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Message-ID: <25ac1a025060f7aeb5af363124c6919d7742e8cf.camel@linux.intel.com>
Date: Wed, 01 Nov 2023 17:38:46 +0100
From: Thomas Hellström
<thomas.hellstrom@...ux.intel.com>
To: Danilo Krummrich <dakr@...hat.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: nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH drm-misc-next v7 4/7] drm/gpuvm: add an abstraction for
a VM / BO combination
On Tue, 2023-10-31 at 18:38 +0100, Danilo Krummrich wrote:
> On 10/31/23 11:32, Thomas Hellström wrote:
> > On Mon, 2023-10-23 at 22:16 +0200, Danilo Krummrich wrote:
> > > Add an abstraction layer between the drm_gpuva mappings of a
> > > particular
> > > drm_gem_object and this GEM object itself. The abstraction
> > > represents
> > > a
> > > combination of a drm_gem_object and drm_gpuvm. The drm_gem_object
> > > holds
> > > a list of drm_gpuvm_bo structures (the structure representing
> > > this
> > > abstraction), while each drm_gpuvm_bo contains list of mappings
> > > of
> > > this
> > > GEM object.
> > >
> > > This has multiple advantages:
> > >
> > > 1) We can use the drm_gpuvm_bo structure to attach it to various
> > > lists
> > > of the drm_gpuvm. This is useful for tracking external and
> > > evicted
> > > objects per VM, which is introduced in subsequent patches.
> > >
> > > 2) Finding mappings of a certain drm_gem_object mapped in a
> > > certain
> > > drm_gpuvm becomes much cheaper.
> > >
> > > 3) Drivers can derive and extend the structure to easily
> > > represent
> > > driver specific states of a BO for a certain GPUVM.
> > >
> > > The idea of this abstraction was taken from amdgpu, hence the
> > > credit
> > > for
> > > this idea goes to the developers of amdgpu.
> > >
> > > Cc: Christian König <christian.koenig@....com>
> > > Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> > > ---
> > > drivers/gpu/drm/drm_gpuvm.c | 335
> > > +++++++++++++++++++++--
> > > --
> > > drivers/gpu/drm/nouveau/nouveau_uvmm.c | 64 +++--
> > > include/drm/drm_gem.h | 32 +--
> > > include/drm/drm_gpuvm.h | 188 +++++++++++++-
> > > 4 files changed, 533 insertions(+), 86 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_gpuvm.c
> > > b/drivers/gpu/drm/drm_gpuvm.c
> > > index c03332883432..7f4f5919f84c 100644
> > > --- a/drivers/gpu/drm/drm_gpuvm.c
> > > +++ b/drivers/gpu/drm/drm_gpuvm.c
> > > @@ -70,6 +70,18 @@
> > > * &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_resv_object_alloc().
> > > + *
> > > + * In order to connect a struct drm_gpuva its backing
> > > &drm_gem_object each
> > > + * &drm_gem_object maintains a list of &drm_gpuvm_bo structures,
> > > and
> > > each
> > > + * &drm_gpuvm_bo contains a list of &drm_gpuva structures.
> > > + *
> > > + * A &drm_gpuvm_bo is an abstraction that represents a
> > > combination
> > > of a
> > > + * &drm_gpuvm and a &drm_gem_object. Every such combination
> > > should
> > > be unique.
> > > + * This is ensured by the API through drm_gpuvm_bo_obtain() and
> > > + * drm_gpuvm_bo_obtain_prealloc() which first look into the
> > > corresponding
> > > + * &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.
> > > */
> > >
> > > /**
> > > @@ -395,21 +407,28 @@
> > > /**
> > > * DOC: Locking
> > > *
> > > - * Generally, the GPU VA manager does not take care of locking
> > > itself, it is
> > > - * the drivers responsibility to take care about locking.
> > > Drivers
> > > might want to
> > > - * protect the following operations: inserting, removing and
> > > iterating
> > > - * &drm_gpuva objects as well as generating all kinds of
> > > operations,
> > > such as
> > > - * split / merge or prefetch.
> > > - *
> > > - * The GPU VA manager also does not take care of the locking of
> > > the
> > > backing
> > > - * &drm_gem_object buffers GPU VA lists by itself; drivers are
> > > responsible to
> > > - * enforce mutual exclusion using either the GEMs dma_resv lock
> > > or
> > > alternatively
> > > - * a driver specific external lock. For the latter see also
> > > - * drm_gem_gpuva_set_lock().
> > > - *
> > > - * However, the GPU VA manager contains lockdep checks to ensure
> > > callers of its
> > > - * API hold the corresponding lock whenever the &drm_gem_objects
> > > GPU
> > > VA list is
> > > - * accessed by functions such as drm_gpuva_link() or
> > > drm_gpuva_unlink().
> > > + * In terms of managing &drm_gpuva entries DRM GPUVM does not
> > > take
> > > care of
> > > + * locking itself, it is the drivers responsibility to take care
> > > about locking.
> > > + * Drivers might want to protect the following operations:
> > > inserting, removing
> > > + * and iterating &drm_gpuva objects as well as generating all
> > > kinds
> > > of
> > > + * operations, such as split / merge or prefetch.
> > > + *
> > > + * DRM GPUVM also does not take care of the locking of the
> > > backing
> > > + * &drm_gem_object buffers GPU VA lists and &drm_gpuvm_bo
> > > abstractions by
> > > + * itself; drivers are responsible to enforce mutual exclusion
> > > using
> > > either the
> > > + * GEMs dma_resv lock or alternatively a driver specific
> > > external
> > > lock. For the
> > > + * latter see also drm_gem_gpuva_set_lock().
> > > + *
> > > + * However, DRM GPUVM contains lockdep checks to ensure callers
> > > of
> > > its API hold
> > > + * the corresponding lock whenever the &drm_gem_objects GPU VA
> > > list
> > > is accessed
> > > + * by functions such as drm_gpuva_link() or drm_gpuva_unlink(),
> > > but
> > > also
> > > + * drm_gpuvm_bo_obtain() and drm_gpuvm_bo_put().
