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Message-ID: <be93d9ef-3d3e-4262-a280-d2922b983ca1@amd.com>
Date: Fri, 3 Nov 2023 08:18:35 +0100
From: Christian König <christian.koenig@....com>
To: Danilo Krummrich <dakr@...hat.com>, airlied@...il.com,
daniel@...ll.ch, matthew.brost@...el.com,
thomas.hellstrom@...ux.intel.com, sarah.walker@...tec.com,
donald.robson@...tec.com, boris.brezillon@...labora.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 v8 09/12] drm/gpuvm: reference count
drm_gpuvm structures
Am 02.11.23 um 00:31 schrieb Danilo Krummrich:
> Implement reference counting for struct drm_gpuvm.
From the design point of view what is that good for?
Background is that the most common use case I see is that this object is
embedded into something else and a reference count is then not really a
good idea.
Thanks,
Christian.
>
> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> ---
> drivers/gpu/drm/drm_gpuvm.c | 44 +++++++++++++++++++-------
> drivers/gpu/drm/nouveau/nouveau_uvmm.c | 20 +++++++++---
> include/drm/drm_gpuvm.h | 31 +++++++++++++++++-
> 3 files changed, 78 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
> index 53e2c406fb04..6a88eafc5229 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -746,6 +746,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
> gpuvm->rb.tree = RB_ROOT_CACHED;
> INIT_LIST_HEAD(&gpuvm->rb.list);
>
> + kref_init(&gpuvm->kref);
> +
> gpuvm->name = name ? name : "unknown";
> gpuvm->flags = flags;
> gpuvm->ops = ops;
> @@ -770,15 +772,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
> }
> EXPORT_SYMBOL_GPL(drm_gpuvm_init);
>
> -/**
> - * drm_gpuvm_destroy() - cleanup a &drm_gpuvm
> - * @gpuvm: pointer to the &drm_gpuvm to clean up
> - *
> - * Note that it is a bug to call this function on a manager that still
> - * holds GPU VA mappings.
> - */
> -void
> -drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
> +static void
> +drm_gpuvm_fini(struct drm_gpuvm *gpuvm)
> {
> gpuvm->name = NULL;
>
> @@ -790,7 +785,33 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
>
> drm_gem_object_put(gpuvm->r_obj);
> }
> -EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
> +
> +static void
> +drm_gpuvm_free(struct kref *kref)
> +{
> + struct drm_gpuvm *gpuvm = container_of(kref, struct drm_gpuvm, kref);
> +
> + if (drm_WARN_ON(gpuvm->drm, !gpuvm->ops->vm_free))
> + return;
> +
> + drm_gpuvm_fini(gpuvm);
> +
> + gpuvm->ops->vm_free(gpuvm);
> +}
> +
> +/**
> + * drm_gpuvm_bo_put() - drop a struct drm_gpuvm reference
> + * @gpuvm: the &drm_gpuvm to release the reference of
> + *
> + * This releases a reference to @gpuvm.
> + */
> +void
> +drm_gpuvm_put(struct drm_gpuvm *gpuvm)
> +{
> + if (gpuvm)
> + kref_put(&gpuvm->kref, drm_gpuvm_free);
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_put);
>
> static int
> __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> @@ -843,7 +864,7 @@ drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> if (unlikely(!drm_gpuvm_range_valid(gpuvm, addr, range)))
> return -EINVAL;
>
> - return __drm_gpuva_insert(gpuvm, va);
> + return __drm_gpuva_insert(drm_gpuvm_get(gpuvm), va);
> }
> EXPORT_SYMBOL_GPL(drm_gpuva_insert);
>
> @@ -876,6 +897,7 @@ drm_gpuva_remove(struct drm_gpuva *va)
> }
>
> __drm_gpuva_remove(va);
> + drm_gpuvm_put(va->vm);
> }
> EXPORT_SYMBOL_GPL(drm_gpuva_remove);
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> index 54be12c1272f..cb2f06565c46 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> @@ -1780,6 +1780,18 @@ nouveau_uvmm_bo_unmap_all(struct nouveau_bo *nvbo)
> }
> }
>
> +static void
> +nouveau_uvmm_free(struct drm_gpuvm *gpuvm)
> +{
> + struct nouveau_uvmm *uvmm = uvmm_from_gpuvm(gpuvm);
> +
> + kfree(uvmm);
> +}
> +
> +static const struct drm_gpuvm_ops gpuvm_ops = {
> + .vm_free = nouveau_uvmm_free,
> +};
> +
> int
> nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
> void *data,
> @@ -1830,7 +1842,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
> NOUVEAU_VA_SPACE_END,
> init->kernel_managed_addr,
> init->kernel_managed_size,
> - NULL);
> + &gpuvm_ops);
> /* GPUVM takes care from here on. */
> drm_gem_object_put(r_obj);
>
> @@ -1849,8 +1861,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
> return 0;
>
> out_gpuvm_fini:
> - drm_gpuvm_destroy(&uvmm->base);
> - kfree(uvmm);
> + drm_gpuvm_put(&uvmm->base);
> out_unlock:
> mutex_unlock(&cli->mutex);
> return ret;
> @@ -1902,7 +1913,6 @@ nouveau_uvmm_fini(struct nouveau_uvmm *uvmm)
>
> mutex_lock(&cli->mutex);
> nouveau_vmm_fini(&uvmm->vmm);
> - drm_gpuvm_destroy(&uvmm->base);
> - kfree(uvmm);
> + drm_gpuvm_put(&uvmm->base);
> mutex_unlock(&cli->mutex);
> }
> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> index 0c2e24155a93..4e6e1fd3485a 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -247,6 +247,11 @@ struct drm_gpuvm {
> struct list_head list;
> } rb;
>
> + /**
> + * @kref: reference count of this object
> + */
> + struct kref kref;
> +
> /**
> * @kernel_alloc_node:
> *
> @@ -273,7 +278,23 @@ void drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
> u64 start_offset, u64 range,
> u64 reserve_offset, u64 reserve_range,
> const struct drm_gpuvm_ops *ops);
> -void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
> +
> +/**
> + * drm_gpuvm_get() - acquire a struct drm_gpuvm reference
> + * @gpuvm: the &drm_gpuvm to acquire the reference of
> + *
> + * This function acquires an additional reference to @gpuvm. It is illegal to
> + * call this without already holding a reference. No locks required.
> + */
> +static inline struct drm_gpuvm *
> +drm_gpuvm_get(struct drm_gpuvm *gpuvm)
> +{
> + kref_get(&gpuvm->kref);
> +
> + return gpuvm;
> +}
> +
> +void drm_gpuvm_put(struct drm_gpuvm *gpuvm);
>
> bool drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm, u64 addr, u64 range);
> bool drm_gpuvm_interval_empty(struct drm_gpuvm *gpuvm, u64 addr, u64 range);
> @@ -673,6 +694,14 @@ static inline void drm_gpuva_init_from_op(struct drm_gpuva *va,
> * operations to drivers.
> */
> struct drm_gpuvm_ops {
> + /**
> + * @vm_free: called when the last reference of a struct drm_gpuvm is
> + * dropped
> + *
> + * This callback is mandatory.
> + */
> + void (*vm_free)(struct drm_gpuvm *gpuvm);
> +
> /**
> * @op_alloc: called when the &drm_gpuvm allocates
> * a struct drm_gpuva_op
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