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    SubjectRe: [PATCH] BUG in pv_clock when overflow condition is detected
    On 02/13/2012 08:20 PM, Igor Mammedov wrote:
    > 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);

    Maybe a WARN_ON_ONCE()? Otherwise a relatively minor hypervisor bug can
    kill the guest.

    --
    error compiling committee.c: too many arguments to function



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