mm: Tighten x86 /dev/mem with zeroing reads

[pandora-kernel.git] / arch / x86 / mm / init.c

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 222f5b7..dba71b2 100644 (file)
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -318,21 +318,40 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
  * is valid. The argument is a physical page number.
  *
- *
- * On x86, access has to be given to the first megabyte of ram because that area
- * contains bios code and data regions used by X and dosemu and similar apps.
- * Access has to be given to non-kernel-ram areas as well, these contain the PCI
- * mmio resources as well as potential bios/acpi data regions.
+ * On x86, access has to be given to the first megabyte of RAM because that
+ * area traditionally contains BIOS code and data regions used by X, dosemu,
+ * and similar apps. Since they map the entire memory range, the whole range
+ * must be allowed (for mapping), but any areas that would otherwise be
+ * disallowed are flagged as being "zero filled" instead of rejected.
+ * Access has to be given to non-kernel-ram areas as well, these contain the
+ * PCI mmio resources as well as potential bios/acpi data regions.
  */
 int devmem_is_allowed(unsigned long pagenr)
 {
-       if (pagenr < 256)
-               return 1;
-       if (iomem_is_exclusive(pagenr << PAGE_SHIFT))
+       if (page_is_ram(pagenr)) {
+               /*
+                * For disallowed memory regions in the low 1MB range,
+                * request that the page be shown as all zeros.
+                */
+               if (pagenr < 256)
+                       return 2;
+
+               return 0;
+       }
+
+       /*
+        * This must follow RAM test, since System RAM is considered a
+        * restricted resource under CONFIG_STRICT_IOMEM.
+        */
+       if (iomem_is_exclusive(pagenr << PAGE_SHIFT)) {
+               /* Low 1MB bypasses iomem restrictions. */
+               if (pagenr < 256)
+                       return 1;
+
                return 0;
-       if (!page_is_ram(pagenr))
-               return 1;
-       return 0;
+       }
+
+       return 1;
 }
 
 void free_init_pages(char *what, unsigned long begin, unsigned long end)