vmm: memory_manager: Rely on physical bits for address space size

If the user provided a maximum physical bits value for the vCPUs, the
memory manager will adapt the guest physical address space accordingly
so that devices are not placed further than the specified value.

It's important to note that if the number exceed what is available on
the host, the smaller number will be picked.

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

vmm/src/vm.rs

@@ -38,6 +38,7 @@ use crate::{
     PciDeviceInfo, CPU_MANAGER_SNAPSHOT_ID, DEVICE_MANAGER_SNAPSHOT_ID, MEMORY_MANAGER_SNAPSHOT_ID,
 };
 use anyhow::anyhow;
+use arch::get_host_cpu_phys_bits;
 #[cfg(target_arch = "x86_64")]
 use arch::BootProtocol;
 use arch::EntryPoint;
@@ -51,6 +52,7 @@ use linux_loader::loader::elf::PvhBootCapability::PvhEntryPresent;
 use linux_loader::loader::KernelLoader;
 use seccomp::{SeccompAction, SeccompFilter};
 use signal_hook::{iterator::Signals, SIGINT, SIGTERM, SIGWINCH};
+use std::cmp;
 use std::collections::{BTreeMap, HashMap};
 use std::convert::TryInto;
 use std::ffi::CString;
@@ -431,6 +433,11 @@ impl VmmOps for VmOps {
     }
 }
 
+fn physical_bits(max_phys_bits: Option<u8>) -> u8 {
+    let host_phys_bits = get_host_cpu_phys_bits();
+    cmp::min(host_phys_bits, max_phys_bits.unwrap_or(host_phys_bits))
+}
+
 pub struct Vm {
     kernel: File,
     initramfs: Option<File>,
@@ -629,11 +636,13 @@ impl Vm {
         let vm = hypervisor.create_vm().unwrap();
         #[cfg(target_arch = "x86_64")]
         vm.enable_split_irq().unwrap();
+        let phys_bits = physical_bits(config.lock().unwrap().cpus.max_phys_bits);
         let memory_manager = MemoryManager::new(
             vm.clone(),
             &config.lock().unwrap().memory.clone(),
             None,
             false,
+            phys_bits,
         )
         .map_err(Error::MemoryManager)?;
 
@@ -697,12 +706,14 @@ impl Vm {
         let memory_manager = if let Some(memory_manager_snapshot) =
             snapshot.snapshots.get(MEMORY_MANAGER_SNAPSHOT_ID)
         {
+            let phys_bits = physical_bits(config.lock().unwrap().cpus.max_phys_bits);
             MemoryManager::new_from_snapshot(
                 memory_manager_snapshot,
                 vm.clone(),
                 &config.lock().unwrap().memory.clone(),
                 source_url,
                 prefault,
+                phys_bits,
             )
             .map_err(Error::MemoryManager)?
         } else {