> > > > drivers are free to make use of the DRM GPUVA managers basic
> > > > functionality and opt-in for other features without setting any feature
> > > > flags, just by making use of the corresponding functions.
> > > > 
> > > > Big kudos to Boris Brezillon for his help to figure out locking for drivers
> > > > updating the GPU VA space within the fence signalling path.
> > > > 
> > > > Suggested-by: Matthew Brost <matthew.brost@intel.com>
> > > > Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> > > > ---
> > > >    drivers/gpu/drm/drm_gpuvm.c | 516 ++++++++++++++++++++++++++++++++++++
> > > >    include/drm/drm_gpuvm.h     | 197 ++++++++++++++
> > > >    2 files changed, 713 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
> > > > index f4411047dbb3..8e62a043f719 100644
> > > > --- a/drivers/gpu/drm/drm_gpuvm.c
> > > > +++ b/drivers/gpu/drm/drm_gpuvm.c
> > > > @@ -73,6 +73,21 @@
> > > >     * &drm_gem_object list of &drm_gpuvm_bos for an existing instance of this
> > > >     * particular combination. If not existent a new instance is created and linked
> > > >     * to the &drm_gem_object.
> > > > + *
> > > > + * &drm_gpuvm_bo structures, since unique for a given &drm_gpuvm, are also used
> > > > + * as entry for the &drm_gpuvm's lists of external and evicted objects. Those
> > > > + * list are maintained in order to accelerate locking of dma-resv locks and
> > > > + * validation of evicted objects bound in a &drm_gpuvm. For instance the all
> > > > + * &drm_gem_object's &dma_resv of a given &drm_gpuvm can be locked by calling
> > > > + * drm_gpuvm_exec_lock(). Once locked drivers can call drm_gpuvm_validate() in
> > > > + * order to validate all evicted &drm_gem_objects. It is also possible to lock
> > > > + * additional &drm_gem_objects by providing the corresponding parameters to
> > > > + * drm_gpuvm_exec_lock() as well as open code the &drm_exec loop while making
> > > > + * use of helper functions such as drm_gpuvm_prepare_range() or
> > > > + * drm_gpuvm_prepare_objects().
> > > > + *
> > > > + * Every bound &drm_gem_object is treated as external object when its &dma_resv
> > > > + * structure is different than the &drm_gpuvm's common &dma_resv structure.
> > > >     */
> > > >    /**
> > > > @@ -420,6 +435,20 @@
> > > >     * Subsequent calls to drm_gpuvm_bo_obtain() for the same &drm_gpuvm and
> > > >     * &drm_gem_object must be able to observe previous creations and destructions
> > > >     * of &drm_gpuvm_bos in order to keep instances unique.
> > > > + *
> > > > + * The &drm_gpuvm's lists for keeping track of external and evicted objects are
> > > > + * protected against concurrent insertion / removal and iteration internally.
> > > > + *
> > > > + * However, drivers still need ensure to protect concurrent calls to functions
> > > > + * iterating those lists, such as drm_gpuvm_validate() and
> > > > + * drm_gpuvm_prepare_objects(). Every such function contains a particular
> > > > + * comment and lockdep checks if possible.
> > > > + *
> > > > + * Functions adding or removing entries from those lists, such as
> > > > + * drm_gpuvm_bo_evict() or drm_gpuvm_bo_extobj_add() may be called with external
> > > > + * locks being held, e.g. in order to avoid the corresponding list to be
> > > > + * (safely) modified while potentially being iternated by other API functions.
> > > > + * However, this is entirely optional.
> > > >     */
> > > >    /**
> > > > @@ -632,6 +661,131 @@
> > > >     *	}
> > > >     */
> > > > +/**
> > > > + * get_next_vm_bo_from_list() - get the next vm_bo element
> > > > + * @__gpuvm: The GPU VM
> > > > + * @__list_name: The name of the list we're iterating on
> > > > + * @__local_list: A pointer to the local list used to store already iterated items
> > > > + * @__prev_vm_bo: The previous element we got from drm_gpuvm_get_next_cached_vm_bo()
> > > > + *
> > > > + * This helper is here to provide lockless list iteration. Lockless as in, the
> > > > + * iterator releases the lock immediately after picking the first element from
> > > > + * the list, so list insertion deletion can happen concurrently.
> > > Are the list spinlocks needed for that async state update from within the
> > > dma-fence critical section we've discussed previously?
> > Yes, but also for other reasons, see below.
> > 
> > > Otherwise it should be sufficient to protect the lists with the gpuvm's resv
> > > (or for the extobj list with an outer lock).
> > > 
> > > If those spinlocks are still needed in some situations, perhaps could we
> > > have an option to set them to NULL (Like IIRC the maple tree allows for)?
> > The evict spinlock is needed in any case, since in drm_gpuvm_bo_evict() we're
> > holding only the dma-resv lock from the BO this function gets called for. Hence,
> > the spinlock protects concurrent drm_gpuvm_bo_evict() calls with different BOs.
> No. Only if you try to add external objects to the vm's evict list from
> within the evict code. That's not necessary since you loop through all
> external objects anyway when locking them so an "evicted" bool in the vm_bo,
> protected by the bo resv would be sufficient. The extobj locking loop can
> then add the bo to the evicted list.

And validate() can remove it while still holding all dma-resv locks, neat!
However, what if two tasks are trying to lock the VA space concurrently? What
do we do when the drm_gpuvm_bo's refcount drops to zero in drm_gpuva_unlink()?
