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Message-ID: <6b16ab6f-b1a2-efdb-04bf-5af4c3de381b@linux.intel.com>
Date:   Tue, 3 Oct 2023 11:11:10 +0200
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Subject: Re: [PATCH drm-misc-next v5 4/6] drm/gpuvm: track/lock/validate
 external/evicted objects
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From:   =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= 
        <thomas.hellstrom@linux.intel.com>
To:     Danilo Krummrich <dakr@redhat.com>, airlied@gmail.com,
        daniel@ffwll.ch, matthew.brost@intel.com, sarah.walker@imgtec.com,
        donald.robson@imgtec.com, boris.brezillon@collabora.com,
        christian.koenig@amd.com, faith@gfxstrand.net
Cc:     dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20230928191624.13703-1-dakr@redhat.com>
 <20230928191624.13703-5-dakr@redhat.com>
 <e4e68970-c7c9-55e2-9483-01252f38c956@linux.intel.com>
In-Reply-To: <e4e68970-c7c9-55e2-9483-01252f38c956@linux.intel.com>
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Hi Again,


On 10/3/23 10:36, Thomas Hellström wrote:
> Hi, Danilo,
>
> On 9/28/23 21:16, 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@intel.com>
>> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
>> ---
>>   drivers/gpu/drm/drm_gpuvm.c | 642 ++++++++++++++++++++++++++++++++++++
>>   include/drm/drm_gpuvm.h     | 240 ++++++++++++++
>>   2 files changed, 882 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
>> index 27100423154b..770bb3d68d1f 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);                \
>
> Here we unconditionally take the spinlocks while iterating, and the 
> main point of DRM_GPUVM_RESV_PROTECTED was really to avoid that?


Never mind, I missed this code wasn't used in the RESV_PROTECTED case.

>
>
>> +        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)) {
> And unnecessarily grab a reference in the RESV_PROTECTED case.

Same here.


>>             \
>> + 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;                                \
>> +    })
>
> IMHO this lockless list iteration looks very complex and should be 
> pretty difficult to maintain while moving forward, also since it pulls 
> the gpuvm_bos off the list, list iteration needs to be protected by an 
> outer lock anyway. Also from what I understand from Boris, the extobj 
> list would typically not need the fine-grained locking; only the evict 
> list? Also it seems that if we are to maintain two modes here, for 
> reasonably clean code we'd need two separate instances of 
> get_next_bo_from_list().
(And we indeed do, sort of),
>
> For the !RESV_PROTECTED case, perhaps one would want to consider the 
> solution used currently in xe, where the VM maintains two evict lists. 
> One protected by a spinlock and one protected by the VM resv. When the 
> VM resv is locked to begin list traversal, the spinlock is locked 
> *once* and the spinlock-protected list is looped over and copied into 
> the resv protected one. For traversal, the resv protected one is used.
>
> If that works with all concerns raised so far,  list traversal would 
> be greatly simplified, and no need for a separate RESV_PROTECTED mode.

Although this doesn't work with async removal from lists. Not sure if 
that's still a use-case though.

