xl dmesg | grep -i hvm

(XEN) HVM: ASIDs enabled.
(XEN) HVM: VMX enabled
(XEN) HVM: Hardware Assisted Paging (HAP) detected
(XEN) HVM: HAP page sizes: 4kB, 2MB

(XEN) Enabling APIC mode:  Flat.  Using 1 I/O APICs
(XEN) I/O virtualisation enabled

# modprobe xen-pciback
# xl pci-assignable-add xx:yy.z

sudo xl pci-assignable-list

sudo nano /etc/xen/ubuntu.hvm

pci = ['0000:xx:yy.z']

sudo xl create /etc/xen/ubuntu.hvm

Parsing config from /etc/xen/ubuntu.hvm
libxl: error: libxl_pci.c:1111:do_pci_add: Domain 2:xc_assign_device failed: Cannot allocate memory
libxl: error: libxl_pci.c:1306:libxl__add_pcidevs: Domain 2:libxl_device_pci_add failed: -3
libxl: error: libxl_create.c:1458:domcreate_attach_devices: Domain 2:unable to add pci devices
libxl: error: libxl_domain.c:1003:libxl__destroy_domid: Domain 2:Non-existant domain
libxl: error: libxl_domain.c:962:domain_destroy_callback: Domain 2:Unable to destroy guest
libxl: error: libxl_domain.c:889:domain_destroy_cb: Domain 2:Destruction of domain failed