Are we guaranteed that at this point of time the drm_gpuvm_bo is not on the
evicted list? Because otherwise we would call drm_gpuvm_bo_destroy() with the
dma-resv lock held, which wouldn't be allowed, since drm_gpuvm_bo_destroy()
might drop the last reference to the drm_gem_object and hence we'd potentially
free the dma-resv lock while holding it, at least if it's an external object.

> > 
> > For extobjs an outer lock would be enough in case of Xe, but I really would not
> > like to add even more complexity just to get the spinlock out of the way in case
> > the driver already has an outer lock protecting this path.
> 
> I must disagree here. These spinlocks and atomic operations are pretty
> costly and as discussed earlier this type of locking was the reason (at
> least according to the commit message) that made Christian drop the XArray
> use in drm_exec for the same set of objects: "The locking overhead is
> unecessary and measurable". IMHO the spinlock is the added complexity and a
> single wide lock following the drm locking guidelines set out by Daniel and
> David should really be the default choice with an opt-in for a spinlock if
> needed for async and pushing out to a wq is not an option.

For the external object list an outer lock would work as long as it's not the
dma-resv lock of the corresponding GEM object, since here we actually need to
remove the list entry from the external object list on drm_gpuvm_bo_destroy().
It's just a bit weird design wise that drivers would need to take this outer
lock on:

- drm_gpuvm_bo_extobj_add()
- drm_gpuvm_bo_destroy()	(and hence also drm_gpuvm_bo_put())
- drm_gpuva_unlink() 		(because it needs to call drm_gpuvm_bo_put())
- drm_gpuvm_exec_lock()
- drm_gpuvm_exec_lock_array()
- drm_gpuvm_prepare_range()

Given that it seems reasonable to do all the required locking internally.

In order to at least place lockdep checks, the driver would need to supply the
corresponding lock's lockdep_map, because the GPUVM otherwise doesn't know about
the lock.

Out of curiosity, what is the overhead of a spin_lock() that doesn't need to
spin? 

> 
> A pretty simple way that would not add much code would be
> 
> static void gpuvm_cond_spin_lock(const struct drm_gpuvm *gpuvm, spinlock_t
> *lock)
> 
> {
> 
> ??? if (!gpuvm->resv_protected_lists)
> ??? ??? spin_lock(lock);
> 
> }
> 
> > > For such drivers, that would require anybody calling unlink to hold the vm's
> > > resv, though.
> > In V4 I want to go back to having a dedicated lock for the GEMs gpuva list (or
> > VM_BO list to be more precise). We can't just use the dma-resv lock for that
> > with VM_BO abstractions, because on destruction of a VM_BO we otherwise wouldn't
> > be allowed to already hold the dma-resv lock. That's the fix I was referring to
> > earlier.
> 
> Yeah, I can see the need for a dedicated lock for the GEM's gpuva list, but
> holding the vm's dma-resv lock across the unlink shouldn't be a problem. We
> may free the object and a pointer to the vm's resv during unlink but we
> don't free the vm's resv.? It'd be a matter of ensuring that any calls to
> unlink from *within* drm_gpuvm allows it to be held.

Drivers calling unlink() from the fence signaling path can't use the VM's
dma-resv lock.

Also, what if the object is an external object? We can't use the VM's dma-resv
lock here. And we can't have the GEM objs dma-resv lock held when calling
unlink(), since unlink() calls drm_gpuvm_bo_put(), which if the refcount drops
to zero calls drm_gpuvm_bo_destroy() and drm_gpuvm_bo_destroy() might drop the
last reference of the GEM object. All those problems go away with a dedicated
GEM gpuva list lock.

> 
> /Thomas
> 
> 
> > > It seems that with that also the refcount could be make non-atomic.
> > > 
> > > All in the spirit of the drm locking guidelines "use big locks when
> > > possible".
> > > Lower level locks only when necessary for performance or locking inversion?
> > > 
> > > /Thomas
> > > 
> > > 
> > > > + *
> > > > + * Elements popped from the original list are kept in a local list, so removal
> > > > + * and is_empty checks can still happen while we're iterating the list.
> > > > + */
> > > > +#define get_next_vm_bo_from_list(__gpuvm, __list_name, __local_list, __prev_vm_bo)	\
> > > > +	({										\
> > > > +		struct drm_gpuvm_bo *__vm_bo;						\
> > > > +											\
> > > > +		drm_gpuvm_bo_put(__prev_vm_bo);						\
> > > > +											\
> > > > +		spin_lock(&(__gpuvm)->__list_name.lock);				\
> > > > +		while (!list_empty(&(__gpuvm)->__list_name.list)) {			\
> > > > +			__vm_bo = list_first_entry(&(__gpuvm)->__list_name.list,	\
> > > > +						   struct drm_gpuvm_bo,			\
> > > > +						   list.entry.__list_name);		\
> > > > +			if (drm_gpuvm_bo_get_unless_zero(__vm_bo)) {			\
> > > > +				list_move_tail(&(__vm_bo)->list.entry.__list_name,	\
> > > > +					       __local_list);				\
> > > > +				break;							\
> > > > +			} else {							\
> > > > +				list_del_init(&(__vm_bo)->list.entry.__list_name);	\
> > > > +				__vm_bo = NULL;						\
> > > > +			}								\
> > > > +		}									\
> > > > +		spin_unlock(&(__gpuvm)->__list_name.lock);				\
> > > > +											\
> > > > +		__vm_bo;								\
> > > > +	})
> > > > +
> > > > +/**
> > > > + * for_each_vm_bo_in_list() - internal vm_bo list iterator
> > > > + *
> > > > + * This helper is here to provide lockless list iteration. Lockless as in, the
> > > > + * iterator releases the lock immediately after picking the first element from the
> > > > + * list, so list insertion and deletion can happen concurrently.