Thanks,

Thomas


>
> Also some inline comments below.
>
>
>> +
>> +/**
>> + * 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 inline 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 inline void
>> +cond_spin_lock(spinlock_t *lock, bool cond)
>> +{
>> +    if (cond)
>> +        spin_lock(lock);
>> +}
>> +
>> +static inline void
>> +cond_spin_unlock(spinlock_t *lock, bool cond)
>> +{
>> +    if (cond)
>> +        spin_unlock(lock);
>> +}
>> +
>> +static inline 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 inline 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 +1026,373 @@ 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;
>> +    }
>> +
>> +    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 abstraction
>> + * @num_fences: the amount of &dma_fences to reserve
>> + * @interruptible: sleep interruptible if waiting
>> + *
>> + * Acquires all dma-resv locks of all &drm_gem_objects the given
>> + * &drm_gpuvm contains mappings of.
>> + *
>> + * Addionally, when calling this function with struct 
>> drm_gpuvm_exec::extra
>> + * being set the driver receives the given @fn callback to lock 
>> additional
>> + * dma-resv in the context of the &drm_gpuvm_exec instance. 
>> Typically, drivers
>> + * would call drm_exec_prepare_obj() from within this callback.
>> + *
>> + * Returns: 0 on success, negative error code on failure.
>> + */
>> +int
>> +drm_gpuvm_exec_lock(struct drm_gpuvm_exec *vm_exec,
>> +            unsigned int num_fences,
>> +            bool interruptible)
>> +{
>> +    struct drm_gpuvm *gpuvm = vm_exec->vm;
>> +    struct drm_exec *exec = &vm_exec->exec;
>> +    uint32_t flags;
>> +    int ret;
>> +
>> +    flags = interruptible ? DRM_EXEC_INTERRUPTIBLE_WAIT : 0 |
>> +        DRM_EXEC_IGNORE_DUPLICATES;
>> +
>> +    drm_exec_init(exec, flags);
>> +
>> +    drm_exec_until_all_locked(exec) {
>> +        ret = drm_gpuvm_prepare_vm(gpuvm, exec, num_fences);
>> +        drm_exec_retry_on_contention(exec);
>> +        if (ret)
>> +            goto err;
>> +
>> +        ret = drm_gpuvm_prepare_objects(gpuvm, exec, num_fences);
>> +        drm_exec_retry_on_contention(exec);
>> +        if (ret)
>> +            goto err;
>> +
>> +        if (vm_exec->extra.fn) {
>> +            ret = vm_exec->extra.fn(vm_exec, num_fences);
>> +            drm_exec_retry_on_contention(exec);
>> +            if (ret)
>> +                goto err;
>> +        }
>> +    }
>> +
>> +    return 0;
>> +
>> +err:
>> +    drm_exec_fini(exec);
>> +    return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock);
>> +
>> +static int
>> +fn_lock_array(struct drm_gpuvm_exec *vm_exec, unsigned int num_fences)
>> +{
>> +    struct {
>> +        struct drm_gem_object **objs;
>> +        unsigned int num_objs;
>> +    } *args = vm_exec->extra.priv;
>> +
>> +    return drm_exec_prepare_array(&vm_exec->exec, args->objs,
>> +                      args->num_objs, num_fences);
>> +}
>> +
>> +/**
>> + * drm_gpuvm_exec_lock_array() - lock all dma-resv of all 
>> assoiciated BOs
>> + * @vm_exec: the &drm_gpuvm_exec abstraction
>> + * @objs: additional &drm_gem_objects to lock
>> + * @num_objs: the number of additional &drm_gem_objects to lock
>> + * @num_fences: the amount of &dma_fences to reserve
>> + * @interruptible: sleep interruptible if waiting
>> + *
>> + * Acquires all dma-resv locks of all &drm_gem_objects the given 
>> &drm_gpuvm
>> + * contains mappings of, plus the ones given through @objs.
>> + *
>> + * Returns: 0 on success, negative error code on failure.
>> + */
>> +int
>> +drm_gpuvm_exec_lock_array(struct drm_gpuvm_exec *vm_exec,
>> +              struct drm_gem_object **objs,
>> +              unsigned int num_objs,
>> +              unsigned int num_fences,
>> +              bool interruptible)
>> +{
>> +    struct {
>> +        struct drm_gem_object **objs;
>> +        unsigned int num_objs;
>> +    } args;
>> +
>> +    args.objs = objs;
>> +    args.num_objs = num_objs;
>> +
>> +    vm_exec->extra.fn = fn_lock_array;
>> +    vm_exec->extra.priv = &args;
>> +
>> +    return drm_gpuvm_exec_lock(vm_exec, num_fences, interruptible);
>> +}
>> +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock_array);
>> +
>> +/**
>> + * drm_gpuvm_exec_lock_range() - prepare all BOs mapped within a 
>> given range
>> + * @vm_exec: the &drm_gpuvm_exec abstraction
>> + * @addr: the start address within the VA space
>> + * @range: the range to iterate within the VA space
>> + * @num_fences: the amount of &dma_fences to reserve
>> + * @interruptible: sleep interruptible if waiting
>> + *
>> + * Acquires all dma-resv locks of all &drm_gem_objects mapped 
>> between @addr and
>> + * @addr + @range.
>> + *
>> + * Returns: 0 on success, negative error code on failure.
>> + */
>> +int
>> +drm_gpuvm_exec_lock_range(struct drm_gpuvm_exec *vm_exec,
>> +              u64 addr, u64 range,
>> +              unsigned int num_fences,
>> +              bool interruptible)
>> +{
>> +    struct drm_gpuvm *gpuvm = vm_exec->vm;
>> +    struct drm_exec *exec = &vm_exec->exec;
>> +    uint32_t flags;
>> +    int ret;
>> +
>> +    flags = interruptible ? DRM_EXEC_INTERRUPTIBLE_WAIT : 0 |
>> +        DRM_EXEC_IGNORE_DUPLICATES;
>> +
>> +    drm_exec_init(exec, flags);
>> +
>> +    drm_exec_until_all_locked(exec) {
>> +        ret = drm_gpuvm_prepare_range(gpuvm, exec, addr, range,
>> +                          num_fences);
>> +        drm_exec_retry_on_contention(exec);
>> +        if (ret)
>> +            goto err;
>> +    }
>> +
>> +    return ret;
>> +
>> +err:
>> +    drm_exec_fini(exec);
>> +    return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(drm_gpuvm_exec_lock_range);
>> +
>> +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;
>> +
>> +#ifdef CONFIG_LOCKDEP
>> +    drm_gpuvm_resv_assert_held(gpuvm);
>> +    list_for_each_entry(vm_bo, &gpuvm->extobj.list, list.entry.extobj)
>> +        dma_resv_assert_held(vm_bo->obj->resv);
>> +#endif
>> +
>> +    /* 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 +1425,9 @@ 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 +1448,9 @@ 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 +1587,55 @@ 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_gem_object *obj = vm_bo->obj;
>> +
>> +    dma_resv_assert_held(obj->resv);
>> +
>> +    /* Always lock list transactions, even if 
>> DRM_GPUVM_RESV_PROTECTED is
>> +     * set. This is required to protect multiple concurrent calls to
>> +     * drm_gpuvm_bo_evict() with BOs with different dma_resv.
>> +     */
>
> This doesn't work. The RESV_PROTECTED case requires the evicted flag 
> we discussed before. The list is either protected by the spinlock or 
> the resv. Otherwise a list add could race with a list removal elsewhere.
>
> Thanks,
>
> Thomas
>
>