ARM: fix booting low-vectors machines

Commit f6f91b0d9fd9 (ARM: allow kuser helpers to be removed from the
vector page) required two pages for the vectors code.  Although the
code setting up the initial page tables was updated, the code which
allocates page tables for new processes wasn't, neither was the code
which tears down the mappings.  Fix this.

Fixes: f6f91b0d9fd9 ("ARM: allow kuser helpers to be removed from the vector page")
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: <stable@vger.kernel.org>

arch/arm/include/asm/pgtable.h

@@ -61,7 +61,7 @@ extern void __pgd_error(const char *file, int line, pgd_t);
  * mapping to be mapped at.  This is particularly important for
  * non-high vector CPUs.
  */
-#define FIRST_USER_ADDRESS	PAGE_SIZE
+#define FIRST_USER_ADDRESS	(PAGE_SIZE * 2)
 
 /*
  * Use TASK_SIZE as the ceiling argument for free_pgtables() and

arch/arm/mm/mmap.c

@@ -146,7 +146,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;
-	info.low_limit = PAGE_SIZE;
+	info.low_limit = FIRST_USER_ADDRESS;
 	info.high_limit = mm->mmap_base;
 	info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;

arch/arm/mm/pgd.c

@@ -87,7 +87,8 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 		init_pud = pud_offset(init_pgd, 0);
 		init_pmd = pmd_offset(init_pud, 0);
 		init_pte = pte_offset_map(init_pmd, 0);
-		set_pte_ext(new_pte, *init_pte, 0);
+		set_pte_ext(new_pte + 0, init_pte[0], 0);
+		set_pte_ext(new_pte + 1, init_pte[1], 0);
 		pte_unmap(init_pte);
 		pte_unmap(new_pte);
 	}