Re: [PATCH drm-misc-next 2/3] drm/gpuva_mgr: generalize dma_resv/extobj handling and GEM validation
From: Danilo Krummrich
Date: Wed Aug 30 2023 - 14:54:13 EST
On Wed, Aug 30, 2023 at 03:42:08PM +0200, Thomas Hellström (Intel) wrote:
>
> On 8/30/23 14:49, Danilo Krummrich wrote:
> > Hi Thomas,
> >
> > thanks for having a look!
> >
> > On Wed, Aug 30, 2023 at 09:27:45AM +0200, Thomas Hellström (Intel) wrote:
> > > Hi, Danilo.
> > >
> > > Some quick comments since I'm doing some Xe work in this area. Will probably
> > > get back with more.
> > >
> > > On 8/20/23 23:53, 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.
> > > >
> > > > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > > > ---
> > > > drivers/gpu/drm/drm_gpuva_mgr.c | 688 +++++++++++++++++++++++++++++++-
> > > > include/drm/drm_gem.h | 48 ++-
> > > > include/drm/drm_gpuva_mgr.h | 302 +++++++++++++-
> > > > 3 files changed, 1010 insertions(+), 28 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_gpuva_mgr.c b/drivers/gpu/drm/drm_gpuva_mgr.c
> > > > index f86bfad74ff8..69872b205961 100644
> > > > --- a/drivers/gpu/drm/drm_gpuva_mgr.c
> > > > +++ b/drivers/gpu/drm/drm_gpuva_mgr.c
> > > > @@ -655,6 +655,7 @@ drm_gpuva_range_valid(struct drm_gpuva_manager *mgr,
> > > > /**
> > > > * drm_gpuva_manager_init() - initialize a &drm_gpuva_manager
> > > > * @mgr: pointer to the &drm_gpuva_manager to initialize
> > > > + * @drm: the drivers &drm_device
> > > > * @name: the name of the GPU VA space
> > > > * @start_offset: the start offset of the GPU VA space
> > > > * @range: the size of the GPU VA space
> > > > @@ -669,6 +670,7 @@ drm_gpuva_range_valid(struct drm_gpuva_manager *mgr,
> > > > */
> > > > void
> > > > drm_gpuva_manager_init(struct drm_gpuva_manager *mgr,
> > > > + struct drm_device *drm,
> > > > const char *name,
> > > > u64 start_offset, u64 range,
> > > > u64 reserve_offset, u64 reserve_range,
> > > > @@ -677,6 +679,11 @@ drm_gpuva_manager_init(struct drm_gpuva_manager *mgr,
> > > > mgr->rb.tree = RB_ROOT_CACHED;
> > > > INIT_LIST_HEAD(&mgr->rb.list);
> > > > + mt_init(&mgr->mt_ext);
> > > > +
> > > > + INIT_LIST_HEAD(&mgr->evict.list);
> > > > + spin_lock_init(&mgr->evict.lock);
> > > > +
> > > > drm_gpuva_check_overflow(start_offset, range);
> > > > mgr->mm_start = start_offset;
> > > > mgr->mm_range = range;
> > > > @@ -694,6 +701,9 @@ drm_gpuva_manager_init(struct drm_gpuva_manager *mgr,
> > > > reserve_range)))
> > > > __drm_gpuva_insert(mgr, &mgr->kernel_alloc_node);
> > > > }
> > > > +
> > > > + drm_gem_private_object_init(drm, &mgr->d_obj, 0);
> > > > + mgr->resv = mgr->d_obj.resv;
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_manager_init);
> > > > @@ -713,10 +723,575 @@ drm_gpuva_manager_destroy(struct drm_gpuva_manager *mgr)
> > > > __drm_gpuva_remove(&mgr->kernel_alloc_node);
> > > > WARN(!RB_EMPTY_ROOT(&mgr->rb.tree.rb_root),
> > > > - "GPUVA tree is not empty, potentially leaking memory.");
> > > > + "GPUVA tree is not empty, potentially leaking memory.\n");
> > > > +
> > > > + mtree_destroy(&mgr->mt_ext);
> > > > + WARN(!list_empty(&mgr->evict.list), "Evict list should be empty.\n");
> > > > +
> > > > + drm_gem_private_object_fini(&mgr->d_obj);
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_manager_destroy);
> > > > +/**
> > > > + * drm_gpuva_manager_prepare_objects() - prepare all assoiciated BOs
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > + *
> > > > + * Calls drm_exec_prepare_obj() for all &drm_gem_objects the given
> > > > + * &drm_gpuva_manager contains mappings of.
> > > > + *
> > > > + * Drivers can obtain the corresponding &drm_exec instance through
> > > > + * DRM_GPUVA_EXEC(). It is the drivers responsibility to call drm_exec_init()
> > > > + * and drm_exec_fini() accordingly.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuva_manager_prepare_objects(struct drm_gpuva_manager *mgr,
> > > > + unsigned int num_fences)
> > > > +{
> > > > + struct drm_exec *exec = DRM_GPUVA_EXEC(mgr);
> > > > + MA_STATE(mas, &mgr->mt_ext, 0, 0);
> > > > + union {
> > > > + void *ptr;
> > > > + uintptr_t cnt;
> > > > + } ref;
> > > > + int ret;
> > > > +
> > > > + ret = drm_exec_prepare_obj(exec, &mgr->d_obj, num_fences);
> > > > + if (ret)
> > > > + goto out;
> > > > +
> > > > + rcu_read_lock();
> > > In xe we're protecting the external object list with an outer lock, (same as
> > > protecting the mgr itself). Do we need a separate lock for this? In theory
> > > as outlined in the VM_BIND locking document draft, one could probably even
> > > use the mgr resv for this, but with more complicated code I guess. Also see
> > > the comment below about the data structure chosen.
> > The idea is to protect this list with the GPU-VM lock. The locking here is more
> > of an implication of the maple tree. Either you use the internal lock of the
> > maple tree or RCU respectively, or you give the maple tree an external lock to
> > perform lockdep checks on (mt_set_external_lock()). Basically same as here:
> >
> > https://elixir.bootlin.com/linux/latest/source/drivers/base/regmap/regcache-maple.c#L124
>
> Ah, I suspected it was something along those lines.
>
>
> >
> > > > + mas_for_each(&mas, ref.ptr, ULONG_MAX) {
> > > > + struct drm_gem_object *obj;
> > > > +
> > > > + mas_pause(&mas);
> > > > + rcu_read_unlock();
> > > > +
> > > > + obj = (struct drm_gem_object *)(uintptr_t)mas.index;
> > > > + ret = drm_exec_prepare_obj(exec, obj, num_fences);
> > > > + if (ret)
> > > > + goto out;
> > > > +
> > > > + rcu_read_lock();
> > > > + }
> > > > + rcu_read_unlock();
> > > > +
> > > > +out:
> > > > + return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_manager_prepare_objects);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_lock_extra() - lock all dma-resv of all assoiciated BOs
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + * @fn: callback received by the driver to lock additional dma-resv
> > > > + * @priv: private driver data passed to @fn
> > > > + * @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_gpuva_manager contains mappings of.
