memremap: fix highmem support

Currently memremap checks if the range is "System RAM" and returns the kernel linear address. This is broken for highmem platforms where a range may be "System RAM", but is not part of the kernel linear mapping. Fallback to ioremap_cache() in these cases, to let the arch code attempt to handle it. Note that ARM ioremap will WARN when attempting to remap ram, and in that case the caller needs to be fixed. For this reason, existing ioremap_cache() usages for ARM are already trained to avoid attempts to remap ram. The impact of this bug is low for now since the pmem driver is the only user of memremap(), but this is important to fix before more conversions to memremap arrive in 4.4.

Dan Williams committed 11 years ago

Commit 182475b1 parent 25cb62b1 file · +12 −2Browse files

Unified · Split

kernel/memremap.c+12−2

 }
 #endif
+static void *try_ram_remap(resource_size_t offset, size_t size)
+{
+	struct page *page = pfn_to_page(offset >> PAGE_SHIFT);
+	/* In the simple case just return the existing linear address */
+	if (!PageHighMem(page))
+		return __va(offset);
+	return NULL; /* fallback to ioremap_cache */
+}
 /**
  * memremap() - remap an iomem_resource as cacheable memory
  * @offset: iomem resource start address
 		 * the requested range is potentially in "System RAM"
 		 */
 		if (is_ram == REGION_INTERSECTS)
-			addr = __va(offset);
+			addr = try_ram_remap(offset, size);
-		else
+		if (!addr)
 			addr = ioremap_cache(offset, size);
 	}