vm-virtio: Implement userspace_mappings() for virtio-pmem

When hot-unplugging the virtio-pmem from the VM, we don't remove the
associated userspace mapping. This patch will let us fix this in a
following patch. For now, it simply adapts the code so that the Pmem
device knows about the mapping associated with it. By knowing about it,
it can expose it to the caller through the new userspace_mappings()
function.

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

vmm/src/device_manager.rs

@@ -1569,22 +1569,31 @@ impl DeviceManager {
                 },
         )
         .map_err(DeviceManagerError::NewMmapRegion)?;
-        let addr: u64 = mmap_region.as_ptr() as u64;
+        let host_addr: u64 = mmap_region.as_ptr() as u64;
 
-        self.memory_manager
+        let mem_slot = self
+            .memory_manager
             .lock()
             .unwrap()
             .create_userspace_mapping(
                 pmem_guest_addr.raw_value(),
                 size,
-                addr,
+                host_addr,
                 pmem_cfg.mergeable,
                 pmem_cfg.discard_writes,
             )
             .map_err(DeviceManagerError::MemoryManager)?;
 
+        let mapping = vm_virtio::UserspaceMapping {
+            host_addr,
+            mem_slot,
+            addr: pmem_guest_addr,
+            len: size,
+            mergeable: pmem_cfg.mergeable,
+        };
+
         let virtio_pmem_device = Arc::new(Mutex::new(
-            vm_virtio::Pmem::new(file, pmem_guest_addr, mmap_region, pmem_cfg.iommu)
+            vm_virtio::Pmem::new(file, pmem_guest_addr, mapping, mmap_region, pmem_cfg.iommu)
                 .map_err(DeviceManagerError::CreateVirtioPmem)?,
         ));