[PATCH 24/29] drm/i915: Allow multiple user handles to the same VM

[Chris Wilson <chris@chris-wilson.co.uk>]

It was noted that we made the same mistake for VM_ID as for object
handles, whereby we ensured that we only allocated a single handle for
one ppgtt. This has the unfortunate consequence for userspace that they
need to reference count the handles to avoid destroying an active ID. If
we allow multiple handles to the same ppgtt, userspace can freely
unreference any handle they own without fear of destroying the same
handle in use elsewhere.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 26 ++++++++-----------------
 drivers/gpu/drm/i915/i915_gem_gtt.h     |  2 --
 2 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c05f949ed893..2a30cab7a65d 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -837,8 +837,7 @@ int i915_gem_vm_create_ioctl(struct drm_device *dev, void *data,
 	if (err < 0)
 		goto err_unlock;
 
-	GEM_BUG_ON(err == 0); /* reserved for default/unassigned ppgtt */
-	ppgtt->user_handle = err;
+	GEM_BUG_ON(err == 0); /* reserved for invalid/unassigned ppgtt */
 
 	mutex_unlock(&file_priv->vm_idr_lock);
 
@@ -876,10 +875,6 @@ int i915_gem_vm_destroy_ioctl(struct drm_device *dev, void *data,
 		return err;
 
 	ppgtt = idr_remove(&file_priv->vm_idr, id);
-	if (ppgtt) {
-		GEM_BUG_ON(ppgtt->user_handle != id);
-		ppgtt->user_handle = 0;
-	}
 
 	mutex_unlock(&file_priv->vm_idr_lock);
 	if (!ppgtt)
@@ -1001,18 +996,15 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv,
 	if (ret)
 		goto err_put;
 
-	if (!ppgtt->user_handle) {
-		ret = idr_alloc(&file_priv->vm_idr, ppgtt, 0, 0, GFP_KERNEL);
-		GEM_BUG_ON(!ret);
-		if (ret < 0)
-			goto err_unlock;
+	ret = idr_alloc(&file_priv->vm_idr, ppgtt, 0, 0, GFP_KERNEL);
+	GEM_BUG_ON(!ret);
+	if (ret < 0)
+		goto err_unlock;
 
-		ppgtt->user_handle = ret;
-		i915_ppgtt_get(ppgtt);
-	}
+	i915_ppgtt_get(ppgtt);
 
 	args->size = 0;
-	args->value = ppgtt->user_handle;
+	args->value = ret;
 
 	ret = 0;
 err_unlock:
@@ -1103,10 +1095,8 @@ static int set_ppgtt(struct drm_i915_file_private *file_priv,
 		return err;
 
 	ppgtt = idr_find(&file_priv->vm_idr, args->value);
-	if (ppgtt) {
-		GEM_BUG_ON(ppgtt->user_handle != args->value);
+	if (ppgtt)
 		i915_ppgtt_get(ppgtt);
-	}
 	mutex_unlock(&file_priv->vm_idr_lock);
 	if (!ppgtt)
 		return -ENOENT;
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
index c8d96e91f3dc..4832bb5c5fc0 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.h
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
@@ -396,8 +396,6 @@ struct i915_hw_ppgtt {
 		struct i915_page_directory_pointer pdp;	/* GEN8+ */
 		struct i915_page_directory pd;		/* GEN6-7 */
 	};
-
-	u32 user_handle;
 };
 
 struct gen6_hw_ppgtt {
-- 
2.20.1

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