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@redhat.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 7 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e33aebbf189e..9e9c226cb79d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1903,6 +1903,8 @@ 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;
 
@@ -2053,12 +2055,6 @@ 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;
@@ -2634,7 +2630,6 @@ 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);
 }