On 01/08/2018 10:08 AM, Paolo Bonzini wrote: > @@ -9597,6 +9620,9 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) > > pt_guest_enter(vmx); > > + if (have_spec_ctrl && vmx->spec_ctrl != 0) > + wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); > + Say host uses IBRS (have_spec_ctrl==1), and have IBRS set to 1. And say guest's vmx->spec_ctrl is 0 and not using IBRS. We will be leaving IBRS msr as 1 and won't be switching it to 0 before entering guest. Guest will be running with incorrect IBRS value. Seems like the correct logic is if (host_supports_ibrs) /* switch IBRS if host and guest ibrs differs */ if ((host_uses_ibrs && vmx->spec_ctrl == 0) || /* host IBRS 1, guest IBRS 0 */ (!host_uses_ibrs && vmx->spec_ctrl == 1)) /* host IBRS 0, guest IBRS 1 */ wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); } Your have_spec_ctrl logic specifies that IBRS is available. But that doesn't necessarily mean that we will use IBRS in host. Tim
