From: Roman Kagan <rkagan@virtuozzo.com>
To: <linux-kernel@vger.kernel.org>
Cc: "Denis V. Lunev" <den@openvz.org>,
Roman Kagan <rkagan@virtuozzo.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
<x86@kernel.org>, Andy Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@suse.de>, Paolo Bonzini <pbonzini@redhat.com>,
<stable@vger.kernel.org>
Subject: [PATCH] x86:pvclock: add missing barriers
Date: Wed, 8 Jun 2016 21:11:39 +0300 [thread overview]
Message-ID: <1465409499-23166-1-git-send-email-rkagan@virtuozzo.com> (raw)
Gradual removal of excessive barriers in pvclock reading functions
(commits 502dfeff239e8313bfbe906ca0a1a6827ac8481b,
a3eb97bd80134ba07864ca00747466c02118aca1) ended up removing too much:
although rdtsc is now orderd WRT other loads, there's no protection
against the compiler reordering the loads of ->version with the loads of
other fields.
E.g. on my system gcc-5.3.1 generates code which loads ->system_time and
->flags outside of the ->version test loop.
(Re)introduce the compiler barriers around accesses to the contents of
pvclock. While at this, make the function a bit more compact by
removing unnecessary local variables.
Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
---
arch/x86/include/asm/pvclock.h | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index fdcc040..65c4de2 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -80,18 +80,11 @@ static __always_inline
unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
cycle_t *cycles, u8 *flags)
{
- unsigned version;
- cycle_t ret, offset;
- u8 ret_flags;
-
- version = src->version;
-
- offset = pvclock_get_nsec_offset(src);
- ret = src->system_time + offset;
- ret_flags = src->flags;
-
- *cycles = ret;
- *flags = ret_flags;
+ unsigned version = src->version;
+ barrier();
+ *cycles = src->system_time + pvclock_get_nsec_offset(src);
+ *flags = src->flags;
+ barrier();
return version;
}
--
2.5.5
next reply other threads:[~2016-06-08 19:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-08 18:11 Roman Kagan [this message]
2016-06-08 19:45 ` [PATCH] x86:pvclock: add missing barriers Borislav Petkov
2016-06-08 21:01 ` Roman Kagan
2016-06-09 10:29 ` Roman Kagan
2016-06-12 10:02 ` Minfei Huang
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