Commit b81dde71 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Allow userspace to clone contexts on creation 



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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190521211134.16117-5-chris@chris-wilson.co.uk
parent 8319f44c

drivers/gpu/drm/i915/i915_gem_context.c

+206 −0
Original line number Diff line number Diff line
@@ -1723,8 +1723,214 @@ 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)

include/uapi/drm/i915_drm.h

+15 −0
Original line number Diff line number Diff line
@@ -1624,6 +1624,21 @@ 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;

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