Re: [PATCH drm-misc-next v6 1/6] drm/gpuvm: add common dma-resv per struct drm_gpuvm

[Danilo Krummrich <dakr@redhat.com>]

On 10/13/23 13:38, Thomas Hellström wrote:
> On Mon, 2023-10-09 at 01:32 +0200, Danilo Krummrich wrote:
>> Provide a common dma-resv for GEM objects not being used outside of
>> this
>> GPU-VM. This is used in a subsequent patch to generalize dma-resv,
>> external and evicted object handling and GEM validation.
>>
>> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
>> ---
>>   drivers/gpu/drm/drm_gpuvm.c            | 56
>> +++++++++++++++++++++++++-
>>   drivers/gpu/drm/nouveau/nouveau_uvmm.c | 13 +++++-
>>   include/drm/drm_gpuvm.h                | 35 +++++++++++++++-
>>   3 files changed, 99 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gpuvm.c
>> b/drivers/gpu/drm/drm_gpuvm.c
>> index 02ecb45a2544..ebda9d594165 100644
>> --- a/drivers/gpu/drm/drm_gpuvm.c
>> +++ b/drivers/gpu/drm/drm_gpuvm.c
>> @@ -61,6 +61,15 @@
>>    * contained within struct drm_gpuva already. Hence, for inserting
>> &drm_gpuva
>>    * entries from within dma-fence signalling critical sections it is
>> enough to
>>    * pre-allocate the &drm_gpuva structures.
>> + *
>> + * &drm_gem_objects which are private to a single VM can share a
>> common
>> + * &dma_resv in order to improve locking efficiency (e.g. with
>> &drm_exec).
>> + * For this purpose drivers must pass a &drm_gem_object to
>> drm_gpuvm_init(), in
>> + * the following called 'root object', which serves as the container
> 
> Nit: Perhaps resv object altough it might typically be the root page-
> table object, that doesn't have any meaning to drm_gpuvm, which uses it
> solely as a container for the resv?

With "root" I didn't want to refer to the object representing the root
page-table object, but being *the* object every other (internal) object
needs to keep a reference to. Maybe I should be more explicit here and say
that drivers need to make sure every internal object requires a reference
to take a reference to this root object.

> 
>> of the
>> + * GPUVM's shared &dma_resv. This root object can be a driver
>> specific
>> + * &drm_gem_object, such as the &drm_gem_object containing the root
>> page table,
>> + * but it can also be a 'dummy' object, which can be allocated with
>> + * drm_gpuvm_root_object_alloc().
>>    */
>>   
>>   /**
>> @@ -652,9 +661,47 @@ drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm,
>>                 !drm_gpuvm_in_kernel_node(gpuvm, addr, range);
>>   }
>>   
>> +static void
>> +drm_gpuvm_gem_object_free(struct drm_gem_object *obj)
>> +{
>> +       drm_gem_object_release(obj);
>> +       kfree(obj);
>> +}
>> +
>> +static const struct drm_gem_object_funcs drm_gpuvm_object_funcs = {
>> +       .free = drm_gpuvm_gem_object_free,
>> +};
>> +
>> +/**
>> + * drm_gpuvm_root_object_alloc() - allocate a dummy &drm_gem_object
>> + * @drm: the drivers &drm_device
>> + *
>> + * Allocates a dummy &drm_gem_object which can be passed to
>> drm_gpuvm_init() in
>> + * order to serve as root GEM object providing the &drm_resv shared
>> across
>> + * &drm_gem_objects local to a single GPUVM.
>> + *
>> + * Returns: the &drm_gem_object on success, NULL on failure
>> + */
>> +struct drm_gem_object *
>> +drm_gpuvm_root_object_alloc(struct drm_device *drm)
>> +{
>> +       struct drm_gem_object *obj;
>> +
>> +       obj = kzalloc(sizeof(*obj), GFP_KERNEL);
>> +       if (!obj)
>> +               return NULL;
>> +
>> +       obj->funcs = &drm_gpuvm_object_funcs;
>> +       drm_gem_private_object_init(drm, obj, 0);
>> +
>> +       return obj;
>> +}
>> +EXPORT_SYMBOL_GPL(drm_gpuvm_root_object_alloc);
>> +
>>   /**
>>    * drm_gpuvm_init() - initialize a &drm_gpuvm
>>    * @gpuvm: pointer to the &drm_gpuvm to initialize
>> + * @r_obj: the root &drm_gem_object providing the GPUVM's common
>> &dma_resv
>>    * @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
>> @@ -668,7 +715,7 @@ drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm,
>>    * &name is expected to be managed by the surrounding driver
>> structures.
>>    */
>>   void
>> -drm_gpuvm_init(struct drm_gpuvm *gpuvm,
>> +drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_gem_object
>> *r_obj,
>>                 const char *name,
>>                 u64 start_offset, u64 range,
>>                 u64 reserve_offset, u64 reserve_range,
>> @@ -683,6 +730,9 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm,
>>   
>>          gpuvm->name = name ? name : "unknown";
>>          gpuvm->ops = ops;
>> +       gpuvm->r_obj = r_obj;
>> +
>> +       drm_gem_object_get(r_obj);
>>   
>>          memset(&gpuvm->kernel_alloc_node, 0, sizeof(struct
>> drm_gpuva));
>>   
>> @@ -713,7 +763,9 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
>>                  __drm_gpuva_remove(&gpuvm->kernel_alloc_node);
>>   
>>          WARN(!RB_EMPTY_ROOT(&gpuvm->rb.tree.rb_root),
>> -            "GPUVA tree is not empty, potentially leaking memory.");
>> +            "GPUVA tree is not empty, potentially leaking
>> memory.\n");
> 
> Should we cache the drm device in struct drm_gpuvm and use drm_warn()
> here instead of WARN?

