ARM: 7649/1: mm: mm->context.id fix for big-endian

Since the new ASID code in b5466f8728
("ARM: mm: remove IPI broadcasting on ASID rollover") was changed to
use 64bit operations it has broken the BE operation due to an issue
with the MM code accessing sub-fields of mm->context.id.

When running in BE mode we see the values in mm->context.id are stored
with the highest value first, so the LDR in the arch/arm/mm/proc-macros.S
reads the wrong part of this field. To resolve this, change the LDR in
the mmid macro to load from +4.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/context.c

@@ -34,6 +34,9 @@
  * The ASID is used to tag entries in the CPU caches and TLBs.
  * The context ID is used by debuggers and trace logic, and
  * should be unique within all running processes.
+ *
+ * In big endian operation, the two 32 bit words are swapped if accesed by
+ * non 64-bit operations.
  */
 #define ASID_FIRST_VERSION	(1ULL << ASID_BITS)
 #define NUM_USER_ASIDS		(ASID_FIRST_VERSION - 1)

arch/arm/mm/proc-macros.S

@@ -38,9 +38,14 @@
 
 /*
  * mmid - get context id from mm pointer (mm->context.id)
+ * note, this field is 64bit, so in big-endian the two words are swapped too.
  */
 	.macro	mmid, rd, rn
+#ifdef __ARMEB__
+	ldr	\rd, [\rn, #MM_CONTEXT_ID + 4 ]
+#else
 	ldr	\rd, [\rn, #MM_CONTEXT_ID]
+#endif
 	.endm
 
 /*