Re: [PATCH drm-misc-next v3 6/7] drm/gpuvm: generalize dma_resv/extobj handling and GEM validation

Thomas Hellström
2023-09-14T19:14:59Z

On Thu, 2023-09-14 at 19:25 +0200, Danilo Krummrich wrote:
> On 9/14/23 19:21, Thomas Hellström wrote:
> > On Thu, 2023-09-14 at 18:36 +0200, Danilo Krummrich wrote:
> > > On 9/14/23 15:48, Thomas Hellström wrote:
> > > > Hi, Danilo
> > > >
> > > > Some additional minor comments as xe conversion progresses.
> > > >
> > > > On 9/9/23 17:31, Danilo Krummrich wrote:
> > > > > So far the DRM GPUVA manager 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 GPUVA
> > > > > manager
> > > > > represent a basic GPU-VM implementation. 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.
> > > > >
> > > > > Rather than being designed as a "framework", the target is to
> > > > > make all
> > > > > features appear as a collection of optional helper functions,
> > > > > such that
> > > > > drivers are free to make use of the DRM GPUVA managers basic
> > > > > functionality and opt-in for other features without setting
> > > > > any
> > > > > feature
> > > > > flags, just by making use of the corresponding functions.
> > > > >
> > > > > Big kudos 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>
> > > > > ---
> > > > >
> > > > > +/**
> > > > > + * drm_gpuvm_bo_evict() - add / remove a &drm_gem_object to
> > > > > /
> > > > > from a
> > > > > + * &drm_gpuvms evicted list
> > > > > + * @obj: the &drm_gem_object to add or remove
> > > > > + * @evict: indicates whether the object is evicted
> > > > > + *
> > > > > + * Adds a &drm_gem_object to or removes it from all
> > > > > &drm_gpuvms
> > > > > evicted
> > > > > + * list containing a mapping of this &drm_gem_object.
> > > > > + */
> > > > > +void
> > > > > +drm_gpuvm_bo_evict(struct drm_gem_object *obj, bool evict)
> > > > > +{
> > > > > +    struct drm_gpuvm_bo *vm_bo;
> > > > > +
> > > > > +    drm_gem_for_each_gpuvm_bo(vm_bo, obj) {
> > > > > +        if (evict)
> > > > > +            drm_gpuvm_bo_list_add(vm_bo, evict);
> > > > > +        else
> > > > > +            drm_gpuvm_bo_list_del(vm_bo, evict);
> > > > > +    }
> > > > > +}
> > > > > +EXPORT_SYMBOL_GPL(drm_gpuvm_bo_evict);
> > > > > +
> > > >
> > > > We need a drm_gpuvm_bo_evict(struct drm_gpuvm_bo *vm_bo, ...)
> > > > that
> > > > puts a single gpuvm_bo on the list, the above function could
> > > > perhaps be renamed as drm_gpuvm_gem_obj_evict(obj, ....).
> > >
> > > Makes sense - gonna change that.
> > >
> > > >
> > > > Reason is some vm's are faulting vms which don't have an evict
> > > > list, but validate from the pagefault handler. Also evict ==
> > > > false
> > > > is dangerous because if called from within an exec, it might
> > > > remove
> > > > the obj from other vm's evict list before they've had a chance
> > > > to
> > > > rebind their VMAs.
> > > >
> > > > >    static int
> > > > >    __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
> > > > >               struct drm_gpuva *va)
> > > > > diff --git a/include/drm/drm_gpuvm.h
> > > > > b/include/drm/drm_gpuvm.h
> > > > > index afa50b9059a2..834bb6d6617e 100644
> > > > > --- a/include/drm/drm_gpuvm.h
> > > > > +++ b/include/drm/drm_gpuvm.h
> > > > > @@ -26,10 +26,12 @@
> > > > >     */
> > > > >    #include <linux/list.h>
> > > > > +#include <linux/dma-resv.h>
> > > > >    #include <linux/rbtree.h>
> > > > >    #include <linux/types.h>
> > > > >    #include <drm/drm_gem.h>
> > > > > +#include <drm/drm_exec.h>
> > > > >    struct drm_gpuvm;
> > > > >    struct drm_gpuvm_bo;
> > > > > @@ -259,6 +261,38 @@ struct drm_gpuvm {
> > > > >         * space
> > > > >         */