> > > > + *
> > > > + * Typical use:
> > > > + *
> > > > + *	struct drm_gpuvm_bo *vm_bo;
> > > > + *	LIST_HEAD(my_local_list);
> > > > + *
> > > > + *	ret = 0;
> > > > + *	drm_gpuvm_for_each_vm_bo(gpuvm, <list_name>, &my_local_list, vm_bo) {
> > > > + *		ret = do_something_with_vm_bo(..., vm_bo);
> > > > + *		if (ret)
> > > > + *			break;
> > > > + *	}
> > > > + *	drm_gpuvm_bo_put(vm_bo);
> > > > + *	drm_gpuvm_restore_vm_bo_list(gpuvm, <list_name>, &my_local_list);
> > > > + *
> > > > + *
> > > > + * Only used for internal list iterations, not meant to be exposed to the outside
> > > > + * world.
> > > > + */
> > > > +#define for_each_vm_bo_in_list(__gpuvm, __list_name, __local_list, __vm_bo)	\
> > > > +	for (__vm_bo = get_next_vm_bo_from_list(__gpuvm, __list_name,		\
> > > > +						__local_list, NULL);		\
> > > > +	     __vm_bo;								\
> > > > +	     __vm_bo = get_next_vm_bo_from_list(__gpuvm, __list_name,		\
> > > > +						__local_list, __vm_bo))		\
> > > > +
> > > > +/**
> > > > + * restore_vm_bo_list() - move vm_bo elements back to their original list
> > > > + * @__gpuvm: The GPU VM
> > > > + * @__list_name: The name of the list we're iterating on
> > > > + * @__local_list: A pointer to the local list used to store already iterated items
> > > > + *
> > > > + * When we're done iterating a vm_bo list, we should call restore_vm_bo_list()
> > > > + * to restore the original state and let new iterations take place.
> > > > + */
> > > > +#define restore_vm_bo_list(__gpuvm, __list_name, __local_list)				\
> > > > +	do {										\
> > > > +		/* Merge back the two lists, moving local list elements to the		\
> > > > +		 * head to preserve previous ordering, in case it matters.		\
> > > > +		 */									\
> > > > +		spin_lock(&(__gpuvm)->__list_name.lock);				\
> > > > +		list_splice(__local_list, &(__gpuvm)->__list_name.list);		\
> > > > +		spin_unlock(&(__gpuvm)->__list_name.lock);				\
> > > > +	} while (0)
> > > > +/**
> > > > + * drm_gpuvm_bo_list_add() - insert a vm_bo into the given list
> > > > + * @__vm_bo: the &drm_gpuvm_bo
> > > > + * @__list_name: the name of the list to insert into
> > > > + *
> > > > + * Inserts the given @__vm_bo into the list specified by @__list_name and
> > > > + * increases the vm_bo's reference count.
> > > > + */
> > > > +#define drm_gpuvm_bo_list_add(__vm_bo, __list_name)				\
> > > > +	do {									\
> > > > +		spin_lock(&(__vm_bo)->vm->__list_name.lock);			\
> > > > +		if (list_empty(&(__vm_bo)->list.entry.__list_name))		\
> > > > +			list_add_tail(&(__vm_bo)->list.entry.__list_name,	\
> > > > +				      &(__vm_bo)->vm->__list_name.list);	\
> > > > +		spin_unlock(&(__vm_bo)->vm->__list_name.lock);			\
> > > > +	} while (0)
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_bo_list_del() - remove a vm_bo from the given list
> > > > + * @__vm_bo: the &drm_gpuvm_bo
> > > > + * @__list_name: the name of the list to insert into
> > > > + *
> > > > + * Removes the given @__vm_bo from the list specified by @__list_name and
> > > > + * decreases the vm_bo's reference count.
> > > > + */
> > > > +#define drm_gpuvm_bo_list_del(__vm_bo, __list_name)				\
> > > > +	do {									\
> > > > +		spin_lock(&(__vm_bo)->vm->__list_name.lock);			\
> > > > +		if (!list_empty(&(__vm_bo)->list.entry.__list_name))		\
> > > > +			list_del_init(&(__vm_bo)->list.entry.__list_name);	\
> > > > +		spin_unlock(&(__vm_bo)->vm->__list_name.lock);			\
> > > > +	} while (0)
> > > > +
> > > > +static int __must_check
> > > > +drm_gpuvm_bo_get_unless_zero(struct drm_gpuvm_bo *vm_bo);
> > > > +
> > > >    #define to_drm_gpuva(__node)	container_of((__node), struct drm_gpuva, rb.node)
> > > >    #define GPUVA_START(node) ((node)->va.addr)
> > > > @@ -713,6 +867,12 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_device *drm,
> > > >    	gpuvm->rb.tree = RB_ROOT_CACHED;
> > > >    	INIT_LIST_HEAD(&gpuvm->rb.list);
> > > > +	INIT_LIST_HEAD(&gpuvm->extobj.list);
> > > > +	spin_lock_init(&gpuvm->extobj.lock);
> > > > +
> > > > +	INIT_LIST_HEAD(&gpuvm->evict.list);
> > > > +	spin_lock_init(&gpuvm->evict.lock);
> > > > +
> > > >    	drm_gpuva_check_overflow(start_offset, range);
> > > >    	gpuvm->mm_start = start_offset;
> > > >    	gpuvm->mm_range = range;
> > > > @@ -754,10 +914,302 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
> > > >    	WARN(!RB_EMPTY_ROOT(&gpuvm->rb.tree.rb_root),
> > > >    	     "GPUVA tree is not empty, potentially leaking memory.\n");
> > > > +	WARN(!list_empty(&gpuvm->extobj.list), "Extobj list should be empty.\n");
> > > > +	WARN(!list_empty(&gpuvm->evict.list), "Evict list should be empty.\n");
> > > > +
> > > >    	drm_gem_private_object_fini(&gpuvm->d_obj);
> > > >    }
> > > >    EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
> > > > +/**
> > > > + * drm_gpuvm_prepare_objects() - prepare all assoiciated BOs
> > > > + * @gpuvm: the &drm_gpuvm
> > > > + * @exec: the &drm_exec locking context
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + *
> > > > + * Calls drm_exec_prepare_obj() for all &drm_gem_objects the given
> > > > + * &drm_gpuvm contains mappings of.
