drm: Don't leak phys_wc "handles" to userspace

I didn't fix this in the earlier patch -- it would have broken the
build due to the now-deleted garbage in drm_os_linux.h.

Reviewed-by: Daniel Vetter <[e-mail]>
Signed-off-by: Andy Lutomirski <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/drm_bufs.c

···
 
 	/* avoid a warning on 64-bit, this casting isn't very nice, but the API is set so too late */
 	map->handle = (void *)(unsigned long)maplist->user_token;
+
+	/*
+	 * It appears that there are no users of this value whatsoever --
+	 * drmAddMap just discards it.  Let's not encourage its use.
+	 * (Keeping drm_addmap_core's returned mtrr value would be wrong --
+	 *  it's not a real mtrr index anymore.)
+	 */
+	map->mtrr = -1;
+
 	return 0;
 }
 

drivers/gpu/drm/drm_ioctl.c

···
 
 #include <linux/pci.h>
 #include <linux/export.h>
+#ifdef CONFIG_X86
+#include <asm/mtrr.h>
+#endif
 
 /**
  * Get the bus id.
···
 	map->type = r_list->map->type;
 	map->flags = r_list->map->flags;
 	map->handle = (void *)(unsigned long) r_list->user_token;
-	map->mtrr = r_list->map->mtrr;
+
+#ifdef CONFIG_X86
+	/*
+	 * There appears to be exactly one user of the mtrr index: dritest.
+	 * It's easy enough to keep it working on non-PAT systems.
+	 */
+	map->mtrr = phys_wc_to_mtrr_index(r_list->map->mtrr);
+#else
+	map->mtrr = -1;
+#endif
+
 	mutex_unlock(&dev->struct_mutex);
 
 	return 0;