> > > > + *
> > > > + * Addionally, when calling this function the driver receives the given @fn
> > > > + * callback to lock additional dma-resv in the context of the
> > > > + * &drm_gpuva_managers &drm_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_gpuva_manager_lock_extra(struct drm_gpuva_manager *mgr,
> > > > + int (*fn)(struct drm_gpuva_manager *mgr,
> > > > + void *priv, unsigned int num_fences),
> > > > + void *priv,
> > > > + unsigned int num_fences,
> > > > + bool interruptible)
> > > > +{
> > > > + struct drm_exec *exec = DRM_GPUVA_EXEC(mgr);
> > > > + 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_gpuva_manager_prepare_objects(mgr, num_fences);
> > > > + drm_exec_retry_on_contention(exec);
> > > > + if (ret)
> > > > + goto err;
> > > > +
> > > > + if (fn) {
> > > > + ret = fn(mgr, priv, 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_gpuva_manager_lock_extra);
> > > > +
> > > > +static int
> > > > +fn_lock_array(struct drm_gpuva_manager *mgr, void *priv,
> > > > + unsigned int num_fences)
> > > > +{
> > > > + struct {
> > > > + struct drm_gem_object **objs;
> > > > + unsigned int num_objs;
> > > > + } *args = priv;
> > > > +
> > > > + return drm_exec_prepare_array(DRM_GPUVA_EXEC(mgr), args->objs,
> > > > + args->num_objs, num_fences);
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_lock_array() - lock all dma-resv of all assoiciated BOs
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + * @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_gpuva_manager contains mappings of, plus the ones given through @objs.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuva_manager_lock_array(struct drm_gpuva_manager *mgr,
> > > > + 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;
> > > > +
> > > > + return drm_gpuva_manager_lock_extra(mgr, fn_lock_array, &args,
> > > > + num_fences, interruptible);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_manager_lock_array);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_validate() - validate all BOs marked as evicted
> > > > + * @mgr: the &drm_gpuva_manager to validate evicted BOs
> > > > + *
> > > > + * Calls the &drm_gpuva_fn_ops.bo_validate callback for all evicted buffer
> > > > + * objects being mapped in the given &drm_gpuva_manager.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuva_manager_validate(struct drm_gpuva_manager *mgr)
> > > > +{
> > > > + const struct drm_gpuva_fn_ops *ops = mgr->ops;
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > + int ret;
> > > > +
> > > > + if (unlikely(!ops || !ops->bo_validate))
> > > > + return -ENOTSUPP;
> > > > +
> > > > + /* At this point we should hold all dma-resv locks of all GEM objects
> > > > + * associated with this GPU-VM, hence it is safe to walk the list.
> > > > + */
> > > > + list_for_each_entry(vm_bo, &mgr->evict.list, list.entry.evict) {
> > > > + dma_resv_assert_held(vm_bo->obj->resv);
> > > > +
> > > > + ret = ops->bo_validate(vm_bo->obj);
> > > > + if (ret)
> > > > + return ret;
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_manager_validate);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_resv_add_fence - add fence to private and all extobj
> > > > + * dma-resv
> > > > + * @mgr: the &drm_gpuva_manager to add a fence to
> > > > + * @fence: fence to add
> > > > + * @private_usage: private dma-resv usage
> > > > + * @extobj_usage: extobj dma-resv usage
> > > > + */
> > > > +void
> > > > +drm_gpuva_manager_resv_add_fence(struct drm_gpuva_manager *mgr,
> > > > + struct dma_fence *fence,
> > > > + enum dma_resv_usage private_usage,
> > > > + enum dma_resv_usage extobj_usage)
> > > > +{
> > > > + struct drm_exec *exec = DRM_GPUVA_EXEC(mgr);
> > > > + 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_gpuva_is_extobj(mgr, obj) ?
> > > > + private_usage : extobj_usage);
> > > > + }
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_manager_resv_add_fence);
> > > > +
> > > > +static struct drm_gpuva_gem *
> > > > +__drm_gpuva_gem_find(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > +
> > > > + drm_gem_gpuva_assert_lock_held(obj);
> > > > +
> > > > + drm_gem_for_each_gpuva_gem(vm_bo, obj)
> > > > + if (vm_bo->mgr == mgr)
> > > > + return vm_bo;
> > > > +
> > > > + return NULL;
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_create() - create a new instance of struct drm_gpuva_gem
> > > > + * @mgr: The &drm_gpuva_manager the @obj is mapped in.
> > > > + * @obj: The &drm_gem_object being mapped in the @mgr.
> > > > + *
> > > > + * If provided by the driver, this function uses the &drm_gpuva_fn_ops
> > > > + * vm_bo_alloc() callback to allocate.
> > > > + *
> > > > + * Returns: a pointer to the &drm_gpuva_gem on success, NULL on failure
> > > > + */
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_create(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + const struct drm_gpuva_fn_ops *ops = mgr->ops;
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > +
> > > > + if (ops && ops->vm_bo_alloc)
> > > > + vm_bo = ops->vm_bo_alloc();
> > > > + else
> > > > + vm_bo = kzalloc(sizeof(*vm_bo), GFP_KERNEL);
> > > > +
> > > > + if (unlikely(!vm_bo))
> > > > + return NULL;
> > > > +
> > > > + vm_bo->mgr = mgr;
> > > > + vm_bo->obj = obj;
> > > > +
> > > > + kref_init(&vm_bo->kref);
> > > > + INIT_LIST_HEAD(&vm_bo->list.gpuva);
> > > > + INIT_LIST_HEAD(&vm_bo->list.entry.gem);
> > > > + INIT_LIST_HEAD(&vm_bo->list.entry.evict);
> > > > +
> > > > + drm_gem_object_get(obj);
> > > > +
> > > > + return vm_bo;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_create);
> > > > +
> > > > +void
> > > > +drm_gpuva_gem_destroy(struct kref *kref)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo = container_of(kref, struct drm_gpuva_gem,
> > > > + kref);
> > > > + const struct drm_gpuva_fn_ops *ops = vm_bo->mgr->ops;
> > > > +
> > > > + drm_gem_object_put(vm_bo->obj);
> > > > +
> > > > + if (ops && ops->vm_bo_free)
> > > > + ops->vm_bo_free(vm_bo);
> > > > + else
> > > > + kfree(vm_bo);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_destroy);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_find() - find the &drm_gpuva_gem for the given
> > > > + * &drm_gpuva_manager and &drm_gem_object
> > > > + * @mgr: The &drm_gpuva_manager the @obj is mapped in.
> > > > + * @obj: The &drm_gem_object being mapped in the @mgr.
> > > > + *
> > > > + * Find the &drm_gpuva_gem representing the combination of the given
> > > > + * &drm_gpuva_manager and &drm_gem_object. If found, increases the reference
> > > > + * count of the &drm_gpuva_gem accordingly.
> > > > + *
> > > > + * Returns: a pointer to the &drm_gpuva_gem on success, NULL on failure
> > > > + */
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_find(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo = __drm_gpuva_gem_find(mgr, obj);
> > > > +
> > > > + return vm_bo ? drm_gpuva_gem_get(vm_bo) : NULL;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_find);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_obtain() - obtains and instance of the &drm_gpuva_gem for the
> > > > + * given &drm_gpuva_manager and &drm_gem_object
> > > > + * @mgr: The &drm_gpuva_manager the @obj is mapped in.
> > > > + * @obj: The &drm_gem_object being mapped in the @mgr.
> > > > + *
> > > > + * Find the &drm_gpuva_gem representing the combination of the given
> > > > + * &drm_gpuva_manager and &drm_gem_object. If found, increases the reference
> > > > + * count of the &drm_gpuva_gem accordingly. If not found, allsocates a new
> > > > + * &drm_gpuva_gem.