> > > > >        struct dma_resv *resv;
> > > > > +
> > > > > +    /**
> > > > > +     * @extobj: structure holding the extobj list
> > > > > +     */
> > > > > +    struct {
> > > > > +        /**
> > > > > +         * @list: &list_head storing &drm_gpuvm_bos serving
> > > > > as
> > > > > +         * external object
> > > > > +         */
> > > > > +        struct list_head list;
> > > > > +
> > > > > +        /**
> > > > > +         * @lock: spinlock to protect the extobj list
> > > > > +         */
> > > > > +        spinlock_t lock;
> > > > > +    } extobj;
> > > > > +
> > > > > +    /**
> > > > > +     * @evict: structure holding the evict list and evict
> > > > > list
> > > > > lock
> > > > > +     */
> > > > > +    struct {
> > > > > +        /**
> > > > > +         * @list: &list_head storing &drm_gpuvm_bos
> > > > > currently
> > > > > being
> > > > > +         * evicted
> > > > > +         */
> > > > > +        struct list_head list;
> > > > > +
> > > > > +        /**
> > > > > +         * @lock: spinlock to protect the evict list
> > > > > +         */
> > > > > +        spinlock_t lock;
> > > > > +    } evict;
> > > > >    };
> > > > >    void drm_gpuvm_init(struct drm_gpuvm *gpuvm, struct
> > > > > drm_device
> > > > > *drm,
> > > > > @@ -268,6 +302,21 @@ void drm_gpuvm_init(struct drm_gpuvm
> > > > > *gpuvm,
> > > > > struct drm_device *drm,
> > > > >                const struct drm_gpuvm_ops *ops);
> > > > >    void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
> > > > > +/**
> > > > > + * drm_gpuvm_is_extobj() - indicates whether the given
> > > > > &drm_gem_object is an
> > > > > + * external object
> > > > > + * @gpuvm: the &drm_gpuvm to check
> > > > > + * @obj: the &drm_gem_object to check
> > > > > + *
> > > > > + * Returns: true if the &drm_gem_object &dma_resv differs
> > > > > from
> > > > > the
> > > > > + * &drm_gpuvms &dma_resv, false otherwise
> > > > > + */
> > > > > +static inline bool drm_gpuvm_is_extobj(struct drm_gpuvm
> > > > > *gpuvm,
> > > > > +                       struct drm_gem_object *obj)
> > > > > +{
> > > > > +    return obj && obj->resv != gpuvm->resv;
> > > > > +}
> > > > > +
> > > > >    static inline struct drm_gpuva *
> > > > >    __drm_gpuva_next(struct drm_gpuva *va)
> > > > >    {
> > > > > @@ -346,6 +395,128 @@ __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_exec - &drm_gpuvm abstraction of
> > > > > &drm_exec
> > > > > + *
> > > > > + * This structure should be created on the stack as
> > > > > &drm_exec
> > > > > should be.
> > > > > + *
> > > > > + * Optionally, @extra can be set in order to lock additional
> > > > > &drm_gem_objects.
> > > > > + */
> > > > > +struct drm_gpuvm_exec {
> > > > > +    /**
> > > > > +     * @exec: the &drm_exec structure
> > > > > +     */
> > > > > +    struct drm_exec exec;
> > > > > +
> > > > > +    /**
> > > > > +     * @vm: the &drm_gpuvm to lock its DMA reservations
> > > > > +     */
> > > > > +    struct drm_gpuvm *vm;
> > > > > +
> > > > > +    /**
> > > > > +     * @extra: Callback and corresponding private data for
> > > > > the
> > > > > driver to
> > > > > +     * lock arbitrary additional &drm_gem_objects.
> > > > > +     */
> > > > > +    struct {
> > > > > +        /**
> > > > > +         * @fn: The driver callback to lock additional
> > > > > &drm_gem_objects.
> > > > > +         */
> > > > > +        int (*fn)(struct drm_gpuvm_exec *vm_exec,
> > > > > +              unsigned int num_fences);
> > > > > +
> > > > > +        /**
> > > > > +         * @priv: driver private data for the @fn callback
> > > > > +         */
> > > > > +        void *priv;
> > > > > +    } extra;
