Patch "KVM: x86: move steal time initialization to vcpu entry time" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: move steal time initialization to vcpu entry time

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-move-steal-time-initialization-to-vcpu-entry-time.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marcelo Tosatti <[email protected]>
Date: Wed, 14 Oct 2015 19:33:09 -0300
Subject: KVM: x86: move steal time initialization to vcpu entry time

From: Marcelo Tosatti <[email protected]>

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.

---
 arch/x86/kvm/x86.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

@@ -1941,6 +1941,8 @@ static void accumulate_steal_time(struct
 
 static void record_steal_time(struct kvm_vcpu *vcpu)
 {
+	accumulate_steal_time(vcpu);
+
 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
 		return;
 

@@ -2074,12 +2076,6 @@ int kvm_set_msr_common(struct kvm_vcpu *
 		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;

@@ -2758,7 +2754,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu
 		vcpu->cpu = cpu;
 	}
 
-	accumulate_steal_time(vcpu);
 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/kvm-x86-move-steal-time-initialization-to-vcpu-entry-time.patch