> > > > + *
> > > > + * Using this function directly, it is the drivers responsibility to call
> > > > + * drm_exec_init() and drm_exec_fini() accordingly.
> > > > + *
> > > > + * Note: This function is safe against concurrent insertion and removal of
> > > > + * external objects, however it is not safe against concurrent usage itself.
> > > > + *
> > > > + * Drivers need to make sure to protect this case with either an outer VM lock
> > > > + * or by calling drm_gpuvm_prepare_vm() before this function within the
> > > > + * drm_exec_until_all_locked() loop, such that the GPUVM's dma-resv lock ensures
> > > > + * mutual exclusion.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
> > > > +			  struct drm_exec *exec,
> > > > +			  unsigned int num_fences)
> > > > +{
> > > > +	struct drm_gpuvm_bo *vm_bo;
> > > > +	LIST_HEAD(extobjs);
> > > > +	int ret = 0;
> > > > +
> > > > +	for_each_vm_bo_in_list(gpuvm, extobj, &extobjs, vm_bo) {
> > > > +		ret = drm_exec_prepare_obj(exec, vm_bo->obj, num_fences);
> > > > +		if (ret)
> > > > +			break;
> > > > +	}
> > > > +	/* Drop ref in case we break out of the loop. */
> > > > +	drm_gpuvm_bo_put(vm_bo);
> > > > +	restore_vm_bo_list(gpuvm, extobj, &extobjs);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_prepare_objects);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_prepare_range() - prepare all BOs mapped within a given range
> > > > + * @gpuvm: the &drm_gpuvm
> > > > + * @exec: the &drm_exec locking context
> > > > + * @addr: the start address within the VA space
> > > > + * @range: the range to iterate within the VA space
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + *
> > > > + * Calls drm_exec_prepare_obj() for all &drm_gem_objects mapped between @addr
> > > > + * and @addr + @range.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_prepare_range(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
> > > > +			u64 addr, u64 range, unsigned int num_fences)
> > > > +{
> > > > +	struct drm_gpuva *va;
> > > > +	u64 end = addr + range;
> > > > +	int ret;
> > > > +
> > > > +	drm_gpuvm_for_each_va_range(va, gpuvm, addr, end) {
> > > > +		struct drm_gem_object *obj = va->gem.obj;
> > > > +
> > > > +		ret = drm_exec_prepare_obj(exec, obj, num_fences);
> > > > +		if (ret)
> > > > +			return ret;
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_prepare_range);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_exec_lock() - lock all dma-resv of all assoiciated BOs
> > > > + * @vm_exec: the &drm_gpuvm_exec abstraction
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + * @interruptible: sleep interruptible if waiting
> > > > + *
> > > > + * Acquires all dma-resv locks of all &drm_gem_objects the given
> > > > + * &drm_gpuvm contains mappings of.
