virtio-devices, vmm: vdpa: Implement live migration support

Vdpa now implements the Migratable trait, which allows the device to be
added to the DeviceTree and therefore allows live migrating any vDPA
device that supports being suspended.

Given a vDPA device can't be resumed from a suspended state without
having to reset everything, we don't support pause/resume for a vDPA
device, as well as snapshot/restore (which requires resume to be
supported).

In order for the migration to work locally, reusing the same device on
the same host machine, the vhost-vdpa handler is dropped after the
snapshot has been performed, which allows the destination VM to open the
device without any conflict about the device being busy.

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

virtio-devices/src/vdpa.rs

@@ -8,21 +8,27 @@ use crate::{
     VirtioInterruptType, DEVICE_ACKNOWLEDGE, DEVICE_DRIVER, DEVICE_DRIVER_OK, DEVICE_FEATURES_OK,
     VIRTIO_F_IOMMU_PLATFORM,
 };
+use anyhow::anyhow;
 use std::{
     collections::BTreeMap,
     io, result,
     sync::{atomic::Ordering, Arc, Mutex},
 };
 use thiserror::Error;
+use versionize::{VersionMap, Versionize, VersionizeResult};
+use versionize_derive::Versionize;
 use vhost::{
     vdpa::{VhostVdpa, VhostVdpaIovaRange},
-    vhost_kern::vdpa::VhostKernVdpa,
     vhost_kern::VhostKernFeatures,
+    vhost_kern::{vdpa::VhostKernVdpa, vhost_binding::VHOST_BACKEND_F_SUSPEND},
     VhostBackend, VringConfigData,
 };
 use virtio_queue::{Descriptor, Queue, QueueT};
 use vm_device::dma_mapping::ExternalDmaMapping;
 use vm_memory::{GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic};
+use vm_migration::{
+    Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable, VersionMapped,
+};
 use vm_virtio::{AccessPlatform, Translatable};
 use vmm_sys_util::eventfd::EventFd;
 
@@ -38,6 +44,8 @@ pub enum Error {
     GetAddressRange,
     #[error("Failed to get the available index from the virtio queue: {0}")]
     GetAvailableIndex(virtio_queue::Error),
+    #[error("Get virtio configuration size: {0}")]
+    GetConfigSize(vhost::Error),
     #[error("Get virtio device identifier: {0}")]
     GetDeviceId(vhost::Error),
     #[error("Failed to get backend specific features: {0}")]
@@ -82,13 +90,31 @@ pub enum Error {
 
 pub type Result<T> = std::result::Result<T, Error>;
 
+#[derive(Versionize)]
+pub struct VdpaState {
+    pub avail_features: u64,
+    pub acked_features: u64,
+    pub device_type: u32,
+    pub iova_range_first: u64,
+    pub iova_range_last: u64,
+    pub config: Vec<u8>,
+    pub queue_sizes: Vec<u16>,
+    pub backend_features: u64,
+}
+
+impl VersionMapped for VdpaState {}
+
 pub struct Vdpa {
     common: VirtioCommon,
     id: String,
+    mem: GuestMemoryAtomic<GuestMemoryMmap>,
+    device_path: String,
     vhost: Option<VhostKernVdpa<GuestMemoryAtomic<GuestMemoryMmap>>>,
     iova_range: VhostVdpaIovaRange,
     enabled_queues: BTreeMap<usize, bool>,
     backend_features: u64,
+    migrating: bool,
+    buffered_maps: Vec<(u64, u64, u64, bool)>,
 }
 
 impl Vdpa {
@@ -97,8 +123,29 @@ impl Vdpa {
         device_path: &str,
         mem: GuestMemoryAtomic<GuestMemoryMmap>,
         num_queues: u16,
+        restoring: bool,
     ) -> Result<Self> {
-        let mut vhost = VhostKernVdpa::new(device_path, mem).map_err(Error::CreateVhostVdpa)?;
+        if restoring {
+            return Ok(Vdpa {
+                common: VirtioCommon {
+                    queue_sizes: vec![1024; num_queues as usize],
+                    min_queues: num_queues,
+                    ..Default::default()
+                },
+                id,
+                mem,
+                device_path: device_path.to_string(),
+                vhost: None,
+                iova_range: VhostVdpaIovaRange { first: 0, last: 0 },
+                enabled_queues: BTreeMap::new(),
+                backend_features: 0,
+                migrating: false,
+                buffered_maps: Vec::new(),
+            });
+        }
+
+        let mut vhost =
+            VhostKernVdpa::new(device_path, mem.clone()).map_err(Error::CreateVhostVdpa)?;
         vhost.set_owner().map_err(Error::SetOwner)?;
         let device_type = vhost.get_device_id().map_err(Error::GetDeviceId)?;
         let queue_size = vhost.