x86: fix early_ioremap()/btmap

fix a long-standing weakness of the early-ioremap allocator: it
uses a single pgd entry for the boot mappings, and was not properly
protecting itself against crossing a 2MB (4MB) boundary.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/asm-x86/fixmap_32.h b/include/asm-x86/fixmap_32.h
index 46bedb7b5426..fde140fd6d95 100644
--- a/include/asm-x86/fixmap_32.h
+++ b/include/asm-x86/fixmap_32.h
@@ -90,10 +90,18 @@ enum fixed_addresses {
         FIX_PARAVIRT_BOOTMAP,
 #endif
         __end_of_permanent_fixed_addresses,
-        /* temporary boot-time mappings, used before ioremap() is functional */
+        /*
+         * 256 temporary boot-time mappings, used by early_ioremap(),
+         * before ioremap() is functional.
+         *
+         * We round it up to the next 512 pages boundary so that we
+         * can have a single pgd entry and a single pte table:
+         */
 #define NR_FIX_BTMAPS           64
 #define FIX_BTMAPS_NESTING      4
-        FIX_BTMAP_END = __end_of_permanent_fixed_addresses,
+        FIX_BTMAP_END =
+                __end_of_permanent_fixed_addresses + 512 -
+                        (__end_of_permanent_fixed_addresses & 511),
         FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_NESTING - 1,
         FIX_WP_TEST,
         __end_of_fixed_addresses