> > > + *
> > > + * The latter is required since on creation and destruction of a
> > > &drm_gpuvm_bo
> > > + * the &drm_gpuvm_bo is attached / removed from the
> > > &drm_gem_objects
> > > gpuva list.
> > > + * 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.
> > > */
> > >
> > > /**
> > > @@ -439,6 +458,7 @@
> > > * {
> > > * struct drm_gpuva_ops *ops;
> > > * struct drm_gpuva_op *op
> > > + * struct drm_gpuvm_bo *vm_bo;
> > > *
> > > * driver_lock_va_space();
> > > * ops = drm_gpuvm_sm_map_ops_create(gpuvm, addr,
> > > range,
> > > @@ -446,6 +466,10 @@
> > > * if (IS_ERR(ops))
> > > * return PTR_ERR(ops);
> > > *
> > > + * vm_bo = drm_gpuvm_bo_obtain(gpuvm, obj);
> > > + * if (IS_ERR(vm_bo))
> > > + * return PTR_ERR(vm_bo);
> > > + *
> > > * drm_gpuva_for_each_op(op, ops) {
> > > * struct drm_gpuva *va;
> > > *
> > > @@ -458,7 +482,7 @@
> > > *
> > > * driver_vm_map();
> > > * drm_gpuva_map(gpuvm, va, &op-
> > > >map);
> > > - * drm_gpuva_link(va);
> > > + * drm_gpuva_link(va, vm_bo);
> > > *
> > > * break;
> > > * case DRM_GPUVA_OP_REMAP: {
> > > @@ -485,11 +509,11 @@
> > > * driver_vm_remap();
> > > * drm_gpuva_remap(prev, next, &op-
> > > > remap);
> > > *
> > > - * drm_gpuva_unlink(va);
> > > * if (prev)
> > > - * drm_gpuva_link(prev);
> > > + * drm_gpuva_link(prev, va-
> > > > vm_bo);
> > > * if (next)
> > > - * drm_gpuva_link(next);
> > > + * drm_gpuva_link(next, va-
> > > > vm_bo);
> > > + * drm_gpuva_unlink(va);
> > > *
> > > * break;
> > > * }
> > > @@ -505,6 +529,7 @@
> > > * break;
> > > * }
> > > * }
> > > + * drm_gpuvm_bo_put(vm_bo);
> > > * driver_unlock_va_space();
> > > *
> > > * return 0;
> > > @@ -514,6 +539,7 @@
> > > *
> > > * struct driver_context {
> > > * struct drm_gpuvm *gpuvm;
> > > + * struct drm_gpuvm_bo *vm_bo;
> > > * struct drm_gpuva *new_va;
> > > * struct drm_gpuva *prev_va;
> > > * struct drm_gpuva *next_va;
> > > @@ -534,6 +560,7 @@
> > > * struct drm_gem_object *obj,
> > > u64
> > > offset)
> > > * {
> > > * struct driver_context ctx;
> > > + * struct drm_gpuvm_bo *vm_bo;
> > > * struct drm_gpuva_ops *ops;
> > > * struct drm_gpuva_op *op;
> > > * int ret = 0;
> > > @@ -543,16 +570,23 @@
> > > * ctx.new_va = kzalloc(sizeof(*ctx.new_va),
> > > GFP_KERNEL);
> > > * ctx.prev_va = kzalloc(sizeof(*ctx.prev_va),
> > > GFP_KERNEL);
> > > * ctx.next_va = kzalloc(sizeof(*ctx.next_va),
> > > GFP_KERNEL);
> > > - * if (!ctx.new_va || !ctx.prev_va || !ctx.next_va)
> > > {
> > > + * ctx.vm_bo = drm_gpuvm_bo_create(gpuvm, obj);
> > > + * if (!ctx.new_va || !ctx.prev_va || !ctx.next_va
> > > ||
> > > !vm_bo) {
> > > * ret = -ENOMEM;
> > > * goto out;
> > > * }
> > > *
> > > + * // Typically protected with a driver specific GEM
> > > gpuva lock
> > > + * // used in the fence signaling path for
> > > drm_gpuva_link() and
> > > + * // drm_gpuva_unlink(), hence pre-allocate.
> > > + * ctx.vm_bo =
> > > drm_gpuvm_bo_obtain_prealloc(ctx.vm_bo);
> > > + *
> > > * driver_lock_va_space();
> > > * ret = drm_gpuvm_sm_map(gpuvm, &ctx, addr, range,
> > > obj,
> > > offset);
> > > * driver_unlock_va_space();
> > > *
> > > * out:
> > > + * drm_gpuvm_bo_put(ctx.vm_bo);
> > > * kfree(ctx.new_va);
> > > * kfree(ctx.prev_va);
> > > * kfree(ctx.next_va);
> > > @@ -565,7 +599,7 @@
> > > *
> > > * drm_gpuva_map(ctx->vm, ctx->new_va, &op->map);
> > > *
> > > - * drm_gpuva_link(ctx->new_va);
> > > + * drm_gpuva_link(ctx->new_va, ctx->vm_bo);
> > > *
> > > * // prevent the new GPUVA from being freed in
> > > * // driver_mapping_create()
> > > @@ -577,22 +611,23 @@
> > > * int driver_gpuva_remap(struct drm_gpuva_op *op, void
> > > *__ctx)
> > > * {
> > > * struct driver_context *ctx = __ctx;
> > > + * struct drm_gpuva *va = op->remap.unmap->va;
> > > *
> > > * drm_gpuva_remap(ctx->prev_va, ctx->next_va, &op-
> > > > remap);
> > > *
> > > - * drm_gpuva_unlink(op->remap.unmap->va);
> > > - * kfree(op->remap.unmap->va);
> > > - *
> > > * if (op->remap.prev) {
> > > - * drm_gpuva_link(ctx->prev_va);
> > > + * drm_gpuva_link(ctx->prev_va, va->vm_bo);
> > > * ctx->prev_va = NULL;
> > > * }
> > > *
> > > * if (op->remap.next) {
> > > - * drm_gpuva_link(ctx->next_va);
> > > + * drm_gpuva_link(ctx->next_va, va->vm_bo);
> > > * ctx->next_va = NULL;
> > > * }
> > > *
> > > + * drm_gpuva_unlink(va);
> > > + * kfree(va);
> > > + *
> > > * return 0;
> > > * }
> > > *
> > > @@ -774,6 +809,194 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
> > > }
> > > EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
> > >
> > > +/**
> > > + * drm_gpuvm_bo_create() - create a new instance of struct
> > > drm_gpuvm_bo
> > > + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
> > > + * @obj: The &drm_gem_object being mapped in the @gpuvm.
