Message-ID: <9d2c3eb5-f0e6-23a6-0946-7d63670b4778@linux.intel.com>
Date:   Mon, 9 Oct 2023 15:36:58 +0200
From:   Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
To:     Danilo Krummrich <dakr@...hat.com>, airlied@...il.com,
        daniel@...ll.ch, matthew.brost@...el.com, sarah.walker@...tec.com,
        donald.robson@...tec.com, boris.brezillon@...labora.com,
        christian.koenig@....com, faith@...strand.net
Cc:     dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v6 4/6] drm/gpuvm: track/lock/validate
 external/evicted objects


On 10/9/23 01:32, Danilo Krummrich wrote:
> Currently the DRM GPUVM 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 GPUVM represent
> a basis for GPU-VM implementations. 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.
>
> Big thanks 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@...el.com>
> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> ---
>   drivers/gpu/drm/drm_gpuvm.c | 646 ++++++++++++++++++++++++++++++++++++
>   include/drm/drm_gpuvm.h     | 246 ++++++++++++++
>   2 files changed, 892 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
> index 28282283ddaf..6977bd30eca5 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -82,6 +82,21 @@
>    * &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, 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.
>    */
>   
>   /**
> @@ -429,6 +444,20 @@
>    * 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, namely drm_gpuvm_prepare_objects() and
> + * drm_gpuvm_validate().
> + *
> + * Alternatively, drivers can set the &DRM_GPUVM_RESV_PROTECTED flag to indicate
> + * that the corresponding &dma_resv locks are held in order to protect the
> + * lists. If &DRM_GPUVM_RESV_PROTECTED is set, internal locking is disabled and
> + * the corresponding lockdep checks are enabled. This is an optimization for
> + * drivers which are capable of taking the corresponding &dma_resv locks and
> + * hence do not require internal locking.
>    */
>   
>   /**
> @@ -641,6 +670,195 @@
>    *	}
>    */
>   
> +/**
> + * 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.
> + *
> + * 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 = NULL;					\
> +											\
> +		drm_gpuvm_bo_put(__prev_vm_bo);						\
> +											\
> +		spin_lock(&(__gpuvm)->__list_name.lock);				\
> +		if (!(__gpuvm)->__list_name.local_list)					\
> +			(__gpuvm)->__list_name.local_list = __local_list;		\
> +		else									\
> +			WARN_ON((__gpuvm)->__list_name.local_list != __local_list);	\
> +											\
> +		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 (kref_get_unless_zero(&__vm_bo->kref)) {			\
> +				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, hence list insertion and deletion can happen concurrently.
> + *
> + * It is not allowed to re-assign the vm_bo pointer from inside this loop.
> + *
> + * Typical use:
> + *
> + *	struct drm_gpuvm_bo *vm_bo;
> + *	LIST_HEAD(my_local_list);
> + *
> + *	ret = 0;
> + *	for_each_vm_bo_in_list(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);
> + *	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))
> +
> +static void
> +__restore_vm_bo_list(struct drm_gpuvm *gpuvm, spinlock_t *lock,
> +		     struct list_head *list, struct list_head **local_list)
> +{
> +	/* Merge back the two lists, moving local list elements to the
> +	 * head to preserve previous ordering, in case it matters.
> +	 */
> +	spin_lock(lock);
> +	if (*local_list) {
> +		list_splice(*local_list, list);
> +		*local_list = NULL;
> +	}
> +	spin_unlock(lock);
> +}
> +
> +/**
> + * 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
> + *
> + * 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)			\