I'd guess the additional backtrace of WARN() isn't overly useful in this
case. However, it might be a bit more obvious in dmesg due to its
verboseness. Not a strong opinion on that, though.

> 
>> +
>> +       drm_gem_object_put(gpuvm->r_obj);
>>   }
>>   EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
>>   
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>> b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>> index 5cf892c50f43..4dea847ef989 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
>> @@ -1808,8 +1808,9 @@ int
>>   nouveau_uvmm_init(struct nouveau_uvmm *uvmm, struct nouveau_cli
>> *cli,
>>                    u64 kernel_managed_addr, u64 kernel_managed_size)
>>   {
>> -       int ret;
>> +       struct drm_gem_object *r_obj;
>>          u64 kernel_managed_end = kernel_managed_addr +
>> kernel_managed_size;
>> +       int ret;
>>   
>>          mutex_init(&uvmm->mutex);
>>          dma_resv_init(&uvmm->resv);
>> @@ -1833,14 +1834,22 @@ nouveau_uvmm_init(struct nouveau_uvmm *uvmm,
>> struct nouveau_cli *cli,
>>                  goto out_unlock;
>>          }
>>   
>> +       r_obj = drm_gpuvm_root_object_alloc(cli->drm->dev);
>> +       if (!r_obj) {
>> +               ret = -ENOMEM;
>> +               goto out_unlock;
>> +       }
>> +
>>          uvmm->kernel_managed_addr = kernel_managed_addr;
>>          uvmm->kernel_managed_size = kernel_managed_size;
>>   
>> -       drm_gpuvm_init(&uvmm->base, cli->name,
>> +       drm_gpuvm_init(&uvmm->base, r_obj, cli->name,
>>                         NOUVEAU_VA_SPACE_START,
>>                         NOUVEAU_VA_SPACE_END,
>>                         kernel_managed_addr, kernel_managed_size,
>>                         NULL);
>> +       /* GPUVM takes care from here on. */
>> +       drm_gem_object_put(r_obj);
>>   
>>          ret = nvif_vmm_ctor(&cli->mmu, "uvmm",
>>                              cli->vmm.vmm.object.oclass, RAW,
>> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
>> index c7ed6bf441d4..0aec14d8b259 100644
>> --- a/include/drm/drm_gpuvm.h
>> +++ b/include/drm/drm_gpuvm.h
>> @@ -238,9 +238,15 @@ struct drm_gpuvm {
>>           * @ops: &drm_gpuvm_ops providing the split/merge steps to
>> drivers
>>           */
>>          const struct drm_gpuvm_ops *ops;
>> +
>> +       /**
>> +        * @r_obj: Root GEM object; representing the GPUVM's common
>> &dma_resv.
>> +        */
>> +       struct drm_gem_object *r_obj;
>>   };
>>   
>> -void drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
>> +void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_gem_object
>> *r_obj,
>> +                   const char *name,
>>                      u64 start_offset, u64 range,
>>                      u64 reserve_offset, u64 reserve_range,
>>                      const struct drm_gpuvm_ops *ops);
>> @@ -248,6 +254,33 @@ void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
>>   
>>   bool drm_gpuvm_interval_empty(struct drm_gpuvm *gpuvm, u64 addr, u64
>> range);
>>   
>> +struct drm_gem_object *
>> +drm_gpuvm_root_object_alloc(struct drm_device *drm);
>> +
>> +/**
>> + * drm_gpuvm_resv() - returns the &drm_gpuvm's &dma_resv
>> + * @gpuvm__: the &drm_gpuvm
>> + *
>> + * Returns: a pointer to the &drm_gpuvm's shared &dma_resv
>> + */
>> +#define drm_gpuvm_resv(gpuvm__) ((gpuvm__)->r_obj->resv)
>> +
>> +/**
>> + * drm_gpuvm_resv_obj() - returns the &drm_gem_object holding the
>> &drm_gpuvm's
>> + * &dma_resv
>> + * @gpuvm__: the &drm_gpuvm
>> + *
>> + * Returns: a pointer to the &drm_gem_object holding the
>> &drm_gpuvm's shared
>> + * &dma_resv
>> + */
>> +#define drm_gpuvm_resv_obj(gpuvm__) ((gpuvm__)->r_obj)
>> +
>> +#define drm_gpuvm_resv_held(gpuvm__) \
>> +       dma_resv_held(drm_gpuvm_resv(gpuvm__))
>> +
>> +#define drm_gpuvm_resv_assert_held(gpuvm__) \
>> +       dma_resv_assert_held(drm_gpuvm_resv(gpuvm__))
>> +
>>   static inline struct drm_gpuva *
>>   __drm_gpuva_next(struct drm_gpuva *va)
>>   {
> 
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> 
>