> > > > + *
> > > > + * Returns: a pointer to the &drm_gpuva_gem on success, an ERR_PTR on failure
> > > > + */
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_obtain(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > +
> > > > + vm_bo = drm_gpuva_gem_find(mgr, obj);
> > > > + if (vm_bo)
> > > > + return vm_bo;
> > > > +
> > > > + vm_bo = drm_gpuva_gem_create(mgr, obj);
> > > > + if (!vm_bo)
> > > > + return ERR_PTR(-ENOMEM);
> > > > +
> > > > + return vm_bo;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_obtain);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_obtain_prealloc() - obtains and instance of the &drm_gpuva_gem
> > > > + * for the given &drm_gpuva_manager and &drm_gem_object
> > > > + * @mgr: The &drm_gpuva_manager the @obj is mapped in.
> > > > + * @obj: The &drm_gem_object being mapped in the @mgr.
> > > > + *
> > > > + * Find the &drm_gpuva_gem representing the combination of the given
> > > > + * &drm_gpuva_manager and &drm_gem_object. If found, increases the reference
> > > > + * count of the found &drm_gpuva_gem accordingly, while the @__vm_bo reference
> > > > + * count is decreased. If not found @__vm_bo is returned.
> > > > + *
> > > > + * Returns: a pointer to the found &drm_gpuva_gem or @__vm_bo if no existing
> > > > + * &drm_gpuva_gem was found
> > > > + */
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_obtain_prealloc(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj,
> > > > + struct drm_gpuva_gem *__vm_bo)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > +
> > > > + vm_bo = drm_gpuva_gem_find(mgr, obj);
> > > > + if (vm_bo) {
> > > > + drm_gpuva_gem_put(__vm_bo);
> > > > + return vm_bo;
> > > > + }
> > > > +
> > > > + return __vm_bo;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_obtain_prealloc);
> > > > +
> > > > +static int
> > > > +__drm_gpuva_extobj_insert(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj,
> > > > + gfp_t gfp)
> > > > +{
> > > > + MA_STATE(mas, &mgr->mt_ext, 0, 0);
> > > > + union {
> > > > + struct drm_gem_object *obj;
> > > > + uintptr_t index;
> > > > + } gem;
> > > > + union {
> > > > + void *ptr;
> > > > + uintptr_t cnt;
> > > > + } ref;
> > > > + int ret = 0;
> > > > +
> > > > + gem.obj = obj;
> > > > + mas_set(&mas, gem.index);
> > > > +
> > > > + mas_lock(&mas);
> > > > + ref.ptr = mas_walk(&mas);
> > > > + if (ref.ptr) {
> > > > + ++ref.cnt;
> > > > + mas_store(&mas, ref.ptr);
> > > > + } else {
> > > > + if (unlikely(!gfp)) {
> > > > + ret = -EINVAL;
> > > > + goto out;
> > > > + }
> > > > +
> > > > + mas_set(&mas, gem.index);
> > > > + ref.cnt = 1;
> > > > + ret = mas_store_gfp(&mas, ref.ptr, gfp);
> > > > + if (likely(!ret))
> > > > + drm_gem_object_get(obj);
> > > > + }
> > > > +out:
> > > > + mas_unlock(&mas);
> > > > + return ret;
> > > > +}
> > > > +
> > > > +static void
> > > > +__drm_gpuva_extobj_remove(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + MA_STATE(mas, &mgr->mt_ext, 0, 0);
> > > > + union {
> > > > + struct drm_gem_object *obj;
> > > > + uintptr_t index;
> > > > + } gem;
> > > > + union {
> > > > + void *ptr;
> > > > + uintptr_t cnt;
> > > > + } ref;
> > > > +
> > > > + gem.obj = obj;
> > > > + mas_set(&mas, gem.index);
> > > > +
> > > > + mas_lock(&mas);
> > > > + if (unlikely(!(ref.ptr = mas_walk(&mas))))
> > > > + goto out;
> > > > +
> > > > + if (!--ref.cnt) {
> > > > + mas_erase(&mas);
> > > > + drm_gem_object_put(obj);
> > > > + } else {
> > > > + mas_store(&mas, ref.ptr);
> > > > + }
> > > > +out:
> > > > + mas_unlock(&mas);
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_extobj_insert - insert an external &drm_gem_object
> > > > + * @mgr: the &drm_gpuva_manager to insert into
> > > > + * @obj: the &drm_gem_object to insert as extobj
> > > > + *
> > > > + * Insert a &drm_gem_object into the &drm_gpuva_managers external object tree.
> > > > + * If the &drm_gem_object already exists in the tree, the reference counter
> > > > + * of this external object is increased by one.
> > > > + *
> > > > + * Drivers should insert the external &drm_gem_object before the dma-fence
> > > > + * signalling critical section, e.g. when submitting the job, and before
> > > > + * locking all &drm_gem_objects of a GPU-VM, e.g. with drm_gpuva_manager_lock()
> > > > + * or its dervates.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +int
> > > > +drm_gpuva_extobj_insert(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + return drm_gpuva_is_extobj(mgr, obj) ?
> > > > + __drm_gpuva_extobj_insert(mgr, obj, GFP_KERNEL) : 0;
> > > > +
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_extobj_insert);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_extobj_get - increase the referecne count of an external
> > > > + * &drm_gem_object
> > > > + * @mgr: the &drm_gpuva_manager storing the extobj
> > > > + * @obj: the &drm_gem_object to representing the extobj
> > > > + *
> > > > + * Increases the reference count of the extobj represented by @obj.
> > > > + *
> > > > + * Drivers should call this for every &drm_gpuva backed by a &drm_gem_object
> > > > + * being inserted.
> > > > + *
> > > > + * For &drm_gpuva_op_remap operations drivers should make sure to only take an
> > > > + * additional reference if the re-map operation splits an existing &drm_gpuva
> > > > + * into two separate ones.
> > > > + *
> > > > + * See also drm_gpuva_map_get() and drm_gpuva_remap_get().
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +void
> > > > +drm_gpuva_extobj_get(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + if (drm_gpuva_is_extobj(mgr, obj))
> > > > + WARN(__drm_gpuva_extobj_insert(mgr, obj, 0),
> > > > + "Can't increase ref-count of non-existent extobj.");
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_extobj_get);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_extobj_put - decrease the referecne count of an external
> > > > + * &drm_gem_object
> > > > + * @mgr: the &drm_gpuva_manager storing the extobj
> > > > + * @obj: the &drm_gem_object to representing the extobj
> > > > + *
> > > > + * Decreases the reference count of the extobj represented by @obj.
> > > > + *
> > > > + * Drivers should call this for every &drm_gpuva backed by a &drm_gem_object
> > > > + * being removed from the GPU VA space.
> > > > + *
> > > > + * See also drm_gpuva_unmap_put().
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +void
> > > > +drm_gpuva_extobj_put(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + if (drm_gpuva_is_extobj(mgr, obj))
> > > > + __drm_gpuva_extobj_remove(mgr, obj);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_extobj_put);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_evict() - add / remove a &drm_gem_object to / from a
> > > > + * &drm_gpuva_managers 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_gpuva_managers evicted
> > > > + * list containing a mapping of this &drm_gem_object.
> > > > + */
> > > > +void
> > > > +drm_gpuva_gem_evict(struct drm_gem_object *obj, bool evict)
> > > > +{
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > +
> > > > + /* Required for iterating the GEMs GPUVA GEM list. If no driver specific
> > > > + * lock has been set, the list is protected with the GEMs dma-resv lock.