> +	__restore_vm_bo_list((__gpuvm), &(__gpuvm)->__list_name.lock,	\
> +			     &(__gpuvm)->__list_name.list,		\
> +			     &(__gpuvm)->__list_name.local_list)
> +
> +static void
> +cond_spin_lock(spinlock_t *lock, bool cond)
> +{
> +	if (cond)
> +		spin_lock(lock);
> +}
> +
> +static void
> +cond_spin_unlock(spinlock_t *lock, bool cond)
> +{
> +	if (cond)
> +		spin_unlock(lock);
> +}
> +
> +static void
> +__drm_gpuvm_bo_list_add(struct drm_gpuvm *gpuvm, spinlock_t *lock,
> +			struct list_head *entry, struct list_head *list)
> +{
> +	cond_spin_lock(lock, !!lock);
> +	if (list_empty(entry))
> +		list_add_tail(entry, list);
> +	cond_spin_unlock(lock, !!lock);
> +}
> +
> +/**
> + * 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
> + * @__lock: whether to lock with the internal spinlock
> + *
> + * Inserts the given @__vm_bo into the list specified by @__list_name.
> + */
> +#define drm_gpuvm_bo_list_add(__vm_bo, __list_name, __lock)			\
> +	__drm_gpuvm_bo_list_add((__vm_bo)->vm,					\
> +				__lock ? &(__vm_bo)->vm->__list_name.lock :	\
> +					 NULL,					\
> +				&(__vm_bo)->list.entry.__list_name,		\
> +				&(__vm_bo)->vm->__list_name.list)
> +
> +static void
> +__drm_gpuvm_bo_list_del(struct drm_gpuvm *gpuvm, spinlock_t *lock,
> +			struct list_head *entry, bool init)
> +{
> +	cond_spin_lock(lock, !!lock);
> +	if (init) {
> +		if (!list_empty(entry))
> +			list_del_init(entry);
> +	} else {
> +		list_del(entry);
> +	}
> +	cond_spin_unlock(lock, !!lock);
> +}
> +
> +/**
> + * drm_gpuvm_bo_list_del_init() - remove a vm_bo from the given list
> + * @__vm_bo: the &drm_gpuvm_bo
> + * @__list_name: the name of the list to insert into
> + * @__lock: whether to lock with the internal spinlock
> + *
> + * Removes the given @__vm_bo from the list specified by @__list_name.
> + */
> +#define drm_gpuvm_bo_list_del_init(__vm_bo, __list_name, __lock)		\
> +	__drm_gpuvm_bo_list_del((__vm_bo)->vm,					\
> +				__lock ? &(__vm_bo)->vm->__list_name.lock :	\
> +					 NULL,					\
> +				&(__vm_bo)->list.entry.__list_name,		\
> +				true)
> +
> +/**
> + * 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
> + * @__lock: whether to lock with the internal spinlock
> + *
> + * Removes the given @__vm_bo from the list specified by @__list_name.
> + */
> +#define drm_gpuvm_bo_list_del(__vm_bo, __list_name, __lock)			\
> +	__drm_gpuvm_bo_list_del((__vm_bo)->vm,					\
> +				__lock ? &(__vm_bo)->vm->__list_name.lock :	\
> +					 NULL,					\
> +				&(__vm_bo)->list.entry.__list_name,		\
> +				false)
> +
>   #define to_drm_gpuva(__node)	container_of((__node), struct drm_gpuva, rb.node)
>   
>   #define GPUVA_START(node) ((node)->va.addr)
> @@ -760,6 +978,12 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_gem_object *r_obj,
>   	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_gpuvm_check_overflow(start_offset, range);
>   	gpuvm->mm_start = start_offset;
>   	gpuvm->mm_range = range;
> @@ -802,10 +1026,372 @@ 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_object_put(gpuvm->r_obj);
>   }
>   EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
>   
> +static 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);
> +
> +	return ret;
> +}
> +
> +static int
> +drm_gpuvm_prepare_objects_locked(struct drm_gpuvm *gpuvm,
> +				 struct drm_exec *exec,
> +				 unsigned int num_fences)
> +{
> +	struct drm_gpuvm_bo *vm_bo;
> +	int ret = 0;
> +
> +	drm_gpuvm_resv_assert_held(gpuvm);
> +	list_for_each_entry(vm_bo, &gpuvm->extobj.list, list.entry.extobj) {
> +		ret = drm_exec_prepare_obj(exec, vm_bo->obj, num_fences);
> +		if (ret)
> +			break;
> +
> +		if (vm_bo->evicted)
> +			drm_gpuvm_bo_list_add(vm_bo, evict, false);

