[Intel-gfx] [PATCH 11/17] 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 | 103 ++++++++++++++++++++++++
 include/uapi/drm/i915_drm.h             |  14 ++++
 2 files changed, 117 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 4e4b0b5c4be0..bac548584091 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -1488,8 +1488,111 @@ static int create_setparam(struct i915_user_extension __user *ext, void *data)
 	return ctx_setparam(data, &local.setparam);
 }
 
+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 create_clone(struct i915_user_extension __user *ext, void *data)
+{
+	struct drm_i915_gem_context_create_ext_clone local;
+	struct i915_gem_context *dst = data;
+	struct i915_gem_context *src;
+	int err;
+
+	if (copy_from_user(&local, ext, sizeof(local)))
+		return -EFAULT;
+
+	if (local.flags & I915_CONTEXT_CLONE_UNKNOWN)
+		return -EINVAL;
+
+	if (local.rsvd)
+		return -EINVAL;
+
+	if (local.clone_id == dst->user_handle) /* good guess! denied. */
+		return -ENOENT;
+
+	rcu_read_lock();
+	src = __i915_gem_context_lookup_rcu(dst->file_priv, local.clone_id);
+	rcu_read_unlock();
+	if (!src)
+		return -ENOENT;
+
+	GEM_BUG_ON(src == dst);
+
+	if (local.flags & I915_CONTEXT_CLONE_FLAGS)
+		dst->user_flags = src->user_flags;
+
+	if (local.flags & I915_CONTEXT_CLONE_SCHED)
+		dst->sched = src->sched;
+
+	if (local.flags & I915_CONTEXT_CLONE_SSEU) {
+		err = clone_sseu(dst, src);
+		if (err)
+			return err;
+	}
+
+	if (local.flags & I915_CONTEXT_CLONE_TIMELINE && src->timeline) {
+		if (dst->timeline)
+			i915_timeline_put(dst->timeline);
+		dst->timeline = i915_timeline_get(src->timeline);
+	}
+
+	if (local.flags & I915_CONTEXT_CLONE_VM) {
+		struct i915_hw_ppgtt *ppgtt;
+
+		do {
+			ppgtt = READ_ONCE(src->ppgtt);
+			if (!ppgtt)
+				break;
+
+			if (!kref_get_unless_zero(&ppgtt->ref))
+				continue;
+
+			if (ppgtt == READ_ONCE(src->ppgtt))
+				break;
+
+			i915_ppgtt_put(ppgtt);
+		} while (1);
+
+		if (ppgtt) {
+			__assign_ppgtt(dst, ppgtt);
+			i915_ppgtt_put(ppgtt);
+		}
+	}
+
+	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 5206d0006043..9714520f43da 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 setparam;
 };
 
+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_SCHED	(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