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    Subject[KVM timekeeping 10/35] Fix deep C-state TSC desynchronization
    Date
    When CPUs with unstable TSCs enter deep C-state, TSC may stop
    running. This causes us to require resynchronization. Since
    we can't tell when this may potentially happen, we assume the
    worst by forcing re-compensation for it at every point the VCPU
    task is descheduled.

    Signed-off-by: Zachary Amsden <zamsden@redhat.com>
    ---
    arch/x86/kvm/x86.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index 7fc4a55..52b6c21 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -1866,7 +1866,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    }

    kvm_x86_ops->vcpu_load(vcpu, cpu);
    - if (unlikely(vcpu->cpu != cpu)) {
    + if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) {
    /* Make sure TSC doesn't go backwards */
    s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
    native_read_tsc() - vcpu->arch.last_host_tsc;
    --
    1.7.1


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