> > > > > +};
> > > > > +
> > > > > +/**
> > > > > + * drm_gpuvm_prepare_vm() - prepare the GPUVMs common dma-
> > > > > resv
> > > > > + * @gpuvm: the &drm_gpuvm
> > > > > + * @exec: the &drm_exec context
> > > > > + * @num_fences: the amount of &dma_fences to reserve
> > > > > + *
> > > > > + * Calls drm_exec_prepare_obj() for the GPUVMs dummy
> > > > > &drm_gem_object.
> > > > > + *
> > > > > + * Using this function directly, it is the drivers
> > > > > responsibility to call
> > > > > + * drm_exec_init() and drm_exec_fini() accordingly.
> > > > > + *
> > > > > + * Returns: 0 on success, negative error code on failure.
> > > > > + */
> > > > > +static inline int
> > > > > +drm_gpuvm_prepare_vm(struct drm_gpuvm *gpuvm,
> > > > > +             struct drm_exec *exec,
> > > > > +             unsigned int num_fences)
> > > > > +{
> > > > > +    return drm_exec_prepare_obj(exec, &gpuvm->d_obj,
> > > > > num_fences);
> > > > > +}
> > > > > +
> > > > > +int drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
> > > > > +                  struct drm_exec *exec,
> > > > > +                  unsigned int num_fences);
> > > > > +
> > > > > +int drm_gpuvm_prepare_range(struct drm_gpuvm *gpuvm,
> > > > > +                struct drm_exec *exec,
> > > > > +                u64 addr, u64 range,
> > > > > +                unsigned int num_fences);
> > > > > +
> > > > > +int drm_gpuvm_exec_lock(struct drm_gpuvm_exec *vm_exec,
> > > > > +            unsigned int num_fences,
> > > > > +            bool interruptible);
> > > > > +
> > > > > +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);
> > > > > +
> > > > > +int drm_gpuvm_exec_lock_range(struct drm_gpuvm_exec
> > > > > *vm_exec,
> > > > > +                  u64 addr, u64 range,
> > > > > +                  unsigned int num_fences,
> > > > > +                  bool interruptible);
> > > > > +
> > > > > +/**
> > > > > + * drm_gpuvm_lock() - lock all dma-resv of all assoiciated
> > > > > BOs
> > > > > + * @gpuvm: the &drm_gpuvm
> > > > > + *
> > > > > + * Releases all dma-resv locks of all &drm_gem_objects
> > > > > previously acquired
> > > > > + * through drm_gpuvm_lock() or its variants.
> > > > > + *
> > > > > + * Returns: 0 on success, negative error code on failure.
> > > > > + */
> > > > > +static inline void
> > > > > +drm_gpuvm_exec_unlock(struct drm_gpuvm_exec *vm_exec)
> > > > > +{
> > > > > +    drm_exec_fini(&vm_exec->exec);
> > > > > +}
> > > > > +
> > > > > +int drm_gpuvm_validate(struct drm_gpuvm *gpuvm);
> > > > > +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);
> > > > > +
> > > > > +/**
> > > > > + * drm_gpuvm_exec_resv_add_fence()
> > > > > + * @vm_exec: the &drm_gpuvm_exec abstraction
> > > > > + * @fence: fence to add
> > > > > + * @private_usage: private dma-resv usage
> > > > > + * @extobj_usage: extobj dma-resv usage
> > > > > + *
> > > > > + * See drm_gpuvm_resv_add_fence().
> > > > > + */
> > > > > +static inline void
> > > > > +drm_gpuvm_exec_resv_add_fence(struct drm_gpuvm_exec
> > > > > *vm_exec,
> > > > > +                  struct dma_fence *fence,
> > > > > +                  enum dma_resv_usage private_usage,
> > > > > +                  enum dma_resv_usage extobj_usage)
> > > > > +{
> > > > > +    drm_gpuvm_resv_add_fence(vm_exec->vm, &vm_exec->exec,
> > > > > fence,
> > > > > +                 private_usage, extobj_usage);
> > > > > +}
> > > > > +
> > > > >    /**
> > > > >     * struct drm_gpuvm_bo - structure representing a
> > > > > &drm_gpuvm
> > > > > and
> > > > >     * &drm_gem_object combination
> > > > > @@ -398,6 +569,18 @@ struct drm_gpuvm_bo {
> > > > >                 * gpuva list.
