Re: [PATCH v2 2/3] KVM: nVMX: add kvm_nested_vmlaunch_resume tracepoint

[Paolo Bonzini]

On 15/01/21 01:14, Sean Christopherson wrote:
> > +	trace_kvm_nested_vmlaunch_resume(kvm_rip_read(vcpu),
> Hmm, won't this RIP be wrong for the migration case?  I.e. it'll be L2, not L1
> as is the case for the "true" nested VM-Enter path.

It will be the previous RIP---might as well be 0xfffffff0 depending on 
what userspace does.  I don't think you can do much better than that, 
using vmcs12->host_rip would be confusing in the SMM case.

> > +					 vmx->nested.current_vmptr,
> > +					 vmcs12->guest_rip,
> > +					 vmcs12->vm_entry_intr_info_field);
> The placement is a bit funky.  I assume you put it here so that calls from
> vmx_set_nested_state() also get traced.  But, that also means
> vmx_pre_leave_smm() will get traced, and it also creates some weirdness where
> some nested VM-Enters that VM-Fail will get traced, but others will not.
>
> Tracing vmx_pre_leave_smm() isn't necessarily bad, but it could be confusing,
> especially if the debugger looks up the RIP and sees RSM.  Ditto for the
> migration case.

Actually tracing vmx_pre_leave_smm() is good, and pointing to RSM makes 
sense so I'm not worried about that.

Paolo