Re: [PATCH 27/32] drm/i915: Allow userspace to clone contexts on creation

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 17/04/2019 08:56, Chris Wilson wrote:
> A usecase arose out of handling context recovery in mesa, whereby they
> wish to recreate a context with fresh logical state but preserving all
> other details of the original. Currently, they create a new context and
> iterate over which bits they want to copy across, but it would much more
> convenient if they were able to just pass in a target context to clone
> during creation. This essentially extends the setparam during creation
> to pull the details from a target context instead of the user supplied
> parameters.
> 
> The ideal here is that we don't expose control over anything more than
> can be obtained via CONTEXT_PARAM. That is userspace retains explicit
> control over all features, and this api is just convenience.
> 
> For example, you could replace
> 
> 	struct context_param p = { .param = CONTEXT_PARAM_VM };
> 
> 	param.ctx_id = old_id;
> 	gem_context_get_param(&p.param);
> 
> 	new_id = gem_context_create();
> 
> 	param.ctx_id = new_id;
> 	gem_context_set_param(&p.param);
> 
> 	gem_vm_destroy(param.value); /* drop the ref to VM_ID handle */
> 
> with
> 
> 	struct create_ext_param p = {
> 	  { .name = CONTEXT_CREATE_CLONE },
> 	  .clone_id = old_id,
> 	  .flags = CLONE_FLAGS_VM
> 	}
> 	new_id = gem_context_create_ext(&p);
> 
> and not have to worry about stray namespace pollution etc.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem_context.c | 206 ++++++++++++++++++++++++
>   include/uapi/drm/i915_drm.h             |  15 ++
>   2 files changed, 221 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index d6bea51050c0..ba7582d955d1 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -1682,8 +1682,214 @@ static int create_setparam(struct i915_user_extension __user *ext, void *data)
>   	return ctx_setparam(arg->fpriv, arg->ctx, &local.param);
>   }
>   
> +static int clone_engines(struct i915_gem_context *dst,
> +			 struct i915_gem_context *src)
> +{
> +	struct i915_gem_engines *e = i915_gem_context_lock_engines(src);
> +	struct i915_gem_engines *clone;
> +	bool user_engines;
> +	unsigned long n;
> +
> +	clone = kmalloc(struct_size(e, engines, e->num_engines), GFP_KERNEL);
> +	if (!clone)
> +		goto err_unlock;
> +
> +	clone->i915 = dst->i915;
> +	for (n = 0; n < e->num_engines; n++) {
> +		if (!e->engines[n]) {
> +			clone->engines[n] = NULL;
> +			continue;
> +		}
> +
> +		clone->engines[n] =
> +			intel_context_create(dst, e->engines[n]->engine);
> +		if (!clone->engines[n]) {
> +			__free_engines(clone, n);
> +			goto err_unlock;
> +		}
> +	}
> +	clone->num_engines = n;
> +
> +	user_engines = i915_gem_context_user_engines(src);
> +	i915_gem_context_unlock_engines(src);
> +
> +	free_engines(dst->engines);
> +	RCU_INIT_POINTER(dst->engines, clone);
> +	if (user_engines)
> +		i915_gem_context_set_user_engines(dst);
> +	else
> +		i915_gem_context_clear_user_engines(dst);
> +	return 0;
> +
> +err_unlock:
> +	i915_gem_context_unlock_engines(src);
> +	return -ENOMEM;
> +}
> +
> +static int clone_flags(struct i915_gem_context *dst,
> +		       struct i915_gem_context *src)
> +{
> +	dst->user_flags = src->user_flags;
> +	return 0;
> +}
> +
> +static int clone_schedattr(struct i915_gem_context *dst,
> +			   struct i915_gem_context *src)
> +{
> +	dst->sched = src->sched;
> +	return 0;
> +}
> +
> +static int clone_sseu(struct i915_gem_context *dst,
> +		      struct i915_gem_context *src)
> +{
> +	struct i915_gem_engines *e = i915_gem_context_lock_engines(src);
> +	struct i915_gem_engines *clone;
> +	unsigned long n;
> +	int err;
> +
> +	clone = dst->engines; /* no locking required; sole access */
> +	if (e->num_engines != clone->num_engines) {
> +		err = -EINVAL;
> +		goto unlock;
> +	}
> +
> +	for (n = 0; n < e->num_engines; n++) {
> +		struct intel_context *ce = e->engines[n];
> +
> +		if (clone->engines[n]->engine->class != ce->engine->class) {
> +			/* Must have compatible engine maps! */
> +			err = -EINVAL;
> +			goto unlock;
> +		}
> +
> +		/* serialises with set_sseu */
> +		err = intel_context_lock_pinned(ce);
> +		if (err)
> +			goto unlock;
> +
> +		clone->engines[n]->sseu = ce->sseu;