> > > > >                 */
> > > > >                struct list_head gem;
> > > > > +
> > > > > +            /**
> > > > > +             * @evict: List entry to attach to the
> > > > > &drm_gpuvms
> > > > > +             * extobj list.
> > > > > +             */
> > > > > +            struct list_head extobj;
> > > > > +
> > > > > +            /**
> > > > > +             * @evict: List entry to attach to the
> > > > > &drm_gpuvms
> > > > > evict
> > > > > +             * list.
> > > > > +             */
> > > > > +            struct list_head evict;
> > > > >            } entry;
> > > > >        } list;
> > > > >    };
> > > > > @@ -432,6 +615,9 @@ struct drm_gpuvm_bo *
> > > > >    drm_gpuvm_bo_find(struct drm_gpuvm *gpuvm,
> > > > >              struct drm_gem_object *obj);
> > > > > +void drm_gpuvm_bo_evict(struct drm_gem_object *obj, bool
> > > > > evict);
> > > > > +void drm_gpuvm_bo_extobj_add(struct drm_gpuvm_bo *vm_bo);
> > > > > +
> > > > >    /**
> > > > >     * drm_gpuvm_bo_for_each_va() - iterator to walk over a
> > > > > list of
> > > > > &drm_gpuva
> > > > >     * @va__: &drm_gpuva structure to assign to in each
> > > > > iteration
> > > > > step
> > > > > @@ -837,6 +1023,17 @@ struct drm_gpuvm_ops {
> > > > >         * used.
> > > > >         */
> > > > >        int (*sm_step_unmap)(struct drm_gpuva_op *op, void
> > > > > *priv);
> > > > > +
> > > > > +    /**
> > > > > +     * @bo_validate: called from drm_gpuvm_validate()
> > > > > +     *
> > > > > +     * Drivers receive this callback for every evicted
> > > > > &drm_gem_object being
> > > > > +     * mapped in the corresponding &drm_gpuvm.
> > > > > +     *
> > > > > +     * Typically, drivers would call their driver specific
> > > > > variant of
> > > > > +     * ttm_bo_validate() from within this callback.
> > > > > +     */
> > > > > +    int (*bo_validate)(struct drm_gem_object *obj);
> > > >
> > > > Same here. Could we have a vm_bo as an argument instead, so
> > > > that
> > > > the callback knows what gpuvm we're targeting and can mark all
> > > > its
> > > > gpu_vas for revalidation? Or is that intended to be done
> > > > elsewhere?
> > >
> > > Makes sense as well. I'll change that too.
> >
> > I forgot, drm_gpuvm_validate() would preferably take an
> > drm_gpuvm_exec
> > argument because we need it in the validate callback. It's also
> > easy
> > for the driver to subclass further if needed, to pass even more
> > arguments to its validate callback.
>
> Hm.. that implies that a driver open coding the drm_exec loop, still
> needs
> to use a struct drm_gpuvm_exec rather than just a struct drm_exec.
> What is
> this needed for in Xe? Do we expect other drivers needing it? Might a
> priv
> void pointer maybe make more sense?

It's for sleeping locks during eviction rather than trylocks. TTM
currently fishes out the struct ww_acquire_context used for locking
from the lock itself, but I'd expect that to be more explicit in the
near future with a variant of ttm_bo_validate() that actually
explicitly takes a drm_exec as argument.

So we would probably also like to try to find a way to encourage
drivers to include the validate() in the until_all_locked() loop,
because if TTM resorts to a sleeping lock *after* that loop, the
following warning will be hit:

https://elixir.bootlin.com/linux/latest/source/kernel/locking/ww_mutex.h#L195

So not sure what's best, but perhaps then a struct drm_exec * or a
(void *)

/Thomas

>
> >
> > /Thomas
> >
> >
> > >
> > > >
> > > > >    };
> > > > >    int drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm, void *priv,
> > > >
> > > > Thanks,
> > > >
> > > > Thomas
> > > >
> > > >
> > >
> >
>