Re: [PATCH v5] KVM: nVMX: Fully support of nested VMX preemption timer

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/09/2013 19:47, Paolo Bonzini ha scritto:
> 
> If I only apply this hunk, which disables the preemption timer while
> in L1:
> 
> @@ -8396,6 +8375,8 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu)
> 
>         load_vmcs12_host_state(vcpu, vmcs12);
> 
> +       vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, vmx_pin_based_exec_ctrl(vmx));
> +
>         /* Update TSC_OFFSET if TSC was changed while L2 ran */
>         vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
> 
> then the testcase works for somewhat larger values of the preemption timer
> (up to ~1500000 TSC cycles), but then fails.

I mean if I apply it on top of current kvm/next, without Arthur's patch.

If I apply the hunk on top of Arthur's patch nothing changes and the
timer testcase starts breaking around ~65000 TSC cycles.

It is a bit problematic that adding printks changes something, so that
the test starts passing.  I haven't tried tracepoints yet.

Jan, which L1 is using the preemption timer?  Any reason why you added
it?  I wonder if it isn't better to revert it, since it is quite broken.

Paolo