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: ebdaf7cd8697e43d401daa7af6321ce7c8d564c7
Cc: stable@vger.kernel.org
Signed-off-by: Minfei Huang <mnghuan@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index fdcc04020636e33269d7a756162cfe852f509823..538ae944855e7d28870a4d430a83797a03446579 100644 (file)
--- 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 99bfc025111d3dd62bc7c1753d126e97fb4e48ac..7f82fe0a6807cc0be8d782f5a7e8d6a6e3384ab5 100644 (file)
--- 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)) {