MIPS: Limit fixrange_init() to the FIXMAP region

fixrange_init() allocates page tables for all addresses higher than
FIXADDR_TOP.  On processors that override the default FIXADDR_TOP
address of 0xfffe_0000, this can consume up to 4 pages (1 page per 4MB)
for pgd's that are never used.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1980/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/init.c

@@ -277,11 +277,11 @@ void __init fixrange_init(unsigned long start, unsigned long end,
 	k = __pmd_offset(vaddr);
 	pgd = pgd_base + i;
 
-	for ( ; (i < PTRS_PER_PGD) && (vaddr != end); pgd++, i++) {
+	for ( ; (i < PTRS_PER_PGD) && (vaddr < end); pgd++, i++) {
 		pud = (pud_t *)pgd;
-		for ( ; (j < PTRS_PER_PUD) && (vaddr != end); pud++, j++) {
+		for ( ; (j < PTRS_PER_PUD) && (vaddr < end); pud++, j++) {
 			pmd = (pmd_t *)pud;
-			for (; (k < PTRS_PER_PMD) && (vaddr != end); pmd++, k++) {
+			for (; (k < PTRS_PER_PMD) && (vaddr < end); pmd++, k++) {
 				if (pmd_none(*pmd)) {
 					pte = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
 					set_pmd(pmd, __pmd((unsigned long)pte));

arch/mips/mm/pgtable-32.c

@@ -52,7 +52,7 @@ void __init pagetable_init(void)
 	 * Fixed mappings:
 	 */
 	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
-	fixrange_init(vaddr, 0, pgd_base);
+	fixrange_init(vaddr, vaddr + FIXADDR_SIZE, pgd_base);
 
 #ifdef CONFIG_HIGHMEM
 	/*

arch/mips/mm/pgtable-64.c

@@ -76,5 +76,5 @@ void __init pagetable_init(void)
 	 * Fixed mappings:
 	 */
 	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
-	fixrange_init(vaddr, 0, pgd_base);
+	fixrange_init(vaddr, vaddr + FIXADDR_SIZE, pgd_base);
 }