sh: Fix fatal oops in copy_user_page() on sh4a (SH7780).

We had a pretty interesting oops happening, where copy_user_page()
was down()'ing p3map_sem[] with a bogus offset (particularly, an
offset that hadn't been initialized with sema_init(), due to the
mismatch between cpu_data->dcache.n_aliases and what was assumed
based off of the old CACHE_ALIAS value).

Luckily, spinlock debugging caught this for us, and so we drop
the old hardcoded CACHE_ALIAS for sh4 completely and rely on the
run-time probed cpu_data->dcache.alias_mask. This in turn gets
the p3map_sem[] index right, and everything works again.

While we're at it, also convert to 4-level page tables..
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/pg-sh4.c

@@ -2,7 +2,7 @@
  * arch/sh/mm/pg-sh4.c
  *
  * Copyright (C) 1999, 2000, 2002  Niibe Yutaka
- * Copyright (C) 2002  Paul Mundt
+ * Copyright (C) 2002 - 2005  Paul Mundt
  *
  * Released under the terms of the GNU GPL v2.0.
  */
@@ -23,6 +23,8 @@
 
 extern struct semaphore p3map_sem[];
 
+#define CACHE_ALIAS (cpu_data->dcache.alias_mask)
+
 /*
  * clear_user_page
  * @to: P1 address
@@ -41,8 +43,9 @@ void clear_user_page(void *to, unsigned long address, struct page *page)
 					   _PAGE_HW_SHARED | _PAGE_FLAGS_HARD);
 		unsigned long phys_addr = PHYSADDR(to);
 		unsigned long p3_addr = P3SEG + (address & CACHE_ALIAS);
-		pgd_t *dir = pgd_offset_k(p3_addr);
-		pmd_t *pmd = pmd_offset(dir, p3_addr);
+		pgd_t *pgd = pgd_offset_k(p3_addr);
+		pud_t *pud = pud_offset(pgd, p3_addr);
+		pmd_t *pmd = pmd_offset(pud, p3_addr);
 		pte_t *pte = pte_offset_kernel(pmd, p3_addr);
 		pte_t entry;
 		unsigned long flags;
@@ -80,8 +83,9 @@ void copy_user_page(void *to, void *from, unsigned long address,
 					   _PAGE_HW_SHARED | _PAGE_FLAGS_HARD);
 		unsigned long phys_addr = PHYSADDR(to);
 		unsigned long p3_addr = P3SEG + (address & CACHE_ALIAS);
-		pgd_t *dir = pgd_offset_k(p3_addr);
-		pmd_t *pmd = pmd_offset(dir, p3_addr);
+		pgd_t *pgd = pgd_offset_k(p3_addr);
+		pud_t *pud = pud_offset(pgd, p3_addr);
+		pmd_t *pmd = pmd_offset(pud, p3_addr);
 		pte_t *pte = pte_offset_kernel(pmd, p3_addr);
 		pte_t entry;
 		unsigned long flags;

include/asm-sh/cpu-sh4/cacheflush.h

@@ -16,10 +16,6 @@
  *  caching; in which case they're only semi-broken),
  *  so we need them.
  */
-
-/* Page is 4K, OC size is 16K, there are four lines. */
-#define CACHE_ALIAS 0x00003000
-
 struct page;
 struct mm_struct;
 struct vm_area_struct;