From 749d088b8e7f4b9826ede02b9a043e417fa84aa1 Mon Sep 17 00:00:00 2001
From: Minfei Huang <mnghuan@gmail.com>
Date: Fri, 27 May 2016 14:17:10 +0800
Subject: [PATCH] pvclock: Add CPU barriers to get correct version value
Protocol for the "version" fields is: hypervisor raises it (making it
uneven) before it starts updating the fields and raises it again (making
it even) when it is done. Thus the guest can make sure the time values
it got are consistent by checking the version before and after reading
them.
Add CPU barries after getting version value just like what function
vread_pvclock does, because all of callees in this function is inline.
Fixes: 502dfeff239e8313bfbe906ca0a1a6827ac8481b
Cc: stable@vger.kernel.org
Signed-off-by: Minfei Huang <mnghuan@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/pvclock.h | 2 ++
arch/x86/kernel/pvclock.c | 4 ++++
2 files changed, 6 insertions(+)
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index fdcc04020636e..538ae944855e7 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -85,6 +85,8 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
u8 ret_flags;
version = src->version;
+ /* Make the latest version visible */
+ smp_rmb();
offset = pvclock_get_nsec_offset(src);
ret = src->system_time + offset;
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 99bfc025111d3..7f82fe0a6807c 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
do {
version = __pvclock_read_cycles(src, &ret, &flags);
+ /* Make sure that the version double-check is last. */
+ smp_rmb();
} while ((src->version & 1) || version != src->version);
return flags & valid_flags;
@@ -80,6 +82,8 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
do {
version = __pvclock_read_cycles(src, &ret, &flags);
+ /* Make sure that the version double-check is last. */
+ smp_rmb();
} while ((src->version & 1) || version != src->version);
if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
--
2.30.2