[tip:x86/urgent] x86/mm: Make split_page_count check for empty levels

[tip-bot for Dave Jones <tipbot@zytor.com>]

Commit-ID:  3f1ac1cdc4fdf894e35c0e4fd103b54eec8a28c0
Gitweb:     http://git.kernel.org/tip/3f1ac1cdc4fdf894e35c0e4fd103b54eec8a28c0
Author:     Dave Jones <davej@codemonkey.org.uk>
AuthorDate: Mon, 11 Jan 2016 12:04:28 -0500
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 12 Jan 2016 11:04:53 +0100

x86/mm: Make split_page_count check for empty levels

In PAGEALLOC_DEBUG builds, we disable the 2M pages. Unfortunatly when we
split up mappings during boot, split_page_count doesn't take this into
account, and starts decrementing an empty direct_pages_count level.

This results in /proc/meminfo showing crazy things like
DirectMap2M:    18446744073709543424 kB

Signed-off-by: Dave Jones <davej@codemonkey.org.uk>
Link: http://lkml.kernel.org/r/20160111170428.GA8547@codemonkey.org.uk
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/mm/pageattr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index a3137a4..ff0e0c6 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -66,6 +66,9 @@ void update_page_count(int level, unsigned long pages)
 
 static void split_page_count(int level)
 {
+	if (direct_pages_count[level] == 0)
+		return;
+
 	direct_pages_count[level]--;
 	direct_pages_count[level - 1] += PTRS_PER_PTE;
 }