> > > > + *
> > > > + * Addionally, when calling this function with struct drm_gpuvm_exec::extra
> > > > + * being set the driver receives the given @fn callback to lock additional
> > > > + * dma-resv in the context of the &drm_gpuvm_exec instance. Typically, drivers
> > > > + * would call drm_exec_prepare_obj() from within this callback.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_exec_lock(struct drm_gpuvm_exec *vm_exec,
> > > > +		    unsigned int num_fences,
> > > > +		    bool interruptible)
> > > > +{
> > > > +	struct drm_gpuvm *gpuvm = vm_exec->vm;
> > > > +	struct drm_exec *exec = &vm_exec->exec;
> > > > +	uint32_t flags;
> > > > +	int ret;
> > > > +
> > > > +	flags = interruptible ? DRM_EXEC_INTERRUPTIBLE_WAIT : 0 |
> > > > +		DRM_EXEC_IGNORE_DUPLICATES;
> > > > +
> > > > +	drm_exec_init(exec, flags);
> > > > +
> > > > +	drm_exec_until_all_locked(exec) {
> > > > +		ret = drm_gpuvm_prepare_vm(gpuvm, exec, num_fences);
> > > > +		drm_exec_retry_on_contention(exec);
> > > > +		if (ret)
> > > > +			goto err;
> > > > +
> > > > +		ret = drm_gpuvm_prepare_objects(gpuvm, exec, num_fences);
> > > > +		drm_exec_retry_on_contention(exec);
> > > > +		if (ret)
> > > > +			goto err;
> > > > +
> > > > +		if (vm_exec->extra.fn) {
> > > > +			ret = vm_exec->extra.fn(vm_exec, num_fences);
> > > > +			drm_exec_retry_on_contention(exec);
> > > > +			if (ret)
> > > > +				goto err;
> > > > +		}
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +
> > > > +err:
> > > > +	drm_exec_fini(exec);
> > > > +	return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock);
> > > > +
> > > > +static int
> > > > +fn_lock_array(struct drm_gpuvm_exec *vm_exec, unsigned int num_fences)
> > > > +{
> > > > +	struct {
> > > > +		struct drm_gem_object **objs;
> > > > +		unsigned int num_objs;
> > > > +	} *args = vm_exec->extra.priv;
> > > > +
> > > > +	return drm_exec_prepare_array(&vm_exec->exec, args->objs,
> > > > +				      args->num_objs, num_fences);
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_exec_lock_array() - lock all dma-resv of all assoiciated BOs
> > > > + * @vm_exec: the &drm_gpuvm_exec abstraction
> > > > + * @objs: additional &drm_gem_objects to lock
> > > > + * @num_objs: the number of additional &drm_gem_objects to lock
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + * @interruptible: sleep interruptible if waiting
> > > > + *
> > > > + * Acquires all dma-resv locks of all &drm_gem_objects the given &drm_gpuvm
> > > > + * contains mappings of, plus the ones given through @objs.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_exec_lock_array(struct drm_gpuvm_exec *vm_exec,
> > > > +			  struct drm_gem_object **objs,
> > > > +			  unsigned int num_objs,
> > > > +			  unsigned int num_fences,
> > > > +			  bool interruptible)
> > > > +{
> > > > +	struct {
> > > > +		struct drm_gem_object **objs;
> > > > +		unsigned int num_objs;
> > > > +	} args;
> > > > +
> > > > +	args.objs = objs;
> > > > +	args.num_objs = num_objs;
> > > > +
> > > > +	vm_exec->extra.fn = fn_lock_array;
> > > > +	vm_exec->extra.priv = &args;
> > > > +
> > > > +	return drm_gpuvm_exec_lock(vm_exec, num_fences, interruptible);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock_array);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_exec_lock_range() - prepare all BOs mapped within a given range
> > > > + * @vm_exec: the &drm_gpuvm_exec abstraction
> > > > + * @addr: the start address within the VA space
> > > > + * @range: the range to iterate within the VA space
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + * @interruptible: sleep interruptible if waiting
> > > > + *
> > > > + * Acquires all dma-resv locks of all &drm_gem_objects mapped between @addr and
> > > > + * @addr + @range.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_exec_lock_range(struct drm_gpuvm_exec *vm_exec,
> > > > +			  u64 addr, u64 range,
> > > > +			  unsigned int num_fences,
> > > > +			  bool interruptible)
> > > > +{
> > > > +	struct drm_gpuvm *gpuvm = vm_exec->vm;
> > > > +	struct drm_exec *exec = &vm_exec->exec;
> > > > +	uint32_t flags;
> > > > +	int ret;
> > > > +
> > > > +	flags = interruptible ? DRM_EXEC_INTERRUPTIBLE_WAIT : 0 |
> > > > +		DRM_EXEC_IGNORE_DUPLICATES;
> > > > +
> > > > +	drm_exec_init(exec, flags);
> > > > +
> > > > +	drm_exec_until_all_locked(exec) {
> > > > +		ret = drm_gpuvm_prepare_range(gpuvm, exec, addr, range,
> > > > +					      num_fences);
> > > > +		drm_exec_retry_on_contention(exec);
> > > > +		if (ret)
> > > > +			goto err;
> > > > +	}
> > > > +
> > > > +	return ret;
> > > > +
> > > > +err:
> > > > +	drm_exec_fini(exec);
> > > > +	return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock_range);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_validate() - validate all BOs marked as evicted
> > > > + * @gpuvm: the &drm_gpuvm to validate evicted BOs
> > > > + *
> > > > + * Calls the &drm_gpuvm_ops.bo_validate callback for all evicted buffer
> > > > + * objects being mapped in the given &drm_gpuvm.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuvm_validate(struct drm_gpuvm *gpuvm)
> > > > +{
> > > > +	const struct drm_gpuvm_ops *ops = gpuvm->ops;
> > > > +	struct drm_gpuvm_bo *vm_bo;
> > > > +	LIST_HEAD(evict);
> > > > +	int ret = 0;
> > > > +
> > > > +	if (unlikely(!ops || !ops->bo_validate))
> > > > +		return -ENOTSUPP;
> > > > +
> > > > +	for_each_vm_bo_in_list(gpuvm, evict, &evict, vm_bo) {
> > > > +		dma_resv_assert_held(vm_bo->obj->resv);
> > > > +		ret = ops->bo_validate(vm_bo->obj);
> > > > +		if (ret)
> > > > +			break;
> > > > +	}
> > > > +	/* Drop ref in case we break out of the loop. */
> > > > +	drm_gpuvm_bo_put(vm_bo);
> > > > +	restore_vm_bo_list(gpuvm, evict, &evict);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_validate);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_resv_add_fence - add fence to private and all extobj
> > > > + * dma-resv
> > > > + * @gpuvm: the &drm_gpuvm to add a fence to
> > > > + * @exec: the &drm_exec locking context
> > > > + * @fence: fence to add
> > > > + * @private_usage: private dma-resv usage
> > > > + * @extobj_usage: extobj dma-resv usage
> > > > + */
> > > > +void
> > > > +drm_gpuvm_resv_add_fence(struct drm_gpuvm *gpuvm,
> > > > +			 struct drm_exec *exec,
> > > > +			 struct dma_fence *fence,
> > > > +			 enum dma_resv_usage private_usage,
> > > > +			 enum dma_resv_usage extobj_usage)
> > > > +{
> > > > +	struct drm_gem_object *obj;
> > > > +	unsigned long index;
> > > > +
> > > > +	drm_exec_for_each_locked_object(exec, index, obj) {
> > > > +		dma_resv_assert_held(obj->resv);
> > > > +		dma_resv_add_fence(obj->resv, fence,
> > > > +				   drm_gpuvm_is_extobj(gpuvm, obj) ?
