drm/i915: Keep refs on the object over the lifetime of vmas for GTT mmap.

This fixes potential fault at fault time if the object was unreferenced
while the mapping still existed.  Now, while the mmap_offset only lives
for the lifetime of the object, the object also stays alive while a vma
exists that needs it.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 5dad6b9d0dec..88d3368ffddd 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -463,6 +463,26 @@ drm_gem_object_handle_free(struct kref *kref)
 }
 EXPORT_SYMBOL(drm_gem_object_handle_free);
 
+void drm_gem_vm_open(struct vm_area_struct *vma)
+{
+        struct drm_gem_object *obj = vma->vm_private_data;
+
+        drm_gem_object_reference(obj);
+}
+EXPORT_SYMBOL(drm_gem_vm_open);
+
+void drm_gem_vm_close(struct vm_area_struct *vma)
+{
+        struct drm_gem_object *obj = vma->vm_private_data;
+        struct drm_device *dev = obj->dev;
+
+        mutex_lock(&dev->struct_mutex);
+        drm_gem_object_unreference(obj);
+        mutex_unlock(&dev->struct_mutex);
+}
+EXPORT_SYMBOL(drm_gem_vm_close);
+
+
 /**
  * drm_gem_mmap - memory map routine for GEM objects
  * @filp: DRM file pointer
@@ -524,6 +544,14 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
 #endif
         vma->vm_page_prot = __pgprot(prot);
 
+        /* Take a ref for this mapping of the object, so that the fault
+         * handler can dereference the mmap offset's pointer to the object.
+         * This reference is cleaned up by the corresponding vm_close
+         * (which should happen whether the vma was created by this call, or
+         * by a vm_open due to mremap or partial unmap or whatever).
+         */
+        drm_gem_object_reference(obj);
+
         vma->vm_file = filp;    /* Needed for drm_vm_open() */
         drm_vm_open_locked(vma);