x86, mm: Ensure correct alignment of the fixmap

The early_ioremap code requires that its buffers not span a PMD
boundary.  The logic for ensuring that only works if the fixmap is
aligned, so assert that it's aligned correctly.

To make this work reliably, reserve_top_address needs to be
adjusted.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/e59a5f4362661f75dd4841fa74e1f2448045e245.1399317206.git.luto@amacapital.netSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/mm/ioremap.c

@@ -355,6 +355,12 @@ void __init early_ioremap_init(void)
 {
 	pmd_t *pmd;
 
+#ifdef CONFIG_X86_64
+	BUILD_BUG_ON((fix_to_virt(0) + PAGE_SIZE) & ((1 << PMD_SHIFT) - 1));
+#else
+	WARN_ON((fix_to_virt(0) + PAGE_SIZE) & ((1 << PMD_SHIFT) - 1));
+#endif
+
 	early_ioremap_setup();
 
 	pmd = early_ioremap_pmd(fix_to_virt(FIX_BTMAP_BEGIN));

arch/x86/mm/pgtable.c

@@ -449,9 +449,9 @@ void __init reserve_top_address(unsigned long reserve)
 {
 #ifdef CONFIG_X86_32
 	BUG_ON(fixmaps_set > 0);
-	printk(KERN_INFO "Reserving virtual address space above 0x%08x\n",
-	       (int)-reserve);
-	__FIXADDR_TOP = -reserve - PAGE_SIZE;
+	__FIXADDR_TOP = round_down(-reserve, 1 << PMD_SHIFT) - PAGE_SIZE;
+	printk(KERN_INFO "Reserving virtual address space above 0x%08lx (rounded to 0x%08lx)\n",
+	       -reserve, __FIXADDR_TOP + PAGE_SIZE);
 #endif
 }