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    Subject[PATCH] BUG in pv_clock when overflow condition is detected
    Date
    BUG when overflow occurs at pvclock.c:pvclock_get_nsec_offset

    u64 delta = native_read_tsc() - shadow->tsc_timestamp;

    this might happen at an attempt to read an uninitialized yet clock.
    It won't prevent stalls and hangs but at least it won't do it silently.

    Signed-off-by: Igor Mammedov <imammedo@redhat.com>
    ---
    arch/x86/kernel/pvclock.c | 5 ++++-
    1 files changed, 4 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
    index 42eb330..35a6190 100644
    --- a/arch/x86/kernel/pvclock.c
    +++ b/arch/x86/kernel/pvclock.c
    @@ -43,7 +43,10 @@ void pvclock_set_flags(u8 flags)

    static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
    {
    - u64 delta = native_read_tsc() - shadow->tsc_timestamp;
    + u64 delta;
    + u64 tsc = native_read_tsc();
    + BUG_ON(tsc < shadow->tsc_timestamp);
    + delta = tsc - shadow->tsc_timestamp;
    return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
    shadow->tsc_shift);
    }
    --
    1.7.7.6


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