KVM: x86: move steal time initialization to vcpu entry time
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Message ID 20151014223309.GA13900@amt.cnet
State New
Headers show

Commit Message

Marcelo Tosatti Oct. 14, 2015, 10:33 p.m. UTC
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>

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Comments

David Matlack Oct. 15, 2015, 5:10 p.m. UTC | #1
On Wed, Oct 14, 2015 at 3:33 PM, Marcelo Tosatti <mtosatti@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 <mtosatti@redhat.com>

Reviewed-by: David Matlack <dmatlack@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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Paolo Bonzini Oct. 16, 2015, 8:34 a.m. UTC | #2
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 <mtosatti@redhat.com>
> 
> Reviewed-by: David Matlack <dmatlack@google.com>

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

Paolo
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Patch
diff mbox

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);
 }