vm-virtio, vmm, vfio: Store GuestMemoryMmap in an Arc<ArcSwap<T>>

This allows us to change the memory map that is being used by the
devices via an atomic swap (by replacing the map with another one). The
ArcSwap provides the mechanism for atomically swapping from to another
whilst still giving good read performace. It is inside an Arc so that we
can use a single ArcSwap for all users.

Not covered by this change is replacing the GuestMemoryMmap itself.

This change also removes some vertical whitespace from use blocks in the
files that this commit also changed. Vertical whitespace was being used
inconsistently and broke rustfmt's behaviour of ordering the imports as
it would only do it within the block.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/vm.rs

@@ -29,19 +29,17 @@ use crate::cpu;
 use crate::device_manager::{get_win_size, Console, DeviceManager, DeviceManagerError};
 use crate::memory_manager::{get_host_cpu_phys_bits, Error as MemoryManagerError, MemoryManager};
 use anyhow::anyhow;
+use arc_swap::ArcSwap;
 use arch::layout;
 use devices::{ioapic, HotPlugNotificationType};
 use kvm_bindings::{kvm_enable_cap, kvm_userspace_memory_region, KVM_CAP_SPLIT_IRQCHIP};
 use kvm_ioctls::*;
-
 use linux_loader::cmdline::Cmdline;
 use linux_loader::loader::KernelLoader;
 use signal_hook::{iterator::Signals, SIGINT, SIGTERM, SIGWINCH};
 use std::ffi::CString;
 use std::fs::File;
 use std::io;
-use std::ops::Deref;
-
 use std::sync::{Arc, Mutex, RwLock};
 use std::{result, str, thread};
 use vm_allocator::{GsiApic, SystemAllocator};
@@ -159,7 +157,7 @@ pub enum Error {
 pub type Result<T> = result::Result<T, Error>;
 
 pub struct VmInfo<'a> {
-    pub memory: &'a Arc<RwLock<GuestMemoryMmap>>,
+    pub memory: &'a Arc<ArcSwap<GuestMemoryMmap>>,
     pub vm_fd: &'a Arc<VmFd>,
     pub vm_cfg: Arc<Mutex<VmConfig>>,
 }
@@ -371,9 +369,9 @@ impl Vm {
 
         let cmdline_cstring = CString::new(cmdline).map_err(|_| Error::CmdLine)?;
         let guest_memory = self.memory_manager.lock().as_ref().unwrap().guest_memory();
-        let mem = guest_memory.read().unwrap();
+        let mem = guest_memory.load_full();
         let entry_addr = match linux_loader::loader::Elf::load(
-            mem.deref(),
+            mem.as_ref(),
             None,
             &mut self.kernel,
             Some(arch::layout::HIGH_RAM_START),
@@ -381,7 +379,7 @@ impl Vm {
             Ok(entry_addr) => entry_addr,
             Err(linux_loader::loader::Error::InvalidElfMagicNumber) => {
                 linux_loader::loader::BzImage::load(
-                    mem.deref(),
+                    mem.as_ref(),
                     None,
                     &mut self.kernel,
                     Some(arch::layout::HIGH_RAM_START),
@@ -392,7 +390,7 @@ impl Vm {
         };
 
         linux_loader::loader::load_cmdline(
-            mem.deref(),
+            mem.as_ref(),
             arch::layout::CMDLINE_START,
             &cmdline_cstring,
         )