> > > > +				   private_usage : extobj_usage);
> > > > +	}
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_resv_add_fence);
> > > > +
> > > >    /**
> > > >     * drm_gpuvm_bo_create() - create a new instance of struct drm_gpuvm_bo
> > > >     * @gpuvm: The &drm_gpuvm the @obj is mapped in.
> > > > @@ -790,6 +1242,9 @@ drm_gpuvm_bo_create(struct drm_gpuvm *gpuvm,
> > > >    	INIT_LIST_HEAD(&vm_bo->list.gpuva);
> > > >    	INIT_LIST_HEAD(&vm_bo->list.entry.gem);
> > > > +	INIT_LIST_HEAD(&vm_bo->list.entry.extobj);
> > > > +	INIT_LIST_HEAD(&vm_bo->list.entry.evict);
> > > > +
> > > >    	drm_gem_object_get(obj);
> > > >    	return vm_bo;
> > > > @@ -807,6 +1262,14 @@ drm_gpuvm_bo_destroy(struct kref *kref)
> > > >    	drm_gem_gpuva_assert_lock_held(vm_bo->obj);
> > > > +	spin_lock(&gpuvm->extobj.lock);
> > > > +	list_del(&vm_bo->list.entry.extobj);
> > > > +	spin_unlock(&gpuvm->extobj.lock);
> > > > +
> > > > +	spin_lock(&gpuvm->evict.lock);
> > > > +	list_del(&vm_bo->list.entry.evict);
> > > > +	spin_unlock(&gpuvm->evict.lock);
> > > > +
> > > >    	list_del(&vm_bo->list.entry.gem);
> > > >    	drm_gem_object_put(obj);
> > > > @@ -822,6 +1285,11 @@ drm_gpuvm_bo_destroy(struct kref *kref)
> > > >     * @vm_bo: the &drm_gpuvm_bo to release the reference of
> > > >     *
> > > >     * This releases a reference to @vm_bo.
> > > > + *
> > > > + * If the reference count drops to zero, the &gpuvm_bo is destroyed, which
> > > > + * includes removing it from the GEMs gpuva list. Hence, if a call to this
> > > > + * function can potentially let the reference count to zero the caller must
> > > > + * hold the dma-resv or driver specific GEM gpuva lock.
> > > >     */
> > > >    void
> > > >    drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo)
> > > > @@ -831,6 +1299,12 @@ drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo)
> > > >    }
> > > >    EXPORT_SYMBOL_GPL(drm_gpuvm_bo_put);
> > > > +static int __must_check
> > > > +drm_gpuvm_bo_get_unless_zero(struct drm_gpuvm_bo *vm_bo)
> > > > +{
> > > > +	return kref_get_unless_zero(&vm_bo->kref);
> > > > +}
> > > > +
> > > >    static struct drm_gpuvm_bo *
> > > >    __drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> > > >    		    struct drm_gem_object *obj)
> > > > @@ -938,6 +1412,48 @@ drm_gpuvm_bo_obtain_prealloc(struct drm_gpuvm_bo *__vm_bo)
> > > >    }
> > > >    EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain_prealloc);
> > > > +/**
> > > > + * drm_gpuvm_bo_extobj_add() - adds the &drm_gpuvm_bo to its &drm_gpuvm's
> > > > + * extobj list
> > > > + * @vm_bo: The &drm_gpuvm_bo to add to its &drm_gpuvm's the extobj list.
> > > > + *
> > > > + * Adds the given @vm_bo to its &drm_gpuvm's extobj list if not on the list
> > > > + * already and if the corresponding &drm_gem_object is an external object,
> > > > + * actually.
> > > > + */
> > > > +void
> > > > +drm_gpuvm_bo_extobj_add(struct drm_gpuvm_bo *vm_bo)
> > > > +{
> > > > +	struct drm_gpuvm *gpuvm = vm_bo->vm;
> > > > +
> > > > +	if (drm_gpuvm_is_extobj(gpuvm, vm_bo->obj))
> > > > +		drm_gpuvm_bo_list_add(vm_bo, extobj);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_extobj_add);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_bo_evict() - add / remove a &drm_gem_object to / from a
> > > > + * &drm_gpuvms evicted list
> > > > + * @obj: the &drm_gem_object to add or remove
> > > > + * @evict: indicates whether the object is evicted
> > > > + *
> > > > + * Adds a &drm_gem_object to or removes it from all &drm_gpuvms evicted
> > > > + * list containing a mapping of this &drm_gem_object.
