powerpc/mm: Add option for non-atomic PTE updates to ppc64

ppc32 has it already, add it to ppc64 as a preliminary for adding
support for Book3E 64-bit support

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/pgtable-ppc64.h

@@ -178,6 +178,7 @@ static inline unsigned long pte_update(struct mm_struct *mm,
 				       pte_t *ptep, unsigned long clr,
 				       int huge)
 {
+#ifdef PTE_ATOMIC_UPDATES
 	unsigned long old, tmp;
 
 	__asm__ __volatile__(
@@ -190,7 +191,10 @@ static inline unsigned long pte_update(struct mm_struct *mm,
 	: "=&r" (old), "=&r" (tmp), "=m" (*ptep)
 	: "r" (ptep), "r" (clr), "m" (*ptep), "i" (_PAGE_BUSY)
 	: "cc" );
-
+#else
+	unsigned long old = pte_val(*ptep);
+	*ptep = __pte(old & ~clr);
+#endif
 	/* huge pages use the old page table lock */
 	if (!huge)
 		assert_pte_locked(mm, addr);
@@ -278,6 +282,8 @@ static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
 	unsigned long bits = pte_val(entry) &
 		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW |
 		 _PAGE_EXEC | _PAGE_HWEXEC);
+
+#ifdef PTE_ATOMIC_UPDATES
 	unsigned long old, tmp;
 
 	__asm__ __volatile__(
@@ -290,6 +296,10 @@ static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
 	:"=&r" (old), "=&r" (tmp), "=m" (*ptep)
 	:"r" (bits), "r" (ptep), "m" (*ptep), "i" (_PAGE_BUSY)
 	:"cc");
+#else
+	unsigned long old = pte_val(*ptep);
+	*ptep = __pte(old | bits);
+#endif
 }
 
 #define __HAVE_ARCH_PTE_SAME

arch/powerpc/include/asm/pte-hash64.h

@@ -41,6 +41,8 @@
 #define _PTEIDX_SECONDARY	0x8
 #define _PTEIDX_GROUP_IX	0x7
 
+/* Hash table based platforms need atomic updates of the linux PTE */
+#define PTE_ATOMIC_UPDATES	1
 
 #ifdef CONFIG_PPC_64K_PAGES
 #include <asm/pte-hash64-64k.h>