drm/i915: Create a global list of vms

After we plumb our code to support multiple address spaces (VMs), there
are a few situations where we want to be able to traverse the list of
all address spaces in the system. Cases like eviction, or error state
collection are obvious example.

v2: Delete the global link instead of the list head. While this in and
of itself shouldn't be really be a problem, doing this allows us to WARN
on an non-empty list, which is a problem. (Daniel)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1492,6 +1492,10 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 
 	i915_dump_device_info(dev_priv);
 
+	INIT_LIST_HEAD(&dev_priv->vm_list);
+	INIT_LIST_HEAD(&dev_priv->gtt.base.global_link);
+	list_add(&dev_priv->gtt.base.global_link, &dev_priv->vm_list);
+
 	if (i915_get_bridge_dev(dev)) {
 		ret = -EIO;
 		goto free_priv;
@@ -1758,6 +1762,8 @@ int i915_driver_unload(struct drm_device *dev)
 			i915_free_hws(dev);
 	}
 
+	list_del(&dev_priv->gtt.base.global_link);
+	WARN_ON(!list_empty(&dev_priv->vm_list));
 	drm_mm_takedown(&dev_priv->gtt.base.mm);
 	if (dev_priv->regs != NULL)
 		pci_iounmap(dev->pdev, dev_priv->regs);

drivers/gpu/drm/i915/i915_drv.h

@@ -449,6 +449,7 @@ typedef uint32_t gen6_gtt_pte_t;
 struct i915_address_space {
 	struct drm_mm mm;
 	struct drm_device *dev;
+	struct list_head global_link;
 	unsigned long start;		/* Start offset always 0 for dri2 */
 	size_t total;		/* size addr space maps (ex. 2GB for ggtt) */
 
@@ -1120,6 +1121,7 @@ typedef struct drm_i915_private {
 	enum modeset_restore modeset_restore;
 	struct mutex modeset_restore_lock;
 
+	struct list_head vm_list; /* Global list of all address spaces */
 	struct i915_gtt gtt; /* VMA representing the global address space */
 
 	struct i915_gem_mm mm;