linux-kernel - [RFC 14/20] timens: Add align for timens

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Message-Id: <20180919205037.9574-15-dima@arista.com>
Date:   Wed, 19 Sep 2018 21:50:31 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org
Subject: [RFC 14/20] timens: Add align for timens_offsets

Align offsets so that Time Namespace will work for ia32 applications on
x86_64 host.

Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 include/linux/timens_offsets.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/timens_offsets.h b/include/linux/timens_offsets.h
index 777530c46852..92a8ea5601eb 100644
--- a/include/linux/timens_offsets.h
+++ b/include/linux/timens_offsets.h
@@ -2,9 +2,16 @@
 #ifndef _LINUX_TIME_OFFSETS_H
 #define _LINUX_TIME_OFFSETS_H
 
+/*
+ * Time offsets need align as they're placed on vvar page,
+ * which should have tail paddings on ia32 vdso.
+ * Otherwise as u64 has align(4), vvar offsets will differ.
+ * On 64-bit big-endian systems vdso should convert to timespec64
+ * to timespec because of a padding occuring between the fields.
+ */
 struct timens_offsets {
-	struct timespec64  monotonic_time_offset;
-	struct timespec64  monotonic_boottime_offset;
+	struct timespec64  monotonic_time_offset __aligned(8);
+	struct timespec64  monotonic_boottime_offset __aligned(8);
 };
 
 #endif
-- 
2.13.6