Re: [PATCH] KVM: x86: move steal time initialization to vcpu entry time

[Paolo Bonzini]

On 15/10/2015 19:10, David Matlack 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 
> 
> Reviewed-by: David Matlack 

Applied to kvm/queue.  Thanks Marcelo, and thanks David for the review.

Paolo
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Re: [PATCH] KVM: x86: move steal time initialization to vcpu entry time

[David Matlack]

On Wed, Oct 14, 2015 at 3:33 PM, Marcelo Tosatti  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 

Reviewed-by: David Matlack 

>
> 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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[PATCH] KVM: x86: move steal time initialization to vcpu entry time

[Marcelo Tosatti]

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 

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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