Message-ID: <d7a46efbf5fdcc62a96fb09579ff72c70e64d5fb.camel@linux.intel.com>
Date:   Tue, 31 Oct 2023 12:34:38 +0100
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 v7 5/7] drm/gpuvm: track/lock/validate
 external/evicted objects

On Mon, 2023-10-23 at 22:16 +0200, 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>

The checkpatch.pl warning still persists:
WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
#627: FILE: drivers/gpu/drm/drm_gpuvm.c:1347:
+		return -ENOTSUPP;

> ---
>  drivers/gpu/drm/drm_gpuvm.c | 633
> ++++++++++++++++++++++++++++++++++++
>  include/drm/drm_gpuvm.h     | 250 ++++++++++++++
>  2 files changed, 883 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gpuvm.c
> b/drivers/gpu/drm/drm_gpuvm.c
> index 7f4f5919f84c..01cbeb98755a 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
> + * lists 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 +670,201 @@
>   *     }
>   */
>  
> +/**
> + * get_next_vm_bo_from_list() - get the next vm_bo element
> + * @__gpuvm: the &drm_gpuvm
> + * @__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
> get_next_vm_bo_from_list()
> + *
> + * 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                                                 
>                    \
> +                       drm_WARN_ON((__gpuvm)-
> >drm,                                     \
> +                                   (__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
> + * @__gpuvm: the &drm_gpuvm
> + * @__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
> + * @__vm_bo: the struct drm_gpuvm_bo to assign in each iteration
> step
> + *
> + * 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;
> + *     }
> + *     // Drop ref in case we break out of the loop.
> + *     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 &drm_gpuvm
> + * @__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)
> @@ -763,6 +987,12 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const
> char *name,
>         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);
> +
>         gpuvm->name = name ? name : "unknown";
>         gpuvm->flags = flags;
>         gpuvm->ops = ops;
> @@ -805,10 +1035,352 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
>         drm_WARN(gpuvm->drm, !RB_EMPTY_ROOT(&gpuvm->rb.tree.rb_root),
>                  "GPUVA tree is not empty, potentially leaking
> memory.\n");
>  
> +       drm_WARN(gpuvm->drm, !list_empty(&gpuvm->extobj.list),
> +                "Extobj list should be empty.\n");
> +       drm_WARN(gpuvm->drm, !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);
> +       }
> +
> +       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.

s/Returns:/Return:/g

Otherwise LGTM.

/Thomas

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