From 749d088b8e7f4b9826ede02b9a043e417fa84aa1 Mon Sep 17 00:00:00 2001 From: Minfei Huang 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 Signed-off-by: Paolo Bonzini --- 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 fdcc040..538ae94 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 99bfc02..7f82fe0 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)) { -- 2.7.4