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    SubjectRe: [PATCH drm-misc-next v4 4/8] drm/gpuvm: add common dma-resv per struct drm_gpuvm
    From
    Am 20.09.23 um 16:42 schrieb Danilo Krummrich:
    > 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 | 9 +++++++--
    > drivers/gpu/drm/nouveau/nouveau_uvmm.c | 2 +-
    > include/drm/drm_gpuvm.h | 17 ++++++++++++++++-
    > 3 files changed, 24 insertions(+), 4 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
    > index bfea4a8a19ec..cbf4b738a16c 100644
    > --- a/drivers/gpu/drm/drm_gpuvm.c
    > +++ b/drivers/gpu/drm/drm_gpuvm.c
    > @@ -655,6 +655,7 @@ drm_gpuva_range_valid(struct drm_gpuvm *gpuvm,
    > /**
    > * drm_gpuvm_init() - initialize a &drm_gpuvm
    > * @gpuvm: pointer to the &drm_gpuvm to initialize
    > + * @drm: the drivers &drm_device
    > * @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 +669,7 @@ drm_gpuva_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_device *drm,
    > const char *name,
    > u64 start_offset, u64 range,
    > u64 reserve_offset, u64 reserve_range,
    > @@ -694,6 +695,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm,
    > reserve_range)))
    > __drm_gpuva_insert(gpuvm, &gpuvm->kernel_alloc_node);
    > }
    > +
    > + drm_gem_private_object_init(drm, &gpuvm->d_obj, 0);
    > }
    > EXPORT_SYMBOL_GPL(drm_gpuvm_init);
    >
    > @@ -713,7 +716,9 @@ 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");
    > +
    > + drm_gem_private_object_fini(&gpuvm->d_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 6c86b64273c3..a80ac8767843 100644
    > --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
    > +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
    > @@ -1836,7 +1836,7 @@ nouveau_uvmm_init(struct nouveau_uvmm *uvmm, struct nouveau_cli *cli,
    > 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, cli->drm->dev, cli->name,
    > NOUVEAU_VA_SPACE_START,
    > NOUVEAU_VA_SPACE_END,
    > kernel_managed_addr, kernel_managed_size,
    > diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
    > index 0e802676e0a9..6666c07d7c3e 100644
    > --- a/include/drm/drm_gpuvm.h
    > +++ b/include/drm/drm_gpuvm.h
    > @@ -240,14 +240,29 @@ struct drm_gpuvm {
    > * @ops: &drm_gpuvm_ops providing the split/merge steps to drivers
    > */
    > const struct drm_gpuvm_ops *ops;
    > +
    > + /**
    > + * @d_obj: Dummy GEM object; used internally to pass the GPU VMs
    > + * dma-resv to &drm_exec. Provides the GPUVM's &dma-resv.
    > + */
    > + struct drm_gem_object d_obj;

    Yeah, as pointed out in the other mail that won't work like this.

    The GPUVM contains GEM objects and therefore should probably have a
    reference to those objects.

    When those GEM objects now use the dma-resv object embedded inside the
    GPUVM then they also need a reference to the GPUVM to make sure the
    dma-resv object won't be freed before they are freed.

    This is a circle reference dependency.

    The simplest solution I can see is to let the driver provide the GEM
    object to use. Amdgpu uses the root page directory object for this.

    Apart from that I strongly think that we shouldn't let the GPUVM code
    create a driver GEM object. We did that in TTM for the ghost objects and
    it turned out to be a bad idea.

    Regards,
    Christian.

    > };
    >
    > -void drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
    > +void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct drm_device *drm,
    > + 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_resv() - returns the &drm_gpuvm's &dma_resv
    > + * @gpuvm__: the &drm_gpuvm
    > + *
    > + * Returns: a pointer to the &drm_gpuvm's &dma_resv
    > + */
    > +#define drm_gpuvm_resv(gpuvm__) (&(gpuvm__)->d_obj._resv)
    > +
    > static inline struct drm_gpuva *
    > __drm_gpuva_next(struct drm_gpuva *va)
    > {

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