drm/i915/gem: Adjust vma offset for framebuffer mmap offset

When mapping a framebuffer object, the virtual memory area (VMA)
offset ('vm_pgoff') should be adjusted by the start of the
'vma_node' associated with the object. This ensures that the VMA
offset is correctly aligned with the corresponding offset within
the GGTT aperture.

Increment vm_pgoff by the start of the vma_node with the offset=
provided by the user.

Suggested-by: Chris Wilson <[email protected]>
Signed-off-by: Andi Shyti <[email protected]>
Reviewed-by: Jonathan Cavitt <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Cc: <[email protected]> # v4.9+
[Joonas: Add Cc: stable]
Signed-off-by: Joonas Lahtinen <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 60a2066)
Signed-off-by: Joonas Lahtinen <[email protected]>

Author: Andi Shyti

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -1084,6 +1084,8 @@ int i915_gem_fb_mmap(struct drm_i915_gem_object *obj, struct vm_area_struct *vma
 		mmo = mmap_offset_attach(obj, mmap_type, NULL);
 		if (IS_ERR(mmo))
 			return PTR_ERR(mmo);
+
+		vma->vm_pgoff += drm_vma_node_start(&mmo->vma_node);
 	}
 
 	/*