> > > > + */
> > > > + drm_gem_gpuva_assert_lock_held(obj);
> > > > +
> > > > + /* Required to protect the GPUVA managers evict list against concurrent
> > > > + * access through drm_gpuva_manager_validate(). Concurrent insertions to
> > > > + * the evict list through different GEM object evictions are protected
> > > > + * by the GPUVA managers evict lock.
> > > > + */
> > > > + dma_resv_assert_held(obj->resv);
> > > > +
> > > > + drm_gem_for_each_gpuva_gem(vm_bo, obj) {
> > > > + struct drm_gpuva_manager *mgr = vm_bo->mgr;
> > > > +
> > > > + spin_lock(&mgr->evict.lock);
> > > > + if (evict)
> > > > + list_add_tail(&vm_bo->list.entry.evict,
> > > > + &mgr->evict.list);
> > > > + else
> > > > + list_del_init(&vm_bo->list.entry.evict);
> > > > + spin_unlock(&mgr->evict.lock);
> > > > + }
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_gem_evict);
> > > > +
> > > > static int
> > > > __drm_gpuva_insert(struct drm_gpuva_manager *mgr,
> > > > struct drm_gpuva *va)
> > > > @@ -806,15 +1381,20 @@ EXPORT_SYMBOL_GPL(drm_gpuva_remove);
> > > > /**
> > > > * drm_gpuva_link() - link a &drm_gpuva
> > > > * @va: the &drm_gpuva to link
> > > > + * @vm_bo: the &drm_gpuva_gem to add the &drm_gpuva to
> > > > *
> > > > - * This adds the given &va to the GPU VA list of the &drm_gem_object it is
> > > > - * associated with.
> > > > + * This adds the given &va to the GPU VA list of the &drm_gpuva_gem and the
> > > > + * &drm_gpuva_gem to the &drm_gem_object it is associated with.
> > > > + *
> > > > + * For every &drm_gpuva entry added to the &drm_gpuva_gem an additional
> > > > + * reference of the latter is taken.
> > > > *
> > > > * This function expects the caller to protect the GEM's GPUVA list against
> > > > - * concurrent access using the GEMs dma_resv lock.
> > > > + * concurrent access using either the GEMs dma_resv lock or a driver specific
> > > > + * lock set through drm_gem_gpuva_set_lock().
> > > > */
> > > > void
> > > > -drm_gpuva_link(struct drm_gpuva *va)
> > > > +drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuva_gem *vm_bo)
> > > > {
> > > > struct drm_gem_object *obj = va->gem.obj;
> > > > @@ -823,7 +1403,10 @@ drm_gpuva_link(struct drm_gpuva *va)
> > > > drm_gem_gpuva_assert_lock_held(obj);
> > > > - list_add_tail(&va->gem.entry, &obj->gpuva.list);
> > > > + drm_gpuva_gem_get(vm_bo);
> > > > + list_add_tail(&va->gem.entry, &vm_bo->list.gpuva);
> > > > + if (list_empty(&vm_bo->list.entry.gem))
> > > > + list_add_tail(&vm_bo->list.entry.gem, &obj->gpuva.list);
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_link);
> > > > @@ -834,20 +1417,39 @@ EXPORT_SYMBOL_GPL(drm_gpuva_link);
> > > > * This removes the given &va from the GPU VA list of the &drm_gem_object it is
> > > > * associated with.
> > > > *
> > > > + * This removes the given &va from the GPU VA list of the &drm_gpuva_gem and
> > > > + * the &drm_gpuva_gem from the &drm_gem_object it is associated with in case
> > > > + * this call unlinks the last &drm_gpuva from the &drm_gpuva_gem.
> > > > + *
> > > > + * For every &drm_gpuva entry removed from the &drm_gpuva_gem a reference of
> > > > + * the latter is dropped.
> > > > + *
> > > > * This function expects the caller to protect the GEM's GPUVA list against
> > > > - * concurrent access using the GEMs dma_resv lock.
> > > > + * concurrent access using either the GEMs dma_resv lock or a driver specific
> > > > + * lock set through drm_gem_gpuva_set_lock().
> > > > */
> > > > void
> > > > drm_gpuva_unlink(struct drm_gpuva *va)
> > > > {
> > > > struct drm_gem_object *obj = va->gem.obj;
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > if (unlikely(!obj))
> > > > return;
> > > > drm_gem_gpuva_assert_lock_held(obj);
> > > > + vm_bo = __drm_gpuva_gem_find(va->mgr, obj);
> > > > + if (WARN(!vm_bo, "GPUVA doesn't seem to be linked.\n"))
> > > > + return;
> > > > +
> > > > list_del_init(&va->gem.entry);
> > > > +
> > > > + if (list_empty(&vm_bo->list.gpuva)) {
> > > > + list_del_init(&vm_bo->list.entry.gem);
> > > > + list_del_init(&vm_bo->list.entry.evict);
> > > > + }
> > > > + drm_gpuva_gem_put(vm_bo);
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_unlink);
> > > > @@ -977,6 +1579,26 @@ drm_gpuva_map(struct drm_gpuva_manager *mgr,
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_map);
> > > > +/**
> > > > + * drm_gpuva_map_get() - helper to insert a &drm_gpuva according to a
> > > > + * &drm_gpuva_op_map
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + * @va: the &drm_gpuva to insert
> > > > + * @op: the &drm_gpuva_op_map to initialize @va with
> > > > + *
> > > > + * Initializes the @va from the @op and inserts it into the given @mgr and
> > > > + * increases the reference count of the corresponding extobj.
> > > > + */
> > > > +void
> > > > +drm_gpuva_map_get(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gpuva *va,
> > > > + struct drm_gpuva_op_map *op)
> > > > +{
> > > > + drm_gpuva_map(mgr, va, op);
> > > > + drm_gpuva_extobj_get(mgr, va->gem.obj);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_map_get);
> > > > +
> > > > /**
> > > > * drm_gpuva_remap() - helper to remap a &drm_gpuva according to a
> > > > * &drm_gpuva_op_remap
> > > > @@ -992,10 +1614,10 @@ drm_gpuva_remap(struct drm_gpuva *prev,
> > > > struct drm_gpuva *next,
> > > > struct drm_gpuva_op_remap *op)
> > > > {
> > > > - struct drm_gpuva *curr = op->unmap->va;
> > > > - struct drm_gpuva_manager *mgr = curr->mgr;
> > > > + struct drm_gpuva *va = op->unmap->va;
> > > > + struct drm_gpuva_manager *mgr = va->mgr;
> > > > - drm_gpuva_remove(curr);
> > > > + drm_gpuva_remove(va);
> > > > if (op->prev) {
> > > > drm_gpuva_init_from_op(prev, op->prev);
> > > > @@ -1009,6 +1631,31 @@ drm_gpuva_remap(struct drm_gpuva *prev,
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_remap);
> > > > +/**
> > > > + * drm_gpuva_remap_get() - helper to remap a &drm_gpuva according to a
> > > > + * &drm_gpuva_op_remap
> > > > + * @prev: the &drm_gpuva to remap when keeping the start of a mapping
> > > > + * @next: the &drm_gpuva to remap when keeping the end of a mapping
> > > > + * @op: the &drm_gpuva_op_remap to initialize @prev and @next with
> > > > + *
> > > > + * Removes the currently mapped &drm_gpuva and remaps it using @prev and/or
> > > > + * @next. Additionally, if the re-map splits the existing &drm_gpuva into two
> > > > + * separate mappings, increases the reference count of the corresponding extobj.