> > > + *
> > > + * If provided by the driver, this function uses the
> > > &drm_gpuvm_ops
> > > + * vm_bo_alloc() callback to allocate.
> > > + *
> > > + * Returns: a pointer to the &drm_gpuvm_bo on success, NULL on
> >
> > Still needs s/Returns:/Return:/g
> >
> > > failure
> > > + */
> > > +struct drm_gpuvm_bo *
> > > +drm_gpuvm_bo_create(struct drm_gpuvm *gpuvm,
> > > + struct drm_gem_object *obj)
> > > +{
> > > + const struct drm_gpuvm_ops *ops = gpuvm->ops;
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > + if (ops && ops->vm_bo_alloc)
> > > + vm_bo = ops->vm_bo_alloc();
> > > + else
> > > + vm_bo = kzalloc(sizeof(*vm_bo), GFP_KERNEL);
> > > +
> > > + if (unlikely(!vm_bo))
> > > + return NULL;
> > > +
> > > + vm_bo->vm = gpuvm;
> > > + vm_bo->obj = obj;
> > > + drm_gem_object_get(obj);
> > > +
> > > + kref_init(&vm_bo->kref);
> > > + INIT_LIST_HEAD(&vm_bo->list.gpuva);
> > > + INIT_LIST_HEAD(&vm_bo->list.entry.gem);
> > > +
> > > + return vm_bo;
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_create);
> > > +
> > > +static void
> > > +drm_gpuvm_bo_destroy(struct kref *kref)
> > > +{
> > > + struct drm_gpuvm_bo *vm_bo = container_of(kref, struct
> > > drm_gpuvm_bo,
> > > + kref);
> > > + struct drm_gpuvm *gpuvm = vm_bo->vm;
> > > + const struct drm_gpuvm_ops *ops = gpuvm->ops;
> > > + struct drm_gem_object *obj = vm_bo->obj;
> > > + bool lock = !drm_gpuvm_resv_protected(gpuvm);
> > > +
> > > + if (!lock)
> > > + drm_gpuvm_resv_assert_held(gpuvm);
> > > +
> > > + drm_gem_gpuva_assert_lock_held(obj);
> > > + list_del(&vm_bo->list.entry.gem);
> > > +
> > > + if (ops && ops->vm_bo_free)
> > > + ops->vm_bo_free(vm_bo);
> > > + else
> > > + kfree(vm_bo);
> > > +
> > > + drm_gem_object_put(obj);
> > > +}
> > > +
> > > +/**
> > > + * drm_gpuvm_bo_put() - drop a struct drm_gpuvm_bo reference
> > > + * @vm_bo: the &drm_gpuvm_bo to release the reference of
> > > + *
> > > + * This releases a reference to @vm_bo.
> > > + *
> > > + * If the reference count drops to zero, the &gpuvm_bo is
> > > destroyed,
> > > which
> > > + * includes removing it from the GEMs gpuva list. Hence, if a
> > > call
> > > to this
> > > + * function can potentially let the reference count to zero the
> > > caller must
> > > + * hold the dma-resv or driver specific GEM gpuva lock.
> > > + */
> > > +void
> > > +drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo)
> > > +{
> > > + if (vm_bo)
> > > + kref_put(&vm_bo->kref, drm_gpuvm_bo_destroy);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_put);
> > > +
> > > +static struct drm_gpuvm_bo *
> > > +__drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> > > + struct drm_gem_object *obj)
> > > +{
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > + drm_gem_gpuva_assert_lock_held(obj);
> > > + drm_gem_for_each_gpuvm_bo(vm_bo, obj)
> > > + if (vm_bo->vm == gpuvm)
> > > + return vm_bo;
> > > +
> > > + return NULL;
> > > +}
> > > +
> > > +/**
> > > + * drm_gpuvm_bo_find() - find the &drm_gpuvm_bo for the given
> > > + * &drm_gpuvm and &drm_gem_object
> > > + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
> > > + * @obj: The &drm_gem_object being mapped in the @gpuvm.
> > > + *
> > > + * Find the &drm_gpuvm_bo representing the combination of the
> > > given
> > > + * &drm_gpuvm and &drm_gem_object. If found, increases the
> > > reference
> > > + * count of the &drm_gpuvm_bo accordingly.
> > > + *
> > > + * Returns: a pointer to the &drm_gpuvm_bo on success, NULL on
> > > failure
> > > + */
> > > +struct drm_gpuvm_bo *
> > > +drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> > > + struct drm_gem_object *obj)
> > > +{
> > > + struct drm_gpuvm_bo *vm_bo = __drm_gpuvm_bo_find(gpuvm,
> > > obj);
> > > +
> > > + return vm_bo ? drm_gpuvm_bo_get(vm_bo) : NULL;
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_find);
> > > +
> > > +/**
> > > + * drm_gpuvm_bo_obtain() - obtains and instance of the
> > > &drm_gpuvm_bo
> > > for the
> > > + * given &drm_gpuvm and &drm_gem_object
> > > + * @gpuvm: The &drm_gpuvm the @obj is mapped in.
> > > + * @obj: The &drm_gem_object being mapped in the @gpuvm.
> > > + *
> > > + * Find the &drm_gpuvm_bo representing the combination of the
> > > given
> > > + * &drm_gpuvm and &drm_gem_object. If found, increases the
> > > reference
> > > + * count of the &drm_gpuvm_bo accordingly. If not found,
> > > allocates a
> > > new
> > > + * &drm_gpuvm_bo.
