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    Subject[PATCH 3.4 107/107] KVM: x86: move steal time initialization to vcpu entry time
    Date
    From: Marcelo Tosatti <mtosatti@redhat.com>

    3.4.111-rc1 review patch. If anyone has any objections, please let me know.

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


    commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream.

    As reported at https://bugs.launchpad.net/qemu/+bug/1494350,
    it is possible to have vcpu->arch.st.last_steal initialized
    from a thread other than vcpu thread, say the iothread, via
    KVM_SET_MSRS.

    Which can cause an overflow later (when subtracting from vcpu threads
    sched_info.run_delay).

    To avoid that, move steal time accumulation to vcpu entry time,
    before copying steal time data to guest.

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
    Reviewed-by: David Matlack <dmatlack@google.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Zefan Li <lizefan@huawei.com>
    ---
    arch/x86/kvm/x86.c | 9 ++-------
    1 file changed, 2 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index 4ad2b7b..9cc83e2 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -1545,6 +1545,8 @@ static void accumulate_steal_time(struct kvm_vcpu *vcpu)

    static void record_steal_time(struct kvm_vcpu *vcpu)
    {
    + accumulate_steal_time(vcpu);
    +
    if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
    return;

    @@ -1665,12 +1667,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
    if (!(data & KVM_MSR_ENABLED))
    break;

    - vcpu->arch.st.last_steal = current->sched_info.run_delay;
    -
    - preempt_disable();
    - accumulate_steal_time(vcpu);
    - preempt_enable();
    -
    kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);

    break;
    @@ -2327,7 +2323,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    vcpu->cpu = cpu;
    }

    - accumulate_steal_time(vcpu);
    kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
    }

    --
    1.9.1
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