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