> > > + *
> > > + * A new &drm_gpuvm_bo is added to the GEMs gpuva list.
> > > + *
> > > + * Returns: a pointer to the &drm_gpuvm_bo on success, an
> > > ERR_PTR on
> > > failure
> > > + */
> > > +struct drm_gpuvm_bo *
> > > +drm_gpuvm_bo_obtain(struct drm_gpuvm *gpuvm,
> > > + struct drm_gem_object *obj)
> > > +{
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > + vm_bo = drm_gpuvm_bo_find(gpuvm, obj);
> > > + if (vm_bo)
> > > + return vm_bo;
> > > +
> > > + vm_bo = drm_gpuvm_bo_create(gpuvm, obj);
> > > + if (!vm_bo)
> > > + return ERR_PTR(-ENOMEM);
> > > +
> > > + drm_gem_gpuva_assert_lock_held(obj);
> > > + list_add_tail(&vm_bo->list.entry.gem, &obj->gpuva.list);
> > > +
> > > + return vm_bo;
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain);
> > > +
> > > +/**
> > > + * drm_gpuvm_bo_obtain_prealloc() - obtains and instance of the
> > > &drm_gpuvm_bo
> > > + * for the given &drm_gpuvm and &drm_gem_object
> > > + * @__vm_bo: A pre-allocated struct drm_gpuvm_bo.
> > > + *
> > > + * Find the &drm_gpuvm_bo representing the combination of the
> > > given
> > > + * &drm_gpuvm and &drm_gem_object. If found, increases the
> > > reference
> > > + * count of the found &drm_gpuvm_bo accordingly, while the
> > > @__vm_bo
> > > reference
> > > + * count is decreased. If not found @__vm_bo is returned without
> > > further
> > > + * increase of the reference count.
> > > + *
> > > + * A new &drm_gpuvm_bo is added to the GEMs gpuva list.
> > > + *
> > > + * Returns: a pointer to the found &drm_gpuvm_bo or @__vm_bo if
> > > no
> > > existing
> > > + * &drm_gpuvm_bo was found
> > > + */
> > > +struct drm_gpuvm_bo *
> > > +drm_gpuvm_bo_obtain_prealloc(struct drm_gpuvm_bo *__vm_bo)
> > > +{
> > > + struct drm_gpuvm *gpuvm = __vm_bo->vm;
> > > + struct drm_gem_object *obj = __vm_bo->obj;
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > + vm_bo = drm_gpuvm_bo_find(gpuvm, obj);
> > > + if (vm_bo) {
> > > + drm_gpuvm_bo_put(__vm_bo);
> > > + return vm_bo;
> > > + }
> > > +
> > > + drm_gem_gpuva_assert_lock_held(obj);
> > > + list_add_tail(&__vm_bo->list.entry.gem, &obj-
> > > >gpuva.list);
> > > +
> > > + return __vm_bo;
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_obtain_prealloc);
> > > +
> > > static int
> > > __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> > > struct drm_gpuva *va)
> > > @@ -864,24 +1087,33 @@ EXPORT_SYMBOL_GPL(drm_gpuva_remove);
> > > /**
> > > * drm_gpuva_link() - link a &drm_gpuva
> > > * @va: the &drm_gpuva to link
> > > + * @vm_bo: the &drm_gpuvm_bo to add the &drm_gpuva to
> > > *
> > > - * This adds the given &va to the GPU VA list of the
> > > &drm_gem_object
> > > it is
> > > - * associated with.
> > > + * This adds the given &va to the GPU VA list of the
> > > &drm_gpuvm_bo
> > > and the
> > > + * &drm_gpuvm_bo to the &drm_gem_object it is associated with.
> > > + *
> > > + * For every &drm_gpuva entry added to the &drm_gpuvm_bo an
> > > additional
> > > + * reference of the latter is taken.
> > > *
> > > * This function expects the caller to protect the GEM's GPUVA
> > > list
> > > against
> > > - * concurrent access using the GEMs dma_resv lock.
> > > + * concurrent access using either the GEMs dma_resv lock or a
> > > driver
> > > specific
> > > + * lock set through drm_gem_gpuva_set_lock().
> > > */
> > > void
> > > -drm_gpuva_link(struct drm_gpuva *va)
> > > +drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuvm_bo *vm_bo)
> > > {
> > > struct drm_gem_object *obj = va->gem.obj;
> > > + struct drm_gpuvm *gpuvm = va->vm;
> > >
> > > if (unlikely(!obj))
> > > return;
> > >
> > > - drm_gem_gpuva_assert_lock_held(obj);
> > > + drm_WARN_ON(gpuvm->drm, obj != vm_bo->obj);
> > >
> > > - list_add_tail(&va->gem.entry, &obj->gpuva.list);
> > > + va->vm_bo = drm_gpuvm_bo_get(vm_bo);
> > > +
> > > + drm_gem_gpuva_assert_lock_held(obj);
> > > + list_add_tail(&va->gem.entry, &vm_bo->list.gpuva);
> > > }
> > > EXPORT_SYMBOL_GPL(drm_gpuva_link);
> > >
> > > @@ -892,20 +1124,31 @@ EXPORT_SYMBOL_GPL(drm_gpuva_link);
> > > * This removes the given &va from the GPU VA list of the
> > > &drm_gem_object it is
> > > * associated with.
> > > *
> > > + * This removes the given &va from the GPU VA list of the
> > > &drm_gpuvm_bo and
> > > + * the &drm_gpuvm_bo from the &drm_gem_object it is associated
> > > with
> > > in case
> > > + * this call unlinks the last &drm_gpuva from the &drm_gpuvm_bo.
> > > + *
> > > + * For every &drm_gpuva entry removed from the &drm_gpuvm_bo a
> > > reference of
> > > + * the latter is dropped.
> > > + *
> > > * This function expects the caller to protect the GEM's GPUVA
> > > list
> > > against
> > > - * concurrent access using the GEMs dma_resv lock.
> > > + * concurrent access using either the GEMs dma_resv lock or a
> > > driver
> > > specific
> > > + * lock set through drm_gem_gpuva_set_lock().