> > > > + */
> > > > +void
> > > > +drm_gpuvm_bo_evict(struct drm_gem_object *obj, bool evict)
> > > > +{
> > > > +	struct drm_gpuvm_bo *vm_bo;
> > > > +
> > > > +	drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
> > > > +		if (evict)
> > > > +			drm_gpuvm_bo_list_add(vm_bo, evict);
> > > > +		else
> > > > +			drm_gpuvm_bo_list_del(vm_bo, evict);
> > > > +	}
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_evict);
> > > > +
> > > >    static int
> > > >    __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> > > >    		   struct drm_gpuva *va)
> > > > diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> > > > index afa50b9059a2..834bb6d6617e 100644
> > > > --- a/include/drm/drm_gpuvm.h
> > > > +++ b/include/drm/drm_gpuvm.h
> > > > @@ -26,10 +26,12 @@
> > > >     */
> > > >    #include <linux/list.h>
> > > > +#include <linux/dma-resv.h>
> > > >    #include <linux/rbtree.h>
> > > >    #include <linux/types.h>
> > > >    #include <drm/drm_gem.h>
> > > > +#include <drm/drm_exec.h>
> > > >    struct drm_gpuvm;
> > > >    struct drm_gpuvm_bo;
> > > > @@ -259,6 +261,38 @@ struct drm_gpuvm {
> > > >    	 * space
> > > >    	 */
> > > >    	struct dma_resv *resv;
> > > > +
> > > > +	/**
> > > > +	 * @extobj: structure holding the extobj list
> > > > +	 */
> > > > +	struct {
> > > > +		/**
> > > > +		 * @list: &list_head storing &drm_gpuvm_bos serving as
> > > > +		 * external object
> > > > +		 */
> > > > +		struct list_head list;
> > > > +
> > > > +		/**
> > > > +		 * @lock: spinlock to protect the extobj list
> > > > +		 */
> > > > +		spinlock_t lock;
> > > > +	} extobj;
> > > > +
> > > > +	/**
> > > > +	 * @evict: structure holding the evict list and evict list lock
> > > > +	 */
> > > > +	struct {
> > > > +		/**
> > > > +		 * @list: &list_head storing &drm_gpuvm_bos currently being
> > > > +		 * evicted
> > > > +		 */
> > > > +		struct list_head list;
> > > > +
> > > > +		/**
> > > > +		 * @lock: spinlock to protect the evict list
> > > > +		 */
> > > > +		spinlock_t lock;
> > > > +	} evict;
> > > >    };
> > > >    void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_device *drm,
> > > > @@ -268,6 +302,21 @@ void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_device *drm,
> > > >    		    const struct drm_gpuvm_ops *ops);
> > > >    void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
> > > > +/**
> > > > + * drm_gpuvm_is_extobj() - indicates whether the given &drm_gem_object is an
> > > > + * external object
> > > > + * @gpuvm: the &drm_gpuvm to check
> > > > + * @obj: the &drm_gem_object to check
> > > > + *
> > > > + * Returns: true if the &drm_gem_object &dma_resv differs from the
> > > > + * &drm_gpuvms &dma_resv, false otherwise
> > > > + */
> > > > +static inline bool drm_gpuvm_is_extobj(struct drm_gpuvm *gpuvm,
> > > > +				       struct drm_gem_object *obj)
> > > > +{
> > > > +	return obj && obj->resv != gpuvm->resv;
> > > > +}
> > > > +
> > > >    static inline struct drm_gpuva *
> > > >    __drm_gpuva_next(struct drm_gpuva *va)
> > > >    {
> > > > @@ -346,6 +395,128 @@ __drm_gpuva_next(struct drm_gpuva *va)
> > > >    #define drm_gpuvm_for_each_va_safe(va__, next__, gpuvm__) \
> > > >    	list_for_each_entry_safe(va__, next__, &(gpuvm__)->rb.list, rb.entry)
> > > > +/**
> > > > + * struct drm_gpuvm_exec - &drm_gpuvm abstraction of &drm_exec
> > > > + *
> > > > + * This structure should be created on the stack as &drm_exec should be.
> > > > + *
> > > > + * Optionally, @extra can be set in order to lock additional &drm_gem_objects.
> > > > + */
> > > > +struct drm_gpuvm_exec {
> > > > +	/**
> > > > +	 * @exec: the &drm_exec structure
> > > > +	 */
> > > > +	struct drm_exec exec;
> > > > +
> > > > +	/**
> > > > +	 * @vm: the &drm_gpuvm to lock its DMA reservations
> > > > +	 */
> > > > +	struct drm_gpuvm *vm;
> > > > +
> > > > +	/**
> > > > +	 * @extra: Callback and corresponding private data for the driver to
> > > > +	 * lock arbitrary additional &drm_gem_objects.
> > > > +	 */
> > > > +	struct {
> > > > +		/**
> > > > +		 * @fn: The driver callback to lock additional &drm_gem_objects.
> > > > +		 */
> > > > +		int (*fn)(struct drm_gpuvm_exec *vm_exec,
> > > > +			  unsigned int num_fences);
> > > > +
> > > > +		/**
> > > > +		 * @priv: driver private data for the @fn callback
> > > > +		 */
> > > > +		void *priv;
> > > > +	} extra;
> > > > +};
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_prepare_vm() - prepare the GPUVMs common dma-resv
> > > > + * @gpuvm: the &drm_gpuvm
> > > > + * @exec: the &drm_exec context
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + *
> > > > + * Calls drm_exec_prepare_obj() for the GPUVMs dummy &drm_gem_object.
