[Devel] [PATCH RHEL7 COMMIT] ms/KVM: x86: move steal time initialization to vcpu entry time

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.18.2.vz7.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.18.2.vz7.14.5
------>
commit 4a055bb845eda81847c8e2b2233ba8ac3a889ab6
Author: Marcelo Tosatti <mtosatti at redhat.com>
Date:   Fri May 20 16:38:02 2016 +0400

    ms/KVM: x86: move steal time initialization to vcpu entry time
    
    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 at redhat.com>
    Reviewed-by: David Matlack <dmatlack at google.com>
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    (cherry picked from commit 7cae2bedcbd4680b155999655e49c27b9cf020fa)
    
    https://jira.sw.ru/browse/PSBM-46737
    
    Signed-off-by: Roman Kagan <rkagan at virtuozzo.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 ca78e5e..146c34a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2057,6 +2057,8 @@ 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;
 
@@ -2207,12 +2209,6 @@ 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;
@@ -2826,7 +2822,6 @@ 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);
 }