parisc: fix usage of 32bit PTE page table entries on 32bit kernels

This patch fixes a long outstanding bug on 32bit parisc linux kernels
which prevented us from using 32bit PTE table entries (instead of 64bit
entries of which 32bit were unused).

The problem was caused by this assembler statement in the L2_ptep
macro in arch/parisc/kernel/entry.S:447:
	EXTR \va,31-ASM_PGDIR_SHIFT,ASM_BITS_PER_PGD,\index
which expanded to
	extrw,u r8,9,11,r1
and which has undefined behavior since the length value (11) extends
beyond the leftmost bit (11-1 > 9).
Interestingly PA2.0 processors seem to don't care and just zero-extend
the value, while PA1.1 processors don't.

Fix this problem by detecting an address space overflow with ASM_BITS_PER_PGD
and adjusting it accordingly. To prevent such problems in the future,
some compile time sanity checks in arch/parisc/mm/init.c were added.

Since the page table now only consumes half of it's old size, we can
use the freed memory to harmonize 32- and 64bit kernels and let both
map 16MB for the initial page table.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>

1 files changed, 10 insertions, 5 deletions

diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index 470a4b88124d..a27d2e200fb2 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -50,11 +50,7 @@
         printk("%s:%d: bad pgd %08lx.\n", __FILE__, __LINE__, (unsigned long)pgd_val(e))
 
 /* This is the size of the initially mapped kernel memory */
-#ifdef CONFIG_64BIT
 #define KERNEL_INITIAL_ORDER    24      /* 0 to 1<<24 = 16MB */
-#else
-#define KERNEL_INITIAL_ORDER    23      /* 0 to 1<<23 = 8MB */
-#endif
 #define KERNEL_INITIAL_SIZE     (1 << KERNEL_INITIAL_ORDER)
 
 #if defined(CONFIG_64BIT) && defined(CONFIG_PARISC_PAGE_SIZE_4KB)
@@ -91,16 +87,25 @@
 
 /* Definitions for 1st level */
 #define PGDIR_SHIFT     (PMD_SHIFT + BITS_PER_PMD)
+#if (PGDIR_SHIFT + PAGE_SHIFT + PGD_ORDER - BITS_PER_PGD_ENTRY) > BITS_PER_LONG
+#define BITS_PER_PGD    (BITS_PER_LONG - PGDIR_SHIFT)
+#else
 #define BITS_PER_PGD    (PAGE_SHIFT + PGD_ORDER - BITS_PER_PGD_ENTRY)
+#endif
 #define PGDIR_SIZE      (1UL << PGDIR_SHIFT)
 #define PGDIR_MASK      (~(PGDIR_SIZE-1))
 #define PTRS_PER_PGD    (1UL << BITS_PER_PGD)
 #define USER_PTRS_PER_PGD       PTRS_PER_PGD
 
+#ifdef CONFIG_64BIT
 #define MAX_ADDRBITS    (PGDIR_SHIFT + BITS_PER_PGD)
 #define MAX_ADDRESS     (1UL << MAX_ADDRBITS)
-
 #define SPACEID_SHIFT   (MAX_ADDRBITS - 32)
+#else
+#define MAX_ADDRBITS    (BITS_PER_LONG)
+#define MAX_ADDRESS     (1UL << MAX_ADDRBITS)
+#define SPACEID_SHIFT   0
+#endif
 
 /* This calculates the number of initial pages we need for the initial
  * page tables */