> +		intel_context_unlock_pinned(ce);
> +	}
> +
> +	err = 0;
> +unlock:
> +	i915_gem_context_unlock_engines(src);
> +	return err;
> +}
> +
> +static int clone_timeline(struct i915_gem_context *dst,
> +			  struct i915_gem_context *src)
> +{
> +	if (src->timeline) {
> +		GEM_BUG_ON(src->timeline == dst->timeline);
> +
> +		if (dst->timeline)
> +			i915_timeline_put(dst->timeline);
> +		dst->timeline = i915_timeline_get(src->timeline);
> +	}
> +
> +	return 0;
> +}
> +
> +static int clone_vm(struct i915_gem_context *dst,
> +		    struct i915_gem_context *src)
> +{
> +	struct i915_hw_ppgtt *ppgtt;
> +
> +	rcu_read_lock();
> +	do {
> +		ppgtt = READ_ONCE(src->ppgtt);
> +		if (!ppgtt)
> +			break;
> +
> +		if (!kref_get_unless_zero(&ppgtt->ref))
> +			continue;
> +
> +		/*
> +		 * This ppgtt may have be reallocated between
> +		 * the read and the kref, and reassigned to a third
> +		 * context. In order to avoid inadvertent sharing
> +		 * of this ppgtt with that third context (and not
> +		 * src), we have to confirm that we have the same
> +		 * ppgtt after passing through the strong memory
> +		 * barrier implied by a successful
> +		 * kref_get_unless_zero().
> +		 *
> +		 * Once we have acquired the current ppgtt of src,
> +		 * we no longer care if it is released from src, as
> +		 * it cannot be reallocated elsewhere.
> +		 */
> +
> +		if (ppgtt == READ_ONCE(src->ppgtt))
> +			break;
> +
> +		i915_ppgtt_put(ppgtt);
> +	} while (1);
> +	rcu_read_unlock();
> +
> +	if (ppgtt) {
> +		__assign_ppgtt(dst, ppgtt);
> +		i915_ppgtt_put(ppgtt);
> +	}
> +
> +	return 0;
> +}
> +
> +static int create_clone(struct i915_user_extension __user *ext, void *data)
> +{
> +	static int (* const fn[])(struct i915_gem_context *dst,
> +				  struct i915_gem_context *src) = {
> +#define MAP(x, y) [ilog2(I915_CONTEXT_CLONE_##x)] = y
> +		MAP(ENGINES, clone_engines),
> +		MAP(FLAGS, clone_flags),
> +		MAP(SCHEDATTR, clone_schedattr),
> +		MAP(SSEU, clone_sseu),
> +		MAP(TIMELINE, clone_timeline),
> +		MAP(VM, clone_vm),
> +#undef MAP
> +	};
> +	struct drm_i915_gem_context_create_ext_clone local;
> +	const struct create_ext *arg = data;
> +	struct i915_gem_context *dst = arg->ctx;
> +	struct i915_gem_context *src;
> +	int err, bit;
> +
> +	if (copy_from_user(&local, ext, sizeof(local)))
> +		return -EFAULT;
> +
> +	BUILD_BUG_ON(GENMASK(BITS_PER_TYPE(local.flags) - 1, ARRAY_SIZE(fn)) !=
> +		     I915_CONTEXT_CLONE_UNKNOWN);
> +
> +	if (local.flags & I915_CONTEXT_CLONE_UNKNOWN)
> +		return -EINVAL;
> +
> +	if (local.rsvd)
> +		return -EINVAL;
> +
> +	rcu_read_lock();
> +	src = __i915_gem_context_lookup_rcu(arg->fpriv, local.clone_id);
> +	rcu_read_unlock();
> +	if (!src)
> +		return -ENOENT;
> +
> +	GEM_BUG_ON(src == dst);
> +
> +	for (bit = 0; bit < ARRAY_SIZE(fn); bit++) {
> +		if (!(local.flags & BIT(bit)))
> +			continue;
> +
> +		err = fn[bit](dst, src);
> +		if (err)
> +			return err;
> +	}
> +
> +	return 0;
> +}
> +
>   static const i915_user_extension_fn create_extensions[] = {
>   	[I915_CONTEXT_CREATE_EXT_SETPARAM] = create_setparam,
> +	[I915_CONTEXT_CREATE_EXT_CLONE] = create_clone,
>   };
>   
>   static bool client_is_banned(struct drm_i915_file_private *file_priv)
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 7aef672ab3c7..7694113362d4 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -1623,6 +1623,21 @@ struct drm_i915_gem_context_create_ext_setparam {
>   	struct drm_i915_gem_context_param param;
>   };
>   
> +struct drm_i915_gem_context_create_ext_clone {
> +#define I915_CONTEXT_CREATE_EXT_CLONE 1
> +	struct i915_user_extension base;
> +	__u32 clone_id;
> +	__u32 flags;
> +#define I915_CONTEXT_CLONE_ENGINES	(1u << 0)
> +#define I915_CONTEXT_CLONE_FLAGS	(1u << 1)
> +#define I915_CONTEXT_CLONE_SCHEDATTR	(1u << 2)
> +#define I915_CONTEXT_CLONE_SSEU		(1u << 3)
> +#define I915_CONTEXT_CLONE_TIMELINE	(1u << 4)
> +#define I915_CONTEXT_CLONE_VM		(1u << 5)
> +#define I915_CONTEXT_CLONE_UNKNOWN -(I915_CONTEXT_CLONE_VM << 1)
> +	__u64 rsvd;
> +};
> +
>   struct drm_i915_gem_context_destroy {
>   	__u32 ctx_id;
>   	__u32 pad;
> 

Carry over for good measure:

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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