> > > > + */
> > > > +void
> > > > +drm_gpuva_remap_get(struct drm_gpuva *prev,
> > > > + struct drm_gpuva *next,
> > > > + struct drm_gpuva_op_remap *op)
> > > > +{
> > > > + struct drm_gpuva *va = op->unmap->va;
> > > > + struct drm_gpuva_manager *mgr = va->mgr;
> > > > +
> > > > + drm_gpuva_remap(prev, next, op);
> > > > + if (op->prev && op->next)
> > > > + drm_gpuva_extobj_get(mgr, va->gem.obj);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_remap_get);
> > > > +
> > > > /**
> > > > * drm_gpuva_unmap() - helper to remove a &drm_gpuva according to a
> > > > * &drm_gpuva_op_unmap
> > > > @@ -1023,6 +1670,24 @@ drm_gpuva_unmap(struct drm_gpuva_op_unmap *op)
> > > > }
> > > > EXPORT_SYMBOL_GPL(drm_gpuva_unmap);
> > > > +/**
> > > > + * drm_gpuva_unmap_put() - helper to remove a &drm_gpuva according to a
> > > > + * &drm_gpuva_op_unmap
> > > > + * @op: the &drm_gpuva_op_unmap specifying the &drm_gpuva to remove
> > > > + *
> > > > + * Removes the &drm_gpuva associated with the &drm_gpuva_op_unmap and decreases
> > > > + * the reference count of the corresponding extobj.
> > > > + */
> > > > +void
> > > > +drm_gpuva_unmap_put(struct drm_gpuva_op_unmap *op)
> > > > +{
> > > > + struct drm_gpuva *va = op->va;
> > > > +
> > > > + drm_gpuva_unmap(op);
> > > > + drm_gpuva_extobj_put(va->mgr, va->gem.obj);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(drm_gpuva_unmap_put);
> > > > +
> > > > static int
> > > > op_map_cb(const struct drm_gpuva_fn_ops *fn, void *priv,
> > > > u64 addr, u64 range,
> > > > @@ -1663,6 +2328,7 @@ drm_gpuva_gem_unmap_ops_create(struct drm_gpuva_manager *mgr,
> > > > {
> > > > struct drm_gpuva_ops *ops;
> > > > struct drm_gpuva_op *op;
> > > > + struct drm_gpuva_gem *vm_bo;
> > > > struct drm_gpuva *va;
> > > > int ret;
> > > > @@ -1674,7 +2340,7 @@ drm_gpuva_gem_unmap_ops_create(struct drm_gpuva_manager *mgr,
> > > > INIT_LIST_HEAD(&ops->list);
> > > > - drm_gem_for_each_gpuva(va, obj) {
> > > > + drm_gem_for_each_gpuva(va, vm_bo, mgr, obj) {
> > > > op = gpuva_op_alloc(mgr);
> > > > if (!op) {
> > > > ret = -ENOMEM;
> > > > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> > > > index bc9f6aa2f3fe..783ed3ab440d 100644
> > > > --- a/include/drm/drm_gem.h
> > > > +++ b/include/drm/drm_gem.h
> > > > @@ -571,7 +571,7 @@ int drm_gem_evict(struct drm_gem_object *obj);
> > > > * drm_gem_gpuva_init() - initialize the gpuva list of a GEM object
> > > > * @obj: the &drm_gem_object
> > > > *
> > > > - * This initializes the &drm_gem_object's &drm_gpuva list.
> > > > + * This initializes the &drm_gem_object's &drm_gpuva_gem list.
> > > > *
> > > > * Calling this function is only necessary for drivers intending to support the
> > > > * &drm_driver_feature DRIVER_GEM_GPUVA.
> > > > @@ -584,28 +584,44 @@ static inline void drm_gem_gpuva_init(struct drm_gem_object *obj)
> > > > }
> > > > /**
> > > > - * drm_gem_for_each_gpuva() - iternator to walk over a list of gpuvas
> > > > - * @entry__: &drm_gpuva structure to assign to in each iteration step
> > > > - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are associated with
> > > > + * drm_gem_for_each_gpuva_gem() - iterator to walk over a list of &drm_gpuva_gem
> > > > + * @entry__: &drm_gpuva_gem structure to assign to in each iteration step
> > > > + * @obj__: the &drm_gem_object the &drm_gpuva_gem to walk are associated with
> > > > *
> > > > - * This iterator walks over all &drm_gpuva structures associated with the
> > > > - * &drm_gpuva_manager.
> > > > + * This iterator walks over all &drm_gpuva_gem structures associated with the
> > > > + * &drm_gem_object.
> > > > */
> > > > -#define drm_gem_for_each_gpuva(entry__, obj__) \
> > > > - list_for_each_entry(entry__, &(obj__)->gpuva.list, gem.entry)
> > > > +#define drm_gem_for_each_gpuva_gem(entry__, obj__) \
> > > > + list_for_each_entry(entry__, &(obj__)->gpuva.list, list.entry.gem)
> > > > /**
> > > > - * drm_gem_for_each_gpuva_safe() - iternator to safely walk over a list of
> > > > - * gpuvas
> > > > - * @entry__: &drm_gpuva structure to assign to in each iteration step
> > > > - * @next__: &next &drm_gpuva to store the next step
> > > > - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are associated with
> > > > + * drm_gem_for_each_gpuva_gem_safe() - iterator to safely walk over a list of
> > > > + * &drm_gpuva_gem
> > > > + * @entry__: &drm_gpuva_gemstructure to assign to in each iteration step
> > > > + * @next__: &next &drm_gpuva_gem to store the next step
> > > > + * @obj__: the &drm_gem_object the &drm_gpuva_gem to walk are associated with
> > > > *
> > > > - * This iterator walks over all &drm_gpuva structures associated with the
> > > > + * This iterator walks over all &drm_gpuva_gem structures associated with the
> > > > * &drm_gem_object. It is implemented with list_for_each_entry_safe(), hence
> > > > * it is save against removal of elements.
> > > > */
> > > > -#define drm_gem_for_each_gpuva_safe(entry__, next__, obj__) \
> > > > - list_for_each_entry_safe(entry__, next__, &(obj__)->gpuva.list, gem.entry)
> > > > +#define drm_gem_for_each_gpuva_gem_safe(entry__, next__, obj__) \
> > > > + list_for_each_entry_safe(entry__, next__, &(obj__)->gpuva.list, list.entry.gem)
> > > > +
> > > > +/**
> > > > + * drm_gem_for_each_gpuva() - iterator to walk over a list of &drm_gpuva
> > > > + * @va__: &drm_gpuva structure to assign to in each iteration step
> > > > + * @vm_bo__: the &drm_gpuva_gem representing the @mgr__ and @obj__ combination
> > > > + * @mgr__: the &drm_gpuva_manager the &drm_gpuvas to walk are associated with
> > > > + * @obj__: the &drm_gem_object the &drm_gpuvas to walk are associated with
> > > > + *
> > > > + * This iterator walks over all &drm_gpuva structures associated with the
> > > > + * &drm_gpuva_manager and &drm_gem_object.
