Messages in this thread | | | Subject | Re: [PATCH 3/7] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD down to the guest | From | Tim Chen <> | Date | Wed, 10 Jan 2018 18:47:06 -0800 |
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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
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