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    Subject[PATCH 4.4 31/68] pvclock: Add CPU barriers to get correct version value
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Minfei Huang <mnghuan@gmail.com>

    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>

    ---
    arch/x86/include/asm/pvclock.h | 2 ++
    arch/x86/kernel/pvclock.c | 4 ++++
    2 files changed, 6 insertions(+)

    --- a/arch/x86/include/asm/pvclock.h
    +++ b/arch/x86/include/asm/pvclock.h
    @@ -76,6 +76,8 @@ unsigned __pvclock_read_cycles(const str
    u8 ret_flags;

    version = src->version;
    + /* Make the latest version visible */
    + smp_rmb();

    offset = pvclock_get_nsec_offset(src);
    ret = src->system_time + offset;
    --- a/arch/x86/kernel/pvclock.c
    +++ b/arch/x86/kernel/pvclock.c
    @@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcp

    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

    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)) {

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