> > > > + */
> > > > +#define drm_gem_for_each_gpuva(va__, vm_bo__, mgr__, obj__) \
> > > > + for (vm_bo__ = drm_gpuva_gem_find(mgr__, obj__), \
> > > > + va__ = vm_bo__ ? list_first_entry(&vm_bo__->list.gpuva, typeof(*va__), gem.entry) : NULL; \
> > > > + va__ && !list_entry_is_head(va__, &vm_bo__->list.gpuva, gem.entry); \
> > > > + va__ = list_next_entry(va__, gem.entry))
> > > > #endif /* __DRM_GEM_H__ */
> > > > diff --git a/include/drm/drm_gpuva_mgr.h b/include/drm/drm_gpuva_mgr.h
> > > > index ed8d50200cc3..693e2da3f425 100644
> > > > --- a/include/drm/drm_gpuva_mgr.h
> > > > +++ b/include/drm/drm_gpuva_mgr.h
> > > > @@ -26,12 +26,16 @@
> > > > */
> > > > #include <linux/list.h>
> > > > +#include <linux/dma-resv.h>
> > > > +#include <linux/maple_tree.h>
> > > > #include <linux/rbtree.h>
> > > > #include <linux/types.h>
> > > > #include <drm/drm_gem.h>
> > > > +#include <drm/drm_exec.h>
> > > > struct drm_gpuva_manager;
> > > > +struct drm_gpuva_gem;
> > > > struct drm_gpuva_fn_ops;
> > > > /**
> > > > @@ -140,7 +144,7 @@ struct drm_gpuva {
> > > > int drm_gpuva_insert(struct drm_gpuva_manager *mgr, struct drm_gpuva *va);
> > > > void drm_gpuva_remove(struct drm_gpuva *va);
> > > > -void drm_gpuva_link(struct drm_gpuva *va);
> > > > +void drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuva_gem *vm_bo);
> > > > void drm_gpuva_unlink(struct drm_gpuva *va);
> > > > struct drm_gpuva *drm_gpuva_find(struct drm_gpuva_manager *mgr,
> > > > @@ -240,15 +244,137 @@ struct drm_gpuva_manager {
> > > > * @ops: &drm_gpuva_fn_ops providing the split/merge steps to drivers
> > > > */
> > > > const struct drm_gpuva_fn_ops *ops;
> > > > +
> > > > + /**
> > > > + * @d_obj: Dummy GEM object; used internally to pass the GPU VMs
> > > > + * dma-resv to &drm_exec.
> > > > + */
> > > > + struct drm_gem_object d_obj;
> > > > +
> > > > + /**
> > > > + * @resv: the &dma_resv for &drm_gem_objects mapped in this GPU VA
> > > > + * space
> > > > + */
> > > > + struct dma_resv *resv;
> > > > +
> > > > + /**
> > > > + * @exec: the &drm_exec helper to lock external &drm_gem_objects
> > > > + */
> > > > + struct drm_exec exec;
> > > > +
> > > > + /**
> > > > + * @mt_ext: &maple_tree storing external &drm_gem_objects
> > > > + */
> > > > + struct maple_tree mt_ext;
> > > Why are you using a maple tree here? Insertion and removal is O(log(n))
> > > instead of O(1) for a list?
> > >
> > Having a list of drm_gem_objects directly wouldn't work, as multiple GPU-VMs
> > could have mappings of the same extobj.
> >
> > I considered using the VM_BO abstraction (struct drm_gpuva_gem) as list entry
> > instead, which also seems to be the obvious choice. However, there is a locking
> > conflict.
> >
> > A drm_gem_object keeps a list of drm_gpuva_gems, while each drm_gpuva_gem keeps
> > a list of drm_gpuvas. Both lists are either protected with the dma-resv lock of
> > the corresponding drm_gem_object, or with an external lock provided by the
> > driver (see drm_gem_gpuva_set_lock()). The latter is used by drivers performing
> > changes on the GPUVA space directly from the fence signalling path.
> >
> > Now, similar to what drm_gpuva_link() and drm_gpuva_unlink() are doing already,
> > we'd want to add a drm_gpuva_gem to the extobj list for the first mapping being
> > linked and we'd want to remove it for the last one being unlinked.
> >
> > (Actually we'd want to add the drm_gpuva_gem object to the extobj list even
> > before, because otherwise we'd not acquire it's dma-resv lock of this GEM object
> > through drm_gpuva_manager_lock(). But that's trival, we could do that when we
> > create the drm_gpuva_gem, which we need to do anyways.)
> >
> > Anyway, we'd probably want to keep removing the drm_gpuva_gem from the extobj
> > list from drm_gpuva_unlink() when the last mapping of this BO is unlinked. In
> > order to do so, we'd (as discussed above) either need to hold the outer GPU-VM
> > lock or the GPU-VMs dma-resv lock. Both would be illegal in the case
> > drm_gpuva_unlink() is called from within the fence signalling path. For drivers
> > like XE or Nouveau, we'd at least need to make sure to not mess up the locking
> > hierarchy of GPU-VM lock and dma-resv lock of the corresponding BO.
> >
> > Considering all that, I thought it's probably better to track extobjs separate
> > from the drm_gpuva_gem, hence the maple tree choice.
>
> Hm. OK, in Xe we're having a list of the xe_vmas (drm_gpuvas) that point to
> external objects, or in the case of multiple mappings to the same gem
> object, only one of the drm_gpuvas is in the list. These are protected by
> the GPU-VM lock. I don't see a problem with removing those from the fence
> signalling path, though?
I intentionally tried to avoid keeping a list of drm_gpuvas to track extobjs,
since this is generic code I don't know how much mappings of an external object
the corresponding driver potentially creates. This could become a pretty large
list to iterate. Another reason was, that I want to keep the drm_gpuva structure
as small as possible, hence avoiding another list_head.
Now, it sounds like in XE you're doing some kind of optimization just keeping a
single mapping of an extobj in the list? How do you know when to remove it? What
if the mapping from the extobj list gets unmapped, but there is still another
one left in the GPU-VM being backed by the same BO?
>
> Although assuming that's a no-go for GPUVA wouldn't an XArray be a better
> choice, keeping O(1)?
When tracking extobjs, the address of the drm_gem_object is the key while the
reference count is the value. I was thinking of an XArray as well, but I was
worried that the corresponding indices could be too much distributed for an
XArray to still be efficient. Now that I think about it, it's probably not that
bad.
Btw., while I agree trying to make things as efficient as possible, what is the
magnitue for extobjs to be tracked, do we need to worry about the O(log(n))?
>
> >
> > > > +
> > > > + /**
> > > > + * @evict: structure holding the evict list and evict list lock
> > > > + */
> > > > + struct {
> > > > + /**
> > > > + * @list: &list_head storing &drm_gem_objects currently being
> > > > + * evicted
> > > > + */
> > > > + struct list_head list;
> > > > +
> > > > + /**
> > > > + * @lock: spinlock to protect the evict list against concurrent
> > > > + * insertion / removal of different &drm_gpuva_gems
> > > > + */
> > > > + spinlock_t lock;
> > > > + } evict;
> > > > };
> > > > void drm_gpuva_manager_init(struct drm_gpuva_manager *mgr,
> > > > + struct drm_device *drm,
> > > > const char *name,
> > > > u64 start_offset, u64 range,
> > > > u64 reserve_offset, u64 reserve_range,
> > > > const struct drm_gpuva_fn_ops *ops);
> > > > void drm_gpuva_manager_destroy(struct drm_gpuva_manager *mgr);
> > > > +/**
> > > > + * DRM_GPUVA_EXEC - returns the &drm_gpuva_managers &drm_exec instance
> > > > + * @mgr: the &drm_gpuva_managers to return the &drm_exec instance for
> > > > + */
> > > > +#define DRM_GPUVA_EXEC(mgr) &(mgr)->exec
> > > A struct ww_acquire_ctx and thus a drm_exec is fundamentally per task and
> > > should typically be allocated on the stack. Otherwise you'd need to protect
> > > the mgr->exec member with an exclusive lock throughout the locking process,
> > > and that's not what we want.
