powerpc/mm: enable the use of page table cache of order 0

hugepages uses a cache of order 0. Lets allow page tables
of order 0 in the common part in order to avoid open coding
in hugetlb
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/book3s/32/pgalloc.h

@@ -25,10 +25,7 @@
 extern void __bad_pte(pmd_t *pmd);
 
 extern struct kmem_cache *pgtable_cache[];
-#define PGT_CACHE(shift) ({				\
-			BUG_ON(!(shift));		\
-			pgtable_cache[(shift) - 1];	\
-		})
+#define PGT_CACHE(shift) pgtable_cache[shift]
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {

arch/powerpc/include/asm/book3s/64/pgalloc.h

@@ -37,10 +37,7 @@ extern struct vmemmap_backing *vmemmap_list;
 #define MAX_PGTABLE_INDEX_SIZE	0xf
 
 extern struct kmem_cache *pgtable_cache[];
-#define PGT_CACHE(shift) ({				\
-			BUG_ON(!(shift));		\
-			pgtable_cache[(shift) - 1];	\
-		})
+#define PGT_CACHE(shift) pgtable_cache[shift]
 
 extern pte_t *pte_fragment_alloc(struct mm_struct *, unsigned long, int);
 extern pmd_t *pmd_fragment_alloc(struct mm_struct *, unsigned long);

arch/powerpc/include/asm/nohash/32/pgalloc.h

@@ -25,10 +25,7 @@
 extern void __bad_pte(pmd_t *pmd);
 
 extern struct kmem_cache *pgtable_cache[];
-#define PGT_CACHE(shift) ({				\
-			BUG_ON(!(shift));		\
-			pgtable_cache[(shift) - 1];	\
-		})
+#define PGT_CACHE(shift) pgtable_cache[shift]
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {

arch/powerpc/include/asm/nohash/64/pgalloc.h

@@ -36,10 +36,7 @@ extern struct vmemmap_backing *vmemmap_list;
 #define MAX_PGTABLE_INDEX_SIZE	0xf
 
 extern struct kmem_cache *pgtable_cache[];
-#define PGT_CACHE(shift) ({				\
-			BUG_ON(!(shift));		\
-			pgtable_cache[(shift) - 1];	\
-		})
+#define PGT_CACHE(shift) pgtable_cache[shift]
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {

arch/powerpc/mm/init-common.c

@@ -40,7 +40,7 @@ static void pmd_ctor(void *addr)
 	memset(addr, 0, PMD_TABLE_SIZE);
 }
 
-struct kmem_cache *pgtable_cache[MAX_PGTABLE_INDEX_SIZE];
+struct kmem_cache *pgtable_cache[MAX_PGTABLE_INDEX_SIZE + 1];
 EXPORT_SYMBOL_GPL(pgtable_cache);	/* used by kvm_hv module */
 
 /*
@@ -71,7 +71,7 @@ void pgtable_cache_add(unsigned shift, void (*ctor)(void *))
 	 * moment, gcc doesn't seem to recognize is_power_of_2 as a
 	 * constant expression, so so much for that. */
 	BUG_ON(!is_power_of_2(minalign));
-	BUG_ON((shift < 1) || (shift > MAX_PGTABLE_INDEX_SIZE));
+	BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
 
 	if (PGT_CACHE(shift))
 		return; /* Already have a cache of this size */
@@ -83,7 +83,7 @@ void pgtable_cache_add(unsigned shift, void (*ctor)(void *))
 		panic("Could not allocate pgtable cache for order %d", shift);
 
 	kfree(name);
-	pgtable_cache[shift - 1] = new;
+	pgtable_cache[shift] = new;
 
 	pr_debug("Allocated pgtable cache for order %d\n", shift);
 }