linux-kernel - [PATCH] kdump: force page alignment for per-CPU crash notes.

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Message-Id: <1330536083-13098-1-git-send-email-surovegin@google.com>
Date:	Wed, 29 Feb 2012 09:21:23 -0800
From:	Eugene Surovegin <surovegin@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	Eugene Surovegin <surovegin@...gle.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	kexec-list <kexec@...ts.infradead.org>
Subject: [PATCH] kdump: force page alignment for per-CPU crash notes.

Per-CPU allocations are not guaranteed to be physically contiguous.
However, kdump kernel and user-space code assumes that per-CPU
memory, used for saving CPU registers on crash, is.
This can cause corrupted /proc/vmcore in some cases - the main
symptom being huge ELF note section.

Force page alignment for note_buf_t to ensure that this assumption holds.

Signed-off-by: Eugene Surovegin <surovegin@...gle.com>
CC: Eric Biederman <ebiederm@...ssion.com>
CC: Vivek Goyal <vgoyal@...hat.com>
CC: kexec-list <kexec@...ts.infradead.org>
---
 kernel/kexec.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 7b08867..e641b5c 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1232,8 +1232,13 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
 
 static int __init crash_notes_memory_init(void)
 {
-	/* Allocate memory for saving cpu registers. */
-	crash_notes = alloc_percpu(note_buf_t);
+	/* Allocate memory for saving cpu registers.
+	 * Force page alignment to avoid crossing physical page boundary -
+	 * kexec-tools and kernel /proc/vmcore handler assume these per-CPU
+	 * chunks are physically contiguous.
+	 */
+	crash_notes = (note_buf_t __percpu *)__alloc_percpu(sizeof(note_buf_t),
+							    PAGE_SIZE);
 	if (!crash_notes) {
 		printk("Kexec: Memory allocation for saving cpu register"
 		" states failed\n");
-- 
1.7.9.1

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