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    Subject[PATCH 060/105] x86: kvmclock: zero initialize pvclock shared memory area
    Date
    3.8.13.4 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Igor Mammedov <imammedo@redhat.com>

    commit 07868fc6aaf57847b0f3a3d53086b7556eb83f4a upstream.

    kernel might hung in pvclock_clocksource_read() due to
    uninitialized memory might contain odd version value in
    following cycle:

    do {
    version = __pvclock_read_cycles(src, &ret, &flags);
    } while ((src->version & 1) || version != src->version);

    if secondary kvmclock is accessed before it's registered with kvm.

    Clear garbage in pvclock shared memory area right after it's
    allocated to avoid this issue.

    Ref: https://bugzilla.kernel.org/show_bug.cgi?id=59521
    Signed-off-by: Igor Mammedov <imammedo@redhat.com>
    [See BZ for analysis. We may want a different fix for 3.11, but
    this is the safest for now - Paolo]
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    arch/x86/kernel/kvmclock.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
    index 5bedbdd..a855a2e 100644
    --- a/arch/x86/kernel/kvmclock.c
    +++ b/arch/x86/kernel/kvmclock.c
    @@ -238,6 +238,7 @@ void __init kvmclock_init(void)
    if (!mem)
    return;
    hv_clock = __va(mem);
    + memset(hv_clock, 0, size);

    if (kvm_register_clock("boot clock")) {
    hv_clock = NULL;
    --
    1.8.1.2


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