> > > */
> > > void
> > > drm_gpuva_unlink(struct drm_gpuva *va)
> > > {
> > > struct drm_gem_object *obj = va->gem.obj;
> > > + struct drm_gpuvm_bo *vm_bo = va->vm_bo;
> > >
> > > if (unlikely(!obj))
> > > return;
> > >
> > > drm_gem_gpuva_assert_lock_held(obj);
> > > -
> > > list_del_init(&va->gem.entry);
> > > +
> > > + va->vm_bo = NULL;
> > > + drm_gpuvm_bo_put(vm_bo);
> > > }
> > > EXPORT_SYMBOL_GPL(drm_gpuva_unlink);
> > >
> > > @@ -1050,10 +1293,10 @@ drm_gpuva_remap(struct drm_gpuva *prev,
> > > struct drm_gpuva *next,
> > > struct drm_gpuva_op_remap *op)
> > > {
> > > - struct drm_gpuva *curr = op->unmap->va;
> > > - struct drm_gpuvm *gpuvm = curr->vm;
> > > + struct drm_gpuva *va = op->unmap->va;
> > > + struct drm_gpuvm *gpuvm = va->vm;
> > >
> > > - drm_gpuva_remove(curr);
> > > + drm_gpuva_remove(va);
> > >
> > > if (op->prev) {
> > > drm_gpuva_init_from_op(prev, op->prev);
> > > @@ -1695,9 +1938,8 @@ drm_gpuvm_prefetch_ops_create(struct
> > > drm_gpuvm
> > > *gpuvm,
> > > EXPORT_SYMBOL_GPL(drm_gpuvm_prefetch_ops_create);
> > >
> > > /**
> > > - * drm_gpuvm_gem_unmap_ops_create() - creates the &drm_gpuva_ops
> > > to
> > > unmap a GEM
> > > - * @gpuvm: the &drm_gpuvm representing the GPU VA space
> > > - * @obj: the &drm_gem_object to unmap
> > > + * drm_gpuvm_bo_unmap_ops_create() - creates the &drm_gpuva_ops
> > > to
> > > unmap a GEM
> > > + * @vm_bo: the &drm_gpuvm_bo abstraction
> > > *
> > > * This function creates a list of operations to perform
> > > unmapping
> > > for every
> > > * GPUVA attached to a GEM.
> > > @@ -1714,15 +1956,14 @@
> > > EXPORT_SYMBOL_GPL(drm_gpuvm_prefetch_ops_create);
> > > * Returns: a pointer to the &drm_gpuva_ops on success, an
> > > ERR_PTR
> > > on failure
> > > */
> > > struct drm_gpuva_ops *
> > > -drm_gpuvm_gem_unmap_ops_create(struct drm_gpuvm *gpuvm,
> > > - struct drm_gem_object *obj)
> > > +drm_gpuvm_bo_unmap_ops_create(struct drm_gpuvm_bo *vm_bo)
> > > {
> > > struct drm_gpuva_ops *ops;
> > > struct drm_gpuva_op *op;
> > > struct drm_gpuva *va;
> > > int ret;
> > >
> > > - drm_gem_gpuva_assert_lock_held(obj);
> > > + drm_gem_gpuva_assert_lock_held(vm_bo->obj);
> > >
> > > ops = kzalloc(sizeof(*ops), GFP_KERNEL);
> > > if (!ops)
> > > @@ -1730,8 +1971,8 @@ drm_gpuvm_gem_unmap_ops_create(struct
> > > drm_gpuvm
> > > *gpuvm,
> > >
> > > INIT_LIST_HEAD(&ops->list);
> > >
> > > - drm_gem_for_each_gpuva(va, obj) {
> > > - op = gpuva_op_alloc(gpuvm);
> > > + drm_gpuvm_bo_for_each_va(va, vm_bo) {
> > > + op = gpuva_op_alloc(vm_bo->vm);
> > > if (!op) {
> > > ret = -ENOMEM;
> > > goto err_free_ops;
> > > @@ -1745,10 +1986,10 @@ drm_gpuvm_gem_unmap_ops_create(struct
> > > drm_gpuvm *gpuvm,
> > > return ops;
> > >
> > > err_free_ops:
> > > - drm_gpuva_ops_free(gpuvm, ops);
> > > + drm_gpuva_ops_free(vm_bo->vm, ops);
> > > return ERR_PTR(ret);
> > > }
> > > -EXPORT_SYMBOL_GPL(drm_gpuvm_gem_unmap_ops_create);
> > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_unmap_ops_create);
> > >
> > > /**
> > > * drm_gpuva_ops_free() - free the given &drm_gpuva_ops
> > > diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> > > b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> > > index ed439bf4032f..1e95b0a1b047 100644
> > > --- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> > > +++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
> > > @@ -62,6 +62,8 @@ struct bind_job_op {
> > > enum vm_bind_op op;
> > > u32 flags;
> > >
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > struct {
> > > u64 addr;
> > > u64 range;
> > > @@ -1113,22 +1115,28 @@ bind_validate_region(struct nouveau_job
> > > *job)
> > > }
> > >
> > > static void
> > > -bind_link_gpuvas(struct drm_gpuva_ops *ops, struct
> > > nouveau_uvma_prealloc *new)
> > > +bind_link_gpuvas(struct bind_job_op *bop)
> > > {
> > > + struct nouveau_uvma_prealloc *new = &bop->new;
> > > + struct drm_gpuvm_bo *vm_bo = bop->vm_bo;
> > > + struct drm_gpuva_ops *ops = bop->ops;
> > > struct drm_gpuva_op *op;
> > >
> > > drm_gpuva_for_each_op(op, ops) {
> > > switch (op->op) {
> > > case DRM_GPUVA_OP_MAP:
> > > - drm_gpuva_link(&new->map->va);
> > > + drm_gpuva_link(&new->map->va, vm_bo);
> > > break;
