[Intel-gfx] [PATCH] drm/i915: Allow userspace to clone contexts on creation

[Chris Wilson]

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.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 154 ++++++++++++++++++++++++
 include/uapi/drm/i915_drm.h             |  14 +++
 2 files changed, 168 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 57b4e760fa4b..1972f112d72b 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -1513,8 +1513,162 @@ static int create_setparam(struct i915_user_extension __user *ext, void *data)
 	return ctx_setparam(arg->ctx, &local.param);
 }
 
+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)
+{
+	const struct intel_sseu default_sseu =
+		intel_device_default_sseu(dst->i915);
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+
+	for_each_engine(engine, dst->i915, id) {
+		struct intel_context *ce;
+		struct intel_sseu sseu;
+
+		ce = intel_context_lookup(src, engine);
+		if (!ce)
+			continue;
+
+		sseu = ce->sseu;
+		if (!memcmp(&sseu, &default_sseu, sizeof(sseu)))
+			continue;
+
+		ce = intel_context_pin_lock(dst, engine);
+		if (IS_ERR(ce))
+			return PTR_ERR(ce);
+
+		ce->sseu = sseu;
+		intel_context_pin_unlock(ce);
+	}
+
+	return 0;
+}
+
+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(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 9999f7d6a5a9..a5bdb86858f6 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1581,6 +1581,20 @@ 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_FLAGS	(1u << 0)
+#define I915_CONTEXT_CLONE_SCHEDATTR	(1u << 1)
+#define I915_CONTEXT_CLONE_SSEU		(1u << 2)
+#define I915_CONTEXT_CLONE_TIMELINE	(1u << 3)
+#define I915_CONTEXT_CLONE_VM		(1u << 4)
+#define I915_CONTEXT_CLONE_UNKNOWN -(I915_CONTEXT_CLONE_VM << 1)
+	__u64 rsvd;
+};
+
 struct drm_i915_gem_context_destroy {
 	__u32 ctx_id;
 	__u32 pad;
-- 
2.20.1