pvclock: Add CPU barriers to get correct version value

commit 749d088b8e7f4b9826ede02b9a043e417fa84aa1 upstream.

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
Signed-off-by: Minfei Huang <mnghuan@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 7a6bed5c08bc3cc266dcc7c24e71863f684d2630..baad72e4c1000d0387ca076c57a9645bcbbf189d 100644 (file)
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -76,6 +76,8 @@ 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 2f355d229a587771680b28080d92fd06f345d7e7..bf0ce75735b02f0c5cbfb6b9ae5e616b512a271f 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)) {