nested migration

how do we treat nested data on migration:

Situations:

A. Sync of v cpu nested data, do it on QEMU migration only

			QEMU	KVM
vcpu->nested.vmxon	true	true  : someone already turned on nested vmx, do not allow do anything, return error
			true	false : proper state, it's actually migration with nested vm -> load vcpu nested data from QEMU to kvm
			false   true  : on vcpu nested vmx is turned on but this is unexpected for qemu, since on migration it expects a just-initialized vcpu
			false	false :	don't need to do anything about nested cpu

From KVM perspective it's reasonable to allow to turn on nested VMX only when the nested is currently off

KVM:
to enable nested vmx on vcpu it's needed:

Preconditions:
1. vcpu has been created already with vmx_create_vcpu
2. the guest memory has been fully restored

1. enter_vmx_operation(vcpu)
2. if (enable_shadow_vmcs) set vcpu->nested.sync_shadow_vmcs = true;
3. set MSRS:
	MSR_IA32_VMX_BASIC
	MSR_IA32_VMX_MISC
	MSR_IA32_VMX_CR0_FIXED0
	MSR_IA32_VMX_CR0_FIXED1
	MSR_IA32_VMX_CR4_FIXED0
	MSR_IA32_VMX_CR4_FIXED1
	MSR_IA32_VMX_VMCS_ENUM
	MSR_IA32_VMX_PROCBASED_CTLS2
	MSR_IA32_VMX_EPT_VPID_CAP
	MSR_IA32_VMX_TRUE_PINBASED_CTLS
	MSR_IA32_VMX_TRUE_PROCBASED_CTLS
	MSR_IA32_VMX_TRUE_EXIT_CTLS
	MSR_IA32_VMX_TRUE_ENTRY_CTLS
4. vmx_set_msr_bitmap(vcpu)
5. load a saved nested state



(handle_vmlaunch; handle_vmresume) -> nested_vmx_run -> enter_vmx_non_root_mode -> nested_get_vmcs12_pages