> > > > + *
> > > > + * Using this function directly, it is the drivers responsibility to call
> > > > + * drm_exec_init() and drm_exec_fini() accordingly.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +static inline int
> > > > +drm_gpuvm_prepare_vm(struct drm_gpuvm *gpuvm,
> > > > +		     struct drm_exec *exec,
> > > > +		     unsigned int num_fences)
> > > > +{
> > > > +	return drm_exec_prepare_obj(exec, &gpuvm->d_obj, num_fences);
> > > > +}
> > > > +
> > > > +int drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
> > > > +			      struct drm_exec *exec,
> > > > +			      unsigned int num_fences);
> > > > +
> > > > +int drm_gpuvm_prepare_range(struct drm_gpuvm *gpuvm,
> > > > +			    struct drm_exec *exec,
> > > > +			    u64 addr, u64 range,
> > > > +			    unsigned int num_fences);
> > > > +
> > > > +int drm_gpuvm_exec_lock(struct drm_gpuvm_exec *vm_exec,
> > > > +			unsigned int num_fences,
> > > > +			bool interruptible);
> > > > +
> > > > +int drm_gpuvm_exec_lock_array(struct drm_gpuvm_exec *vm_exec,
> > > > +			      struct drm_gem_object **objs,
> > > > +			      unsigned int num_objs,
> > > > +			      unsigned int num_fences,
> > > > +			      bool interruptible);
> > > > +
> > > > +int drm_gpuvm_exec_lock_range(struct drm_gpuvm_exec *vm_exec,
> > > > +			      u64 addr, u64 range,
> > > > +			      unsigned int num_fences,
> > > > +			      bool interruptible);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_lock() - lock all dma-resv of all assoiciated BOs
> > > > + * @gpuvm: the &drm_gpuvm
> > > > + *
> > > > + * Releases all dma-resv locks of all &drm_gem_objects previously acquired
> > > > + * through drm_gpuvm_lock() or its variants.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +static inline void
> > > > +drm_gpuvm_exec_unlock(struct drm_gpuvm_exec *vm_exec)
> > > > +{
> > > > +	drm_exec_fini(&vm_exec->exec);
> > > > +}
> > > > +
> > > > +int drm_gpuvm_validate(struct drm_gpuvm *gpuvm);
> > > > +void drm_gpuvm_resv_add_fence(struct drm_gpuvm *gpuvm,
> > > > +			      struct drm_exec *exec,
> > > > +			      struct dma_fence *fence,
> > > > +			      enum dma_resv_usage private_usage,
> > > > +			      enum dma_resv_usage extobj_usage);
> > > > +
> > > > +/**
> > > > + * drm_gpuvm_exec_resv_add_fence()
> > > > + * @vm_exec: the &drm_gpuvm_exec abstraction
> > > > + * @fence: fence to add
> > > > + * @private_usage: private dma-resv usage
> > > > + * @extobj_usage: extobj dma-resv usage
> > > > + *
> > > > + * See drm_gpuvm_resv_add_fence().
> > > > + */
> > > > +static inline void
> > > > +drm_gpuvm_exec_resv_add_fence(struct drm_gpuvm_exec *vm_exec,
> > > > +			      struct dma_fence *fence,
> > > > +			      enum dma_resv_usage private_usage,
> > > > +			      enum dma_resv_usage extobj_usage)
> > > > +{
> > > > +	drm_gpuvm_resv_add_fence(vm_exec->vm, &vm_exec->exec, fence,
> > > > +				 private_usage, extobj_usage);
> > > > +}
> > > > +
> > > >    /**
> > > >     * struct drm_gpuvm_bo - structure representing a &drm_gpuvm and
> > > >     * &drm_gem_object combination
> > > > @@ -398,6 +569,18 @@ struct drm_gpuvm_bo {
> > > >    			 * gpuva list.
> > > >    			 */
> > > >    			struct list_head gem;
> > > > +
> > > > +			/**
> > > > +			 * @evict: List entry to attach to the &drm_gpuvms
> > > > +			 * extobj list.
> > > > +			 */
> > > > +			struct list_head extobj;
> > > > +
> > > > +			/**
> > > > +			 * @evict: List entry to attach to the &drm_gpuvms evict
> > > > +			 * list.
> > > > +			 */
> > > > +			struct list_head evict;
> > > >    		} entry;
> > > >    	} list;
> > > >    };
> > > > @@ -432,6 +615,9 @@ struct drm_gpuvm_bo *
> > > >    drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> > > >    		  struct drm_gem_object *obj);
> > > > +void drm_gpuvm_bo_evict(struct drm_gem_object *obj, bool evict);
> > > > +void drm_gpuvm_bo_extobj_add(struct drm_gpuvm_bo *vm_bo);
> > > > +
> > > >    /**
> > > >     * drm_gpuvm_bo_for_each_va() - iterator to walk over a list of &drm_gpuva
> > > >     * @va__: &drm_gpuva structure to assign to in each iteration step
> > > > @@ -837,6 +1023,17 @@ struct drm_gpuvm_ops {
> > > >    	 * used.
> > > >    	 */
> > > >    	int (*sm_step_unmap)(struct drm_gpuva_op *op, void *priv);
> > > > +
> > > > +	/**
> > > > +	 * @bo_validate: called from drm_gpuvm_validate()
> > > > +	 *
> > > > +	 * Drivers receive this callback for every evicted &drm_gem_object being
> > > > +	 * mapped in the corresponding &drm_gpuvm.
> > > > +	 *
> > > > +	 * Typically, drivers would call their driver specific variant of
> > > > +	 * ttm_bo_validate() from within this callback.
> > > > +	 */
> > > > +	int (*bo_validate)(struct drm_gem_object *obj);
> > > >    };
> > > >    int drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm, void *priv,
>