Instead of using flip_arch_lbr_ctl, SMM should save the value of the MSR
in kvm_x86_ops->enter_smm, and restore it in kvm_x86_ops->leave_smm
(feel free to do it only if guest_cpuid_has(vcpu, X86_FEATURE_LM), i.e.
the 32-bit case can be ignored).
In the case of migration in SMM, I assume kvm_x86_ops->enter_smm() called in source side
and kvm_x86_ops->leave_smm() is called at destination, then should the saved LBREn be transferred
to destination too? The destination can rely on the bit to defer setting LBREn bit in
VMCS until kvm_x86_ops->leave_smm() is called. is it good? thanks!