Commit e5aa9bc4 authored Mar 11, 2016 by Marcelo Tosatti Committed by Sasha Levin Mar 13, 2016

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

[ Upstream commit 7cae2bedcbd4680b155999655e49c27b9cf020fa ]

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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent b769d469

arch/x86/kvm/x86.c

+2 −7

Original line number	Diff line number	Diff line
		@@ -2065,6 +2065,8 @@ 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;

		@@ -2198,12 +2200,6 @@ 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;
		@@ -2903,7 +2899,6 @@ 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);
		}