> > > - case DRM_GPUVA_OP_REMAP:
> > > + case DRM_GPUVA_OP_REMAP: {
> > > + struct drm_gpuva *va = op->remap.unmap-
> > > >va;
> > > +
> > > if (op->remap.prev)
> > > - drm_gpuva_link(&new->prev->va);
> > > + drm_gpuva_link(&new->prev->va,
> > > va-
> > > > vm_bo);
> > > if (op->remap.next)
> > > - drm_gpuva_link(&new->next->va);
> > > - drm_gpuva_unlink(op->remap.unmap->va);
> > > + drm_gpuva_link(&new->next->va,
> > > va-
> > > > vm_bo);
> > > + drm_gpuva_unlink(va);
> > > break;
> > > + }
> > > case DRM_GPUVA_OP_UNMAP:
> > > drm_gpuva_unlink(op->unmap.va);
> > > break;
> > > @@ -1150,10 +1158,18 @@ nouveau_uvmm_bind_job_submit(struct
> > > nouveau_job *job)
> > >
> > > list_for_each_op(op, &bind_job->ops) {
> > > if (op->op == OP_MAP) {
> > > - op->gem.obj = drm_gem_object_lookup(job-
> > > > file_priv,
> > > - op-
> > > > gem.handle);
> > > - if (!op->gem.obj)
> > > + struct drm_gem_object *obj;
> > > +
> > > + obj = drm_gem_object_lookup(job-
> > > >file_priv,
> > > + op-
> > > >gem.handle);
> > > + if (!(op->gem.obj = obj))
> > > return -ENOENT;
> > > +
> > > + dma_resv_lock(obj->resv, NULL);
> > > + op->vm_bo = drm_gpuvm_bo_obtain(&uvmm-
> > > >base,
> > > obj);
> > > + dma_resv_unlock(obj->resv);
> > > + if (IS_ERR(op->vm_bo))
> > > + return PTR_ERR(op->vm_bo);
> > > }
> > >
> > > ret = bind_validate_op(job, op);
> > > @@ -1364,7 +1380,7 @@ nouveau_uvmm_bind_job_submit(struct
> > > nouveau_job
> > > *job)
> > > case OP_UNMAP_SPARSE:
> > > case OP_MAP:
> > > case OP_UNMAP:
> > > - bind_link_gpuvas(op->ops, &op->new);
> > > + bind_link_gpuvas(op);
> > > break;
> > > default:
> > > break;
> > > @@ -1511,6 +1527,12 @@ nouveau_uvmm_bind_job_free_work_fn(struct
> > > work_struct *work)
> > > if (!IS_ERR_OR_NULL(op->ops))
> > > drm_gpuva_ops_free(&uvmm->base, op-
> > > >ops);
> > >
> > > + if (!IS_ERR_OR_NULL(op->vm_bo)) {
> > > + dma_resv_lock(obj->resv, NULL);
> > > + drm_gpuvm_bo_put(op->vm_bo);
> > > + dma_resv_unlock(obj->resv);
> > > + }
> > > +
> > > if (obj)
> > > drm_gem_object_put(obj);
> > > }
> > > @@ -1776,15 +1798,18 @@ void
> > > nouveau_uvmm_bo_map_all(struct nouveau_bo *nvbo, struct
> > > nouveau_mem
> > > *mem)
> > > {
> > > struct drm_gem_object *obj = &nvbo->bo.base;
> > > + struct drm_gpuvm_bo *vm_bo;
> > > struct drm_gpuva *va;
> > >
> > > dma_resv_assert_held(obj->resv);
> > >
> > > - drm_gem_for_each_gpuva(va, obj) {
> > > - struct nouveau_uvma *uvma = uvma_from_va(va);
> > > + drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
> > > + drm_gpuvm_bo_for_each_va(va, vm_bo) {
> > > + struct nouveau_uvma *uvma =
> > > uvma_from_va(va);
> > >
> > > - nouveau_uvma_map(uvma, mem);
> > > - drm_gpuva_invalidate(va, false);
> > > + nouveau_uvma_map(uvma, mem);
> > > + drm_gpuva_invalidate(va, false);
> > > + }
> > > }
> > > }
> > >
> > > @@ -1792,15 +1817,18 @@ void
> > > nouveau_uvmm_bo_unmap_all(struct nouveau_bo *nvbo)
> > > {
> > > struct drm_gem_object *obj = &nvbo->bo.base;
> > > + struct drm_gpuvm_bo *vm_bo;
> > > struct drm_gpuva *va;
> > >
> > > dma_resv_assert_held(obj->resv);
> > >
> > > - drm_gem_for_each_gpuva(va, obj) {
> > > - struct nouveau_uvma *uvma = uvma_from_va(va);
> > > + drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
> > > + drm_gpuvm_bo_for_each_va(va, vm_bo) {
> > > + struct nouveau_uvma *uvma =
> > > uvma_from_va(va);
> > >
> > > - �� nouveau_uvma_unmap(uvma);
> > > - drm_gpuva_invalidate(va, true);
> > > + nouveau_uvma_unmap(uvma);
> > > + drm_gpuva_invalidate(va, true);
> > > + }
> > > }
> > > }
> > >
> > > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> > > index 16364487fde9..369505447acd 100644
> > > --- a/include/drm/drm_gem.h
> > > +++ b/include/drm/drm_gem.h
> > > @@ -580,7 +580,7 @@ int drm_gem_evict(struct drm_gem_object
> > > *obj);
> > > * drm_gem_gpuva_init() - initialize the gpuva list of a GEM
> > > object
> > > * @obj: the &drm_gem_object
> > > *
> > > - * This initializes the &drm_gem_object's &drm_gpuva list.
> > > + * This initializes the &drm_gem_object's &drm_gpuvm_bo list.
> > > *
> > > * Calling this function is only necessary for drivers
> > > intending to
> > > support the
> > > * &drm_driver_feature DRIVER_GEM_GPUVA.
