vmm: device_manager: Tie PCI bus to NUMA node 0

Make sure the unique PCI bus is tied to the default NUMA node 0, and
update the documentation to let the users know about this special case.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/device_manager.rs

@@ -3744,6 +3744,14 @@ impl Aml for DeviceManager {
         let supp = aml::Name::new("SUPP".into(), &aml::ZERO);
         pci_dsdt_inner_data.push(&supp);
 
+        // Since Cloud Hypervisor supports only one PCI bus, it can be tied
+        // to the NUMA node 0. It's up to the user to organize the NUMA nodes
+        // so that the PCI bus relates to the expected vCPUs and guest RAM.
+        let proximity_domain = 0u32;
+        let pxm_return = aml::Return::new(&proximity_domain);
+        let pxm = aml::Method::new("_PXM".into(), 0, false, vec![&pxm_return]);
+        pci_dsdt_inner_data.push(&pxm);
+
         let pci_dsm = PciDsmMethod {};
         pci_dsdt_inner_data.push(&pci_dsm);