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Date:   Fri, 13 Oct 2023 14:04:27 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.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 10/10/23 08:26, Thomas Hellström wrote:
> 
> On 10/9/23 16:45, Danilo Krummrich wrote:
>> On 10/9/23 15:36, Thomas Hellström wrote:
>>>
>>> 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?
>>
>> Why? It's still evicted, hence why not indicate it? It could be useful for a
>> validate_range() use case.
> 
> I guess that boils down to what vm_bo->evicted is supposed to mean. I have been using it as "This bo needs to be put on the evicted list", but if we instead mean "This bo was once evicted and might need revalidation and needs rebinding to this VM" then it's OK not to clear it, I guess. But note that another VM might have already re-validated the gem BO, and also if the locking loop or validate loop restarts due to -EINTR or -EDEADLK, then the drm_gpuvm_bo_list_add() will be called multiple times, which is OK but unnecessary. So I'd vote for "This bo needs to be put on the eviced list".

In case of a drm_exec loop restart, the additional drm_gpuvm_bo_list_add() is rather negligible. As mentioned, keeping drm_gpuvm_bo::evicted in an up to date state could be a useful addition to drivers. Besides that, I'd rather make this field safe to use by drivers than document that it's *not* safe to look up for drivers and should only be used with care internally.

> 
>>
>>>
>>>
>>>> +    }
>>>> +
>>>> +    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?
>>
>> It doesn't need it by itself, but since we have drm_gpuvm_bo::evicted now, I want it to
>> consistently indicate whether the BO is evicted or not.
> 
> OK, I guess that ties to the meaning of bo->evicted, as discussed above.
> 
>>
>>>> +
>>>> +        if (!lock)
>>>> +            return;
>>>
>>> Here the !lock case can not remove the gpuvm_bo from the list?
>>
>> You mean because we'd expect that drm_gpuvm_bo_evict(vm_bo, false) can only be called from
>> within gpuvm_validate(), which requires the VM's resv lock? What if there is a ttm_validate()
>> call for only this GEM obj?
>>
>> My idea was to remove VM_BOs from the evicted list in gpuvm_validate() directly, but I'm afraid
>> I forgot that.
> 
> Yes, I think the helper could do it if validate() is successful. But what I meant above was that if the *driver* is responsible for removing object from the evicted list, then if it's a RESV_PROTECTED vm, it can't do that because drm_gpuvm_bo_evict(gpuvm, false) will never get to removing it from the list because it returns early.

Well, with a RESV_PROTECTED VM we can't expect the evicted list to be up to date until we called drm_gpuvm_prepare_objects() by definition. In drm_gpuvm_prepare_objects() we'd need to

if (vm_bo->evicted)
   add_to_list()
else
   remove_from_list()

though, because a driver could lock and unlock those objects without validation.

> 
> Thanks,
> 
> Thomas
> 
> 
>>
>>>
>>> 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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