> > > @@ -593,28 +593,28 @@ static inline void
> > > drm_gem_gpuva_init(struct
> > > drm_gem_object *obj)
> > > }
> > >
> > > /**
> > > - * drm_gem_for_each_gpuva() - iternator to walk over a list of
> > > gpuvas
> > > - * @entry__: &drm_gpuva structure to assign to in each iteration
> > > step
> > > - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are
> > > associated with
> > > + * drm_gem_for_each_gpuvm_bo() - iterator to walk over a list of
> > > &drm_gpuvm_bo
> > > + * @entry__: &drm_gpuvm_bo structure to assign to in each
> > > iteration
> > > step
> > > + * @obj__: the &drm_gem_object the &drm_gpuvm_bo to walk are
> > > associated with
> > > *
> > > - * This iterator walks over all &drm_gpuva structures associated
> > > with the
> > > - * &drm_gpuva_manager.
> > > + * This iterator walks over all &drm_gpuvm_bo structures
> > > associated
> > > with the
> > > + * &drm_gem_object.
> > > */
> > > -#define drm_gem_for_each_gpuva(entry__, obj__) \
> > > - list_for_each_entry(entry__, &(obj__)->gpuva.list,
> > > gem.entry)
> > > +#define drm_gem_for_each_gpuvm_bo(entry__, obj__) \
> > > + list_for_each_entry(entry__, &(obj__)->gpuva.list,
> > > list.entry.gem)
> > >
> > > /**
> > > - * drm_gem_for_each_gpuva_safe() - iternator to safely walk over
> > > a
> > > list of
> > > - * gpuvas
> > > - * @entry__: &drm_gpuva structure to assign to in each iteration
> > > step
> > > - * @next__: &next &drm_gpuva to store the next step
> > > - * @obj__: the &drm_gem_object the &drm_gpuvas to walk are
> > > associated with
> > > + * drm_gem_for_each_gpuvm_bo_safe() - iterator to safely walk
> > > over a
> > > list of
> > > + * &drm_gpuvm_bo
> > > + * @entry__: &drm_gpuvm_bostructure to assign to in each
> > > iteration
> > > step
> > > + * @next__: &next &drm_gpuvm_bo to store the next step
> > > + * @obj__: the &drm_gem_object the &drm_gpuvm_bo to walk are
> > > associated with
> > > *
> > > - * This iterator walks over all &drm_gpuva structures associated
> > > with the
> > > + * This iterator walks over all &drm_gpuvm_bo structures
> > > associated
> > > with the
> > > * &drm_gem_object. It is implemented with
> > > list_for_each_entry_safe(), hence
> > > * it is save against removal of elements.
> > > */
> > > -#define drm_gem_for_each_gpuva_safe(entry__, next__, obj__) \
> > > - list_for_each_entry_safe(entry__, next__, &(obj__)-
> > > > gpuva.list, gem.entry)
> > > +#define drm_gem_for_each_gpuvm_bo_safe(entry__, next__, obj__) \
> > > + list_for_each_entry_safe(entry__, next__, &(obj__)-
> > > > gpuva.list, list.entry.gem)
> > >
> > > #endif /* __DRM_GEM_H__ */
> > > diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> > > index 47cbacb244b9..466fdd76c71a 100644
> > > --- a/include/drm/drm_gpuvm.h
> > > +++ b/include/drm/drm_gpuvm.h
> > > @@ -25,6 +25,7 @@
> > > * OTHER DEALINGS IN THE SOFTWARE.
> > > */
> > >
> > > +#include <linux/dma-resv.h>
> > > #include <linux/list.h>
> > > #include <linux/rbtree.h>
> > > #include <linux/types.h>
> > > @@ -33,6 +34,7 @@
> > > #include <drm/drm_gem.h>
> > >
> > > struct drm_gpuvm;
> > > +struct drm_gpuvm_bo;
> > > struct drm_gpuvm_ops;
> > >
> > > /**
> > > @@ -73,6 +75,12 @@ struct drm_gpuva {
> > > */
> > > struct drm_gpuvm *vm;
> > >
> > > + /**
> > > + * @vm_bo: the &drm_gpuvm_bo abstraction for the mapped
> > > + * &drm_gem_object
> > > + */
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > /**
> > > * @flags: the &drm_gpuva_flags for this mapping
> > > */
> > > @@ -108,7 +116,7 @@ struct drm_gpuva {
> > > struct drm_gem_object *obj;
> > >
> > > /**
> > > - * @entry: the &list_head to attach this object
> > > to a
> > > &drm_gem_object
> > > + * @entry: the &list_head to attach this object
> > > to a
> > > &drm_gpuvm_bo
> > > */
> > > struct list_head entry;
> > > } gem;
> > > @@ -141,7 +149,7 @@ struct drm_gpuva {
> > > int drm_gpuva_insert(struct drm_gpuvm *gpuvm, struct drm_gpuva
> > > *va);
> > > void drm_gpuva_remove(struct drm_gpuva *va);
> > >
> > > -void drm_gpuva_link(struct drm_gpuva *va);
> > > +void drm_gpuva_link(struct drm_gpuva *va, struct drm_gpuvm_bo
> > > *vm_bo);
> > > void drm_gpuva_unlink(struct drm_gpuva *va);
> > >
> > > struct drm_gpuva *drm_gpuva_find(struct drm_gpuvm *gpuvm,
> > > @@ -188,10 +196,16 @@ static inline bool
> > > drm_gpuva_invalidated(struct
> > > drm_gpuva *va)
> > > * enum drm_gpuvm_flags - flags for struct drm_gpuvm
> > > */
> > > enum drm_gpuvm_flags {
> > > + /**
> > > + * @DRM_GPUVM_RESV_PROTECTED: GPUVM is protected
> > > externally
> > > by the
> > > + * GPUVM's &dma_resv lock
> > > + */
> > > + DRM_GPUVM_RESV_PROTECTED = BIT(0),
> > > +
> > > /**
> > > * @DRM_GPUVM_USERBITS: user defined bits
> > > */
> > > - DRM_GPUVM_USERBITS = BIT(0),
> > > + DRM_GPUVM_USERBITS = BIT(1),
> > > };
> > >
> > > /**
> > > @@ -280,6 +294,19 @@ bool drm_gpuvm_interval_empty(struct
> > > drm_gpuvm
> > > *gpuvm, u64 addr, u64 range);
> > > struct drm_gem_object *
> > > drm_gpuvm_resv_object_alloc(struct drm_device *drm);
> > >
> > > +/**
> > > + * drm_gpuvm_resv_protected() - indicates whether
> > > &DRM_GPUVM_RESV_PROTECTED is
> > > + * set
> > > + * @gpuvm: the &drm_gpuvm
> > > + *
> > > + * Returns: true if &DRM_GPUVM_RESV_PROTECTED is set, false
> > > otherwise.
