x86/mm: Only add extra pages count for the first memory range during pre-allocation...

Robin found this regression:

| I just tried to boot an 8TB system.  It fails very early in boot with:
| Kernel panic - not syncing: Cannot find space for the kernel page tables

git bisect commit 4c94dab537bcc86ad95f4be935083fe416c79df6.

A git revert of that commit does boot past that point on the 8TB
configuration.

That commit will add up extra pages for all memory range even
above 4g.

Try to limit that extra page count adding to first entry only.

Bisected-by: Robin Holt <holt@sgi.com>
Tested-by: Robin Holt <holt@sgi.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/CAE9FiQUj3wyzQxtq9yzBNc9u220p8JZ1FYHG7t%3DMOzJ%3D9BZMYA@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 97141c26a13ac8400cfce07c36d55cca50962b26..bc4e9d84157fc0c9aa85e71837998da166c1fa57 100644 (file)
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -62,7 +62,8 @@ static void __init find_early_table_space(struct map_range *mr, unsigned long en
                extra += PMD_SIZE;
 #endif
                /* The first 2/4M doesn't use large pages. */
-               extra += mr->end - mr->start;
+               if (mr->start < PMD_SIZE)
+                       extra += mr->end - mr->start;
 
                ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
        } else