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Date:   Tue, 12 Sep 2023 18:50:51 +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
Message-ID: <ZQCW6wzHYVdxl/IV@pollux>
References: <20230909153125.30032-1-dakr@redhat.com>
 <20230909153125.30032-7-dakr@redhat.com>
 <a9ef04d2-2525-65c0-2eda-45ca9a95a3a0@linux.intel.com>
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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.

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.

> 
> 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.

> 
> 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,
>