> > > + */
> > > +static inline bool
> > > +drm_gpuvm_resv_protected(struct drm_gpuvm *gpuvm)
> > > +{
> > > + return gpuvm->flags & DRM_GPUVM_RESV_PROTECTED;
> > > +}
> > > +
> > > /**
> > > * drm_gpuvm_resv() - returns the &drm_gpuvm's &dma_resv
> > > * @gpuvm__: the &drm_gpuvm
> > > @@ -298,6 +325,12 @@ drm_gpuvm_resv_object_alloc(struct
> > > drm_device
> > > *drm);
> > > */
> > > #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__))
> > > +
> > > #define drm_gpuvm_resv_held(gpuvm__) \
> > > dma_resv_held(drm_gpuvm_resv(gpuvm__))
> > >
> > > @@ -382,6 +415,128 @@ __drm_gpuva_next(struct drm_gpuva *va)
> > > #define drm_gpuvm_for_each_va_safe(va__, next__, gpuvm__) \
> > > list_for_each_entry_safe(va__, next__, &(gpuvm__)-
> > > >rb.list,
> > > rb.entry)
> > >
> > > +/**
> > > + * struct drm_gpuvm_bo - structure representing a &drm_gpuvm and
> > > + * &drm_gem_object combination
> > > + *
> > > + * This structure is an abstraction representing a &drm_gpuvm
> > > and
> > > + * &drm_gem_object combination. It serves as an indirection to
> > > accelerate
> > > + * iterating all &drm_gpuvas within a &drm_gpuvm backed by the
> > > same
> > > + * &drm_gem_object.
> > > + *
> > > + * Furthermore it is used cache evicted GEM objects for a
> > > certain
> > > GPU-VM to
> > > + * accelerate validation.
> > > + *
> > > + * Typically, drivers want to create an instance of a struct
> > > drm_gpuvm_bo once
> > > + * a GEM object is mapped first in a GPU-VM and release the
> > > instance
> > > once the
> > > + * last mapping of the GEM object in this GPU-VM is unmapped.
> > > + */
> > > +struct drm_gpuvm_bo {
> > > + /**
> > > + * @vm: The &drm_gpuvm the @obj is mapped in. This
> > > pointer is
> > > not
> > > + * reference counted.
> > > + *
> > > + * A struct drm_gpuvm_bo is not allowed to out-live its
> > > &drm_gpuvm
> > > + * context. Implicitly, this is ensured by the fact that
> > > the
> > > driver is
> > > + * responsible to ensure the VM doesn't contain mappings
> > > once
> > > it's
> > > + * freed, since a struct drm_gpuvm_bo should be freed
> > > once
> > > the last
> > > + * mapping being backed by the corresponding buffer
> > > object is
> > > unmapped.
> > > + */
> >
> >
> > I don't think the above is completely true. Let's assume in the
> > !RESV_PROTECTED case that a reference is grabbed on the
> > drm_gpuvm_bo
> > during an iteration over a list. Then user-space closes the vm and
> > all
> > vmas are unlinked, but this reference remains but the vm pointer
> > becomes stale. In the RESV_PROTECTED case this is ensured not to
> > happen
> > if by the vm->resv being grabbed during unlink, but in the
> > !RESV_PROTECTED case, the above wording isn't sufficient. The
> > caller
> > needs to ensure the vm stays alive using some sort of similar rule
> > or
> > use kref_get_unless_zero() on the vm under the spinlock if
> > dereferenced.
>
> The list is part of the GPUVM. Hence, the caller *must* either
> already hold
> a reference to the GPUVM or otherwise ensure it's not freed while
> iterating
> this list. All the drm_gpuvm_bo structures within this list can't
> have a
> pointer to another VM than this one by definition.
>
> Anyway, I recognize that this isn't very obvious. Hence, I think we
> should
> probably reference count GPUVMs as well. I'd think of the same way we
> do it
> with drm_gem_objects. However, I'd prefer to introduce this with a
> subsequent
> patch.
Well, I think we should actually be OK in most cases, and refcounting
here would probably result in circular dependencies.
I think to do this properly one would document that this pointer is not
refecounted and that dereferencing that pointer requires a strong vm
reference from elsewhere, or holding the bo resv and verifying that the
gpuvm_bo is on the gem object's gpuvm_bo list.
We've had a lot of tricky lifetime problems of vms and vmas in the i915
driver so that's why I think clearly documenting the rules for
dereferencing is important. In particular if we, in the future provide
some sort of iteration over the gem object's gpvum_bo list, dropping
the lock while iterating, that will blow up.
/Thomas
>
> >
> > > + struct drm_gpuvm *vm;
> > > +
> > > + /**
> > > + * @obj: The &drm_gem_object being mapped in @vm. This is
> > > a
> > > reference
> > > + * counted pointer.
> > > + */
> > > + struct drm_gem_object *obj;
> > > +
> > > + /**
> > > + * @kref: The reference count for this &drm_gpuvm_bo.
> > > + */
> > > + struct kref kref;
> > > +
> > > + /**
> > > + * @list: Structure containing all &list_heads.
> > > + */
> > > + struct {
> > > + /**
> > > + * @gpuva: The list of linked &drm_gpuvas.
> > > + */
> > > + struct list_head gpuva;
> >
> > Still missing doc on how the @gpuva stays alive during iteration
> > over
> > the list?
>
> Thanks for pointing this out again, I missed that one.
>
> - Danilo
>
> >
> >
> >
> > 8<-------------------------------------------------------------
> >
> > Thanks,
> > Thomas
> >
>
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