Clear vm_bo->evicted here?


> +	}
> +
> +	return ret;
> +}
> +
> +/**
> + * 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)
> +{
> +	if (drm_gpuvm_resv_protected(gpuvm))
> +		return drm_gpuvm_prepare_objects_locked(gpuvm, exec,
> +							num_fences);
> +	else
> +		return __drm_gpuvm_prepare_objects(gpuvm, exec, num_fences);
> +
> +}
> +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 wrapper
> + * @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 wrapper
> + * @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 wrapper
> + * @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);
> +
> +static int
> +__drm_gpuvm_validate(struct drm_gpuvm *gpuvm, struct drm_exec *exec)
> +{
> +	const struct drm_gpuvm_ops *ops = gpuvm->ops;
> +	struct drm_gpuvm_bo *vm_bo;
> +	LIST_HEAD(evict);
> +	int ret = 0;
> +
> +	for_each_vm_bo_in_list(gpuvm, evict, &evict, vm_bo) {
> +		ret = ops->vm_bo_validate(vm_bo, exec);
> +		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);
> +
> +	return ret;
> +}
> +
> +static int
> +drm_gpuvm_validate_locked(struct drm_gpuvm *gpuvm, struct drm_exec *exec)
> +{
> +	const struct drm_gpuvm_ops *ops = gpuvm->ops;
> +	struct drm_gpuvm_bo *vm_bo, *next;
> +	int ret = 0;
> +
> +	drm_gpuvm_resv_assert_held(gpuvm);
> +
> +	/* Iterate list safely, drivers typically remove the current entry from
> +	 * their drm_gpuvm_ops::vm_bo_validate callback. Drivers might also
> +	 * re-add the entry on failure; this is safe since on failure we break
> +	 * out of the loop.
> +	 */
> +	list_for_each_entry_safe(vm_bo, next, &gpuvm->evict.list,
> +				 list.entry.evict) {
> +		ret = ops->vm_bo_validate(vm_bo, exec);
> +		if (ret)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +
> +/**
> + * drm_gpuvm_validate() - validate all BOs marked as evicted
> + * @gpuvm: the &drm_gpuvm to validate evicted BOs
> + * @exec: the &drm_exec instance used for locking the GPUVM
> + *
> + * Calls the &drm_gpuvm_ops::vm_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, struct drm_exec *exec)
> +{
> +	const struct drm_gpuvm_ops *ops = gpuvm->ops;
> +
> +	if (unlikely(!ops || !ops->vm_bo_validate))
> +		return -ENOTSUPP;
> +
> +	if (drm_gpuvm_resv_protected(gpuvm))
> +		return drm_gpuvm_validate_locked(gpuvm, exec);
> +	else
> +		return __drm_gpuvm_validate(gpuvm, exec);
> +
> +}
> +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.
> @@ -838,6 +1424,9 @@ 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;
> @@ -858,6 +1447,9 @@ drm_gpuvm_bo_destroy(struct kref *kref)
>   	if (!lock)
>   		drm_gpuvm_resv_assert_held(gpuvm);
>   
> +	drm_gpuvm_bo_list_del(vm_bo, extobj, lock);
> +	drm_gpuvm_bo_list_del(vm_bo, evict, lock);
> +
>   	list_del(&vm_bo->list.entry.gem);
>   
>   	drm_gem_object_put(obj);
> @@ -994,6 +1586,60 @@ 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;
> +	bool lock = !drm_gpuvm_resv_protected(gpuvm);
> +
> +	if (!lock)
> +		drm_gpuvm_resv_assert_held(gpuvm);
> +
> +	if (drm_gpuvm_is_extobj(gpuvm, vm_bo->obj))
> +		drm_gpuvm_bo_list_add(vm_bo, extobj, lock);
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_extobj_add);
> +
> +/**
> + * drm_gpuvm_bo_evict() - add / remove a &drm_gpuvm_bo to / from the &drm_gpuvms
> + * evicted list
> + * @vm_bo: the &drm_gpuvm_bo to add or remove
> + * @evict: indicates whether the object is evicted
> + *
> + * Adds a &drm_gpuvm_bo to or removes it from the &drm_gpuvms evicted list.
> + */
> +void
> +drm_gpuvm_bo_evict(struct drm_gpuvm_bo *vm_bo, bool evict)
> +{
> +	struct drm_gpuvm *gpuvm = vm_bo->vm;
> +	struct drm_gem_object *obj = vm_bo->obj;
> +	bool lock = !drm_gpuvm_resv_protected(gpuvm);
> +
> +	dma_resv_assert_held(obj->resv);
> +
> +	if (drm_gpuvm_is_extobj(gpuvm, obj)) {
> +		vm_bo->evicted = evict;
Does the lock case also need this?
> +
> +		if (!lock)
> +			return;

Here the !lock case can not remove the gpuvm_bo from the list?

Small patch here that I've been using for xe:

https://patchwork.freedesktop.org/patch/561545/?series=124817&rev=1

Thanks,

Thomas

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