drm/i915/gem: Drop local vma->vm_file reference

We use the global device inode, shared amongst all files, and not the
user's device filp to provide the backing storage for the mmap. The
vma->vm_file provides a redundant reference that breaks existing
expected behaviour that closing the user's device fd will release the
resources bound to it, if a mmap persists. (Even without the
vma->vm_file, the mmap will persist past the user's fd as the storage is
bound to the device, i.e. our reference is on the object not file.)

Fixes: cc662126b413 ("drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/919
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200101141007.755429-1-chris@chris-wilson.co.uk

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2c7e3020e766..2ee9f57d165d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1252,6 +1252,16 @@ struct drm_i915_private {
 			struct llist_head free_list;
 			struct work_struct free_work;
 		} contexts;
+
+		/*
+		 * We replace the local file with a global mappings as the
+		 * backing storage for the mmap is on the device and not
+		 * on the struct file, and we do not want to prolong the
+		 * lifetime of the local fd. To minimise the number of
+		 * anonymous inodes we create, we use a global singleton to
+		 * share the global mapping.
+		 */
+		struct file *mmap_singleton;
 	} gem;
 
 	u8 pch_ssc_use;