> > Oh, good point. I think it works in Nouveau, because there it's implicitly
> > protected with the job submission lock.
> >
> > > Did you consider subclassing a drm_exec for drm_gpuva purposes and add
> > > needed ops to it: Like so:
> > That's a good idea, will take this into V2.
>
> Actually, I'm not fully sure that was a good idea: I've now have a working
> version of Xe ported over to drm_exec, having these helpers in mind and with
> the intention to start using them as they mature. What I found, though is
> that open-coding the drm_exec loop is not all that bad, but that building
> blocks that can be called from within the loop are useful:
>
> Like the drm_gpuva_prepare_objects() and an imaginary
> drm_gpuva_prepare_gpuva() that locks the vm resv and the resv of the object
> (if different and the gpuva points to the object. And
> drm_gpuva_prepare_array() although we don't use it within Xe. That means you
> can use these building blocks like helpers and avoid the fn() callback by
> instead open-coding.
>
> But I guess YMMV.
That's exactly why those building blocks are exported, I already had in mind
that there might be drivers which still want to open-code the drm_exec loop,
while others might just want a simple interface to lock everything.
I still think it is a good idea, but I'd keep that as simple as possible. And
for everything else just let the driver open-code it and use the "building
blocks" - will also expand the bulding blocks to what you mentioned above.
>
> >
> > > struct drm_gpuva_exec_ops {
> > > int (*fn) (struct drm_gpuva_exec *exec, int num_fences);
> > Is this the fn argument from drm_gpuva_manager_lock_extra()?
> >
> > > int (*bo_validate) (struct drm_gpuva_exec *exec, struct drm_gem_object
> > > *obj);
> > I guess we could also keep that within the drm_gpuva_fn_ops? This should always
> > be the same callback, right?
> >
> > > };
> > >
> > > struct drm_gpuva_exec {
> > > const struct drm_gpuva_exec_ops *ops;
> > > struct drm_exec exec;
> > > struct drm_gpuva_manager *mgr;
> > > };
> > >
> > > Although I'd actually expect bo_validate to be part of fn in the typical
> > > case. The drm_gpuva_exec would then be allocated by the caller on the stack.
> > This doesn't sound like my assumption about fn() above is correct.
>
> Well one important thing in our conversion is that ttm_bo_validate () needs
> to be in the until_all_locked() loop. We want to be able soon to use
> sleeping locks for eviction, so a xe_bo_validate() would, at least
> temporarily, add locked objects to the drm_exec list of locked objects. That
> means everything that may end up calling validate deep within the call chain
> needs to be part of the until_all_locked() loop, so our
> drm_gpuva_manager_lock_extra() fn callback would include those validates and
> look different all the time. Hence that's why open-coding isn't all that
> bad...
Oh, I see. You indeed want to call validate() from within until_all_locked().
>
> /Thomas
>
>
> >
> > >
> > > > +
> > > > +int drm_gpuva_manager_lock_extra(struct drm_gpuva_manager *mgr,
> > > > + int (*fn)(struct drm_gpuva_manager *mgr,
> > > > + void *priv, unsigned int num_fences),
> > > > + void *priv,
> > > > + unsigned int num_fences,
> > > > + bool interruptible);
> > > > +
> > > > +int drm_gpuva_manager_lock_array(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object **objs,
> > > > + unsigned int num_objs,
> > > > + unsigned int num_fences,
> > > > + bool interruptible);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_lock() - lock all dma-resv of all assoiciated BOs
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + * @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_gpuva_manager contains mappings of.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +static inline int
> > > > +drm_gpuva_manager_lock(struct drm_gpuva_manager *mgr,
> > > > + unsigned int num_fences,
> > > > + bool interruptible)
> > > > +{
> > > > + return drm_gpuva_manager_lock_extra(mgr, NULL, NULL, num_fences,
> > > > + interruptible);
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_manager_lock() - lock all dma-resv of all assoiciated BOs
> > > > + * @mgr: the &drm_gpuva_manager
> > > > + *
> > > > + * Releases all dma-resv locks of all &drm_gem_objects previously acquired
> > > > + * through drm_gpuva_manager_lock() or its variants.
> > > > + *
> > > > + * Returns: 0 on success, negative error code on failure.
> > > > + */
> > > > +static inline void
> > > > +drm_gpuva_manager_unlock(struct drm_gpuva_manager *mgr)
> > > > +{
> > > > + drm_exec_fini(&mgr->exec);
> > > > +}
> > > > +
> > > > +int drm_gpuva_manager_validate(struct drm_gpuva_manager *mgr);
> > > > +void drm_gpuva_manager_resv_add_fence(struct drm_gpuva_manager *mgr,
> > > > + struct dma_fence *fence,
> > > > + enum dma_resv_usage private_usage,
> > > > + enum dma_resv_usage extobj_usage);
> > > > +
> > > > +int drm_gpuva_extobj_insert(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +void drm_gpuva_extobj_get(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +void drm_gpuva_extobj_put(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_is_extobj() - indicates whether the given &drm_gem_object is an
> > > > + * external object
> > > > + * @mgr: the &drm_gpuva_manager to check
> > > > + * @obj: the &drm_gem_object to check
> > > > + *
> > > > + * Returns: true if the &drm_gem_object &dma_resv differs from the
> > > > + * &drm_gpuva_managers &dma_resv, false otherwise
> > > > + */
> > > > +static inline bool drm_gpuva_is_extobj(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj)
> > > > +{
> > > > + return obj && obj->resv != mgr->resv;
> > > > +}
> > > > +
> > > > static inline struct drm_gpuva *
> > > > __drm_gpuva_next(struct drm_gpuva *va)
> > > > {
> > > > @@ -327,6 +453,138 @@ __drm_gpuva_next(struct drm_gpuva *va)
> > > > #define drm_gpuva_for_each_va_safe(va__, next__, mgr__) \
> > > > list_for_each_entry_safe(va__, next__, &(mgr__)->rb.list, rb.entry)
> > > > +/**
> > > > + * struct drm_gpuva_gem - structure representing a &drm_gpuva_manager and
> > > > + * &drm_gem_object combination
> > > > + *
> > > > + * This structure is an abstraction representing a &drm_gpuva_manager and
> > > > + * &drm_gem_object combination. It serves as an indirection to accelerate
> > > > + * iterating all &drm_gpuvas within a &drm_gpuva_manager backed by the same
> > > > + * &drm_gem_object.
> > > > + *
> > > > + * Furthermore it is used cache evicted GEM objects for a certain GPU-VM to
> > > > + * accelerate validation.
> > > > + *
> > > > + * Typically, drivers want to create an instance of a struct drm_gpuva_gem once
> > > > + * a GEM object is mapped first in a GPU-VM and release the instance once the
> > > > + * last mapping of the GEM object in this GPU-VM is unmapped.
> > > > + */
> > > > +struct drm_gpuva_gem {
> > > > +
> > > > + /**
> > > > + * @mgr: The &drm_gpuva_manager the @obj is mapped in.
