drm/i915: Allow multiple user handles to the same VM

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 <[email protected]>
Reviewed-by: Tvrtko Ursulin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 8 insertions, 18 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 76ed74e75d82..05496ea7a123 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -772,8 +772,7 @@ 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);
 
@@ -811,10 +810,6 @@ 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)
@@ -925,18 +920,15 @@ 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:
@@ -1027,10 +1019,8 @@ 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;