vmm: Add RwLock to the GuestMemoryMmap

Following the refactoring of the code allowing multiple threads to
access the same instance of the guest memory, this patch goes one step
further by adding RwLock to it. This anticipates the future need for
being able to modify the content of the guest memory at runtime.

The reasons for adding regions to an existing guest memory could be:
- Add virtio-pmem and virtio-fs regions after the guest memory was
  created.
- Support future hotplug of devices, memory, or anything that would
  require more memory at runtime.

Because most of the time, the lock will be taken as read only, using
RwLock instead of Mutex is the right approach.

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

vfio/src/vfio_device.rs

@@ -14,7 +14,7 @@ use std::mem;
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::os::unix::prelude::FileExt;
 use std::path::{Path, PathBuf};
-use std::sync::Arc;
+use std::sync::{Arc, RwLock};
 use std::u32;
 use vfio_bindings::bindings::vfio::*;
 use vfio_ioctls::*;
@@ -513,7 +513,7 @@ pub struct VfioDevice {
     group: VfioGroup,
     regions: Vec<VfioRegion>,
     irqs: HashMap<u32, VfioIrq>,
-    mem: Arc<GuestMemoryMmap>,
+    mem: Arc<RwLock<GuestMemoryMmap>>,
 }
 
 impl VfioDevice {
@@ -523,7 +523,7 @@ impl VfioDevice {
     pub fn new(
         sysfspath: &Path,
         device_fd: Arc<DeviceFd>,
-        mem: Arc<GuestMemoryMmap>,
+        mem: Arc<RwLock<GuestMemoryMmap>>,
     ) -> Result<Self> {
         let uuid_path: PathBuf = [sysfspath, Path::new("iommu_group")].iter().collect();
         let group_path = uuid_path.read_link().map_err(|_| VfioError::InvalidPath)?;
@@ -773,7 +773,7 @@ impl VfioDevice {
     /// Add all guest memory regions into vfio container's iommu table,
     /// then vfio kernel driver could access guest memory from gfn
     pub fn setup_dma_map(&self) -> Result<()> {
-        self.mem.with_regions(|_index, region| {
+        self.mem.read().unwrap().with_regions(|_index, region| {
             self.vfio_dma_map(
                 region.start_addr().raw_value(),
                 region.len() as u64,
@@ -786,7 +786,7 @@ impl VfioDevice {
     /// remove all guest memory regions from vfio containers iommu table
     /// then vfio kernel driver couldn't access this guest memory
     pub fn unset_dma_map(&self) -> Result<()> {
-        self.mem.with_regions(|_index, region| {
+        self.mem.read().unwrap().with_regions(|_index, region| {
             self.vfio_dma_unmap(region.start_addr().raw_value(), region.len() as u64)
         })?;
         Ok(())