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    Subject[PATCH 10/11] KVM: Fix local apic timer divide by zero
    Date
    From: Kevin Pedretti <kevin.pedretti@gmail.com>

    kvm_lapic_reset() was initializing apic->timer.divide_count to 0,
    which could potentially lead to a divide by zero error in
    apic_get_tmcct(). Any guest that reads the APIC's CCR (current count)
    register before setting DCR (divide configuration) would trigger a divide
    by zero exception in the host kernel, leading to a host-OS crash.

    This patch results in apic->timer.divide_count being initialized to
    2 at reset, eliminating the bug (DCR=0 at reset, meaning divide by 2).

    Signed-off-by: Kevin Pedretti <kevin.pedretti@gmail.com>
    Signed-off-by: Avi Kivity <avi@qumranet.com>
    ---
    drivers/kvm/lapic.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/drivers/kvm/lapic.c b/drivers/kvm/lapic.c
    index a190587..443730e 100644
    --- a/drivers/kvm/lapic.c
    +++ b/drivers/kvm/lapic.c
    @@ -853,7 +853,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
    apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);
    apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);
    }
    - apic->timer.divide_count = 0;
    + update_divide_count(apic);
    atomic_set(&apic->timer.pending, 0);
    if (vcpu->vcpu_id == 0)
    vcpu->apic_base |= MSR_IA32_APICBASE_BSP;
    --
    1.5.3
    -
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