On 11/01/2018 03:47, Tim Chen wrote: > 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. Of course. But these patches are just an initial version for a host that doesn't support IBRS. Paolo
