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

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

[Liang Chen]

From: Marcelo Tosatti <mtosatti@redhat.com>

commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream

This patch is needed on lts 3.4, 3.10, 3.12, 3.14, 3.18, and 4.1 for
the same issue. Can you please to pick it up?

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>
---
 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 d6e8bd0..7d4f352 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1987,6 +1987,8 @@ 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;
 
@@ -2120,12 +2122,6 @@ 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;
@@ -2808,7 +2804,6 @@ 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

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

[Greg KH]

On Fri, Mar 11, 2016 at 04:53:11PM +0800, Liang Chen wrote:
> From: Marcelo Tosatti <mtosatti@redhat.com>
> 
> commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream
> 
> This patch is needed on lts 3.4, 3.10, 3.12, 3.14, 3.18, and 4.1 for
> the same issue. Can you please to pick it up?

Applied to 3.10 and 3.14-stable trees now, thanks.

greg k-h

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

[Zefan Li]

On 2016/3/11 16:53, Liang Chen wrote:
> From: Marcelo Tosatti <mtosatti@redhat.com>
> 
> commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream
> 
> This patch is needed on lts 3.4, 3.10, 3.12, 3.14, 3.18, and 4.1 for
> the same issue. Can you please to pick it up?
> 

Sure. I'll queue it up for 3.4.y. Thanks!

> 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>

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

[Luis Henriques]

On Fri, Mar 11, 2016 at 04:53:11PM +0800, Liang Chen wrote:
> From: Marcelo Tosatti <mtosatti@redhat.com>
> 
> commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream
> 
> This patch is needed on lts 3.4, 3.10, 3.12, 3.14, 3.18, and 4.1 for
> the same issue. Can you please to pick it up?

Thanks, I'm also including this in the 3.16 kernel.

Cheers,
--
Lu�s

> 
> 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>
> ---
>  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 d6e8bd0..7d4f352 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1987,6 +1987,8 @@ 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;
>  
> @@ -2120,12 +2122,6 @@ 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;
> @@ -2808,7 +2804,6 @@ 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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