+static struct inode *iomem_inode;
+
+#ifdef CONFIG_IO_STRICT_DEVMEM
+static void revoke_iomem(struct resource *res)
+{
+ /* pairs with smp_store_release() in iomem_init_inode() */
+ struct inode *inode = smp_load_acquire(&iomem_inode);
+
+ /*
+ * Check that the initialization has completed. Losing the race
+ * is ok because it means drivers are claiming resources before
+ * the fs_initcall level of init and prevent iomem_get_mapping users
+ * from establishing mappings.
+ */
+ if (!inode)
+ return;
+
+ /*
+ * The expectation is that the driver has successfully marked
+ * the resource busy by this point, so devmem_is_allowed()
+ * should start returning false, however for performance this
+ * does not iterate the entire resource range.
+ */
+ if (devmem_is_allowed(PHYS_PFN(res->start)) &&
+ devmem_is_allowed(PHYS_PFN(res->end))) {
+ /*
+ * *cringe* iomem=relaxed says "go ahead, what's the
+ * worst that can happen?"
+ */
+ return;
+ }
+
+ unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
+}
+#else
+static void revoke_iomem(struct resource *res) {}
+#endif
+
+struct address_space *iomem_get_mapping(void)
+{
+ /*
+ * This function is only called from file open paths, hence guaranteed
+ * that fs_initcalls have completed and no need to check for NULL. But
+ * since revoke_iomem can be called before the initcall we still need
+ * the barrier to appease checkers.
+ */
+ return smp_load_acquire(&iomem_inode)->i_mapping;
+}
+