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/memory_manager.rs

@@ -12,7 +12,7 @@ use acpi_tables::{aml, aml::Aml};
 use anyhow::anyhow;
 #[cfg(target_arch = "x86_64")]
 use arch::x86_64::{SgxEpcRegion, SgxEpcSection};
-use arch::{get_host_cpu_phys_bits, layout, RegionType};
+use arch::{layout, RegionType};
 #[cfg(target_arch = "x86_64")]
 use devices::ioapic;
 #[cfg(target_arch = "x86_64")]
@@ -256,8 +256,8 @@ const SELECTION_OFFSET: u64 = 0;
 // The MMIO address space size is subtracted with the size of a 4k page. This
 // is done on purpose to workaround a Linux bug when the VMM allocates devices
 // at the end of the addressable space.
-fn mmio_address_space_size() -> u64 {
-    (1 << get_host_cpu_phys_bits()) - 0x1000
+fn mmio_address_space_size(phys_bits: u8) -> u64 {
+    (1 << phys_bits) - 0x1000
 }
 
 impl BusDevice for MemoryManager {
@@ -448,6 +448,7 @@ impl MemoryManager {
         config: &MemoryConfig,
         ext_regions: Option<Vec<MemoryRegion>>,
         prefault: bool,
+        phys_bits: u8,
     ) -> Result<Arc<Mutex<MemoryManager>>, Error> {
         let user_provided_zones = config.size == 0;
         let mut allow_mem_hotplug: bool = false;
@@ -585,7 +586,8 @@ impl MemoryManager {
 
         let boot_guest_memory = guest_memory.clone();
 
-        let end_of_device_area = GuestAddress(mmio_address_space_size() - 1);
+        let mmio_address_space_size = mmio_address_space_size(phys_bits);
+        let end_of_device_area = GuestAddress(mmio_address_space_size - 1);
 
         let mut start_of_device_area =
             MemoryManager::start_addr(guest_memory.last_addr(), allow_mem_hotplug)?;
@@ -656,7 +658,7 @@ impl MemoryManager {
                 #[cfg(target_arch = "x86_64")]
                 (1 << 16 as GuestUsize),
                 GuestAddress(0),
-                mmio_address_space_size(),
+                mmio_address_space_size,
                 layout::MEM_32BIT_DEVICES_START,
                 layout::MEM_32BIT_DEVICES_SIZE,
                 #[cfg(target_arch = "x86_64")]
@@ -740,6 +742,7 @@ impl MemoryManager {
         config: &MemoryConfig,
         source_url: &str,
         prefault: bool,
+        phys_bits: u8,
     ) -> Result<Arc<Mutex<MemoryManager>>, Error> {
         let url = Url::parse(source_url).unwrap();
         /* url must be valid dir which is verified in recv_vm_snapshot() */
@@ -777,7 +780,7 @@ impl MemoryManager {
                 }
             }
 
-            MemoryManager::new(vm, config, Some(ext_regions), prefault)
+            MemoryManager::new(vm, config, Some(ext_regions), prefault, phys_bits)
         } else {
             Err(Error::Restore(MigratableError::Restore(anyhow!(
                 "Could not find {}-section from snapshot",

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 {