On Wed, Oct 14, 2015 at 3:33 PM, Marcelo Tosatti <mtosa...@redhat.com> wrote:
>
> 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 <mtosa...@redhat.com>
Reviewed-by: David Matlack <dmatl...@google.com>
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8f0f6ec..0e0332e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2030,6 +2030,8 @@ 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;
>
> @@ -2182,12 +2184,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct
> msr_data *msr_info)
> 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;
> @@ -2830,7 +2826,6 @@ 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);
> }
>
> --
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