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.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 597ac155c91c..6ef98c55a899 100644
--- a/arch/x86/mm/ioremap.c
+++ b/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));