> > > > + */
> > > > + struct drm_gpuva_manager *mgr;
> > > > +
> > > > + /**
> > > > + * @obj: The &drm_gem_object being mapped in the @mgr.
> > > > + */
> > > > + struct drm_gem_object *obj;
> > > > +
> > > > + /**
> > > > + * @kref: The reference count for this &drm_gpuva_gem.
> > > > + */
> > > > + struct kref kref;
> > > > +
> > > > + /**
> > > > + * @list: Structure containing all &list_heads.
> > > > + */
> > > > + struct {
> > > > + /**
> > > > + * @gpuva: The list of linked &drm_gpuvas.
> > > > + */
> > > > + struct list_head gpuva;
> > > > +
> > > > + /**
> > > > + * @entry: Structure containing all &list_heads serving as
> > > > + * entry.
> > > > + */
> > > > + struct {
> > > > + /**
> > > > + * @gem: List entry to attach to the &drm_gem_objects
> > > > + * gpuva list.
> > > > + */
> > > > + struct list_head gem;
> > > > +
> > > > + /**
> > > > + * @evict: List entry to attach to the
> > > > + * &drm_gpuva_managers evict list.
> > > > + */
> > > > + struct list_head evict;
> > > > + } entry;
> > > > + } list;
> > > > +};
> > > > +
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_obtain(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_obtain_prealloc(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj,
> > > > + struct drm_gpuva_gem *__vm_bo);
> > > > +
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_find(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +
> > > > +void drm_gpuva_gem_evict(struct drm_gem_object *obj, bool evict);
> > > > +
> > > > +struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_create(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gem_object *obj);
> > > > +void drm_gpuva_gem_destroy(struct kref *kref);
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_get() - acquire a struct drm_gpuva_gem reference
> > > > + * @vm_bo: the &drm_gpuva_gem to acquire the reference of
> > > > + *
> > > > + * This function acquires an additional reference to @vm_bo. It is illegal to
> > > > + * call this without already holding a reference. No locks required.
> > > > + */
> > > > +static inline struct drm_gpuva_gem *
> > > > +drm_gpuva_gem_get(struct drm_gpuva_gem *vm_bo)
> > > > +{
> > > > + kref_get(&vm_bo->kref);
> > > > + return vm_bo;
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_put() - drop a struct drm_gpuva_gem reference
> > > > + * @vm_bo: the &drm_gpuva_gem to release the reference of
> > > > + *
> > > > + * This releases a reference to @vm_bo.
> > > > + */
> > > > +static inline void
> > > > +drm_gpuva_gem_put(struct drm_gpuva_gem *vm_bo)
> > > > +{
> > > > + kref_put(&vm_bo->kref, drm_gpuva_gem_destroy);
> > > > +}
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_for_each_va() - iterator to walk over a list of &drm_gpuva
> > > > + * @va__: &drm_gpuva structure to assign to in each iteration step
> > > > + * @vm_bo__: the &drm_gpuva_gem the &drm_gpuva to walk are associated with
> > > > + *
> > > > + * This iterator walks over all &drm_gpuva structures associated with the
> > > > + * &drm_gpuva_gem.
> > > > + */
> > > > +#define drm_gpuva_gem_for_each_va(va__, vm_bo__) \
> > > > + list_for_each_entry(va__, &(vm_bo)->list.gpuva, gem.entry)
> > > > +
> > > > +/**
> > > > + * drm_gpuva_gem_for_each_va_safe() - iterator to safely walk over a list of
> > > > + * &drm_gpuva
> > > > + * @va__: &drm_gpuva structure to assign to in each iteration step
> > > > + * @next__: &next &drm_gpuva to store the next step
> > > > + * @vm_bo__: the &drm_gpuva_gem the &drm_gpuva to walk are associated with
> > > > + *
> > > > + * This iterator walks over all &drm_gpuva structures associated with the
> > > > + * &drm_gpuva_gem. It is implemented with list_for_each_entry_safe(), hence
> > > > + * it is save against removal of elements.
> > > > + */
> > > > +#define drm_gpuva_gem_for_each_va_safe(va__, next__, vm_bo__) \
> > > > + list_for_each_entry_safe(va__, next__, &(vm_bo)->list.gpuva, gem.entry)
> > > > +
> > > > /**
> > > > * enum drm_gpuva_op_type - GPU VA operation type
> > > > *
> > > > @@ -641,6 +899,30 @@ struct drm_gpuva_fn_ops {
> > > > */
> > > > void (*op_free)(struct drm_gpuva_op *op);
> > > > + /**
> > > > + * @vm_bo_alloc: called when the &drm_gpuva_manager allocates
> > > > + * a struct drm_gpuva_gem
> > > > + *
> > > > + * Some drivers may want to embed struct drm_gpuva_gem into driver
> > > > + * specific structures. By implementing this callback drivers can
> > > > + * allocate memory accordingly.
> > > > + *
> > > > + * This callback is optional.
> > > > + */
> > > > + struct drm_gpuva_gem *(*vm_bo_alloc)(void);
> > > > +
> > > > + /**
> > > > + * @vm_bo_free: called when the &drm_gpuva_manager frees a
> > > > + * struct drm_gpuva_gem
> > > > + *
> > > > + * Some drivers may want to embed struct drm_gpuva_gem into driver
> > > > + * specific structures. By implementing this callback drivers can
> > > > + * free the previously allocated memory accordingly.
> > > > + *
> > > > + * This callback is optional.
> > > > + */
> > > > + void (*vm_bo_free)(struct drm_gpuva_gem *vm_bo);
> > > > +
> > > > /**
> > > > * @sm_step_map: called from &drm_gpuva_sm_map to finally insert the
> > > > * mapping once all previous steps were completed
> > > > @@ -684,6 +966,17 @@ struct drm_gpuva_fn_ops {
> > > > * used.
> > > > */
> > > > int (*sm_step_unmap)(struct drm_gpuva_op *op, void *priv);
> > > > +
> > > > + /**
> > > > + * @bo_validate: called from drm_gpuva_manager_validate()
> > > > + *
> > > > + * Drivers receive this callback for every evicted &drm_gem_object being
> > > > + * mapped in the corresponding &drm_gpuva_manager.
> > > > + *
> > > > + * 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_gpuva_sm_map(struct drm_gpuva_manager *mgr, void *priv,
> > > > @@ -696,11 +989,18 @@ int drm_gpuva_sm_unmap(struct drm_gpuva_manager *mgr, void *priv,
> > > > void drm_gpuva_map(struct drm_gpuva_manager *mgr,
> > > > struct drm_gpuva *va,
> > > > struct drm_gpuva_op_map *op);
> > > > +void drm_gpuva_map_get(struct drm_gpuva_manager *mgr,
> > > > + struct drm_gpuva *va,
> > > > + struct drm_gpuva_op_map *op);
> > > > void drm_gpuva_remap(struct drm_gpuva *prev,
> > > > struct drm_gpuva *next,
> > > > struct drm_gpuva_op_remap *op);
> > > > +void drm_gpuva_remap_get(struct drm_gpuva *prev,
> > > > + struct drm_gpuva *next,
> > > > + struct drm_gpuva_op_remap *op);
> > > > void drm_gpuva_unmap(struct drm_gpuva_op_unmap *op);
> > > > +void drm_gpuva_unmap_put(struct drm_gpuva_op_unmap *op);
> > > > #endif /* __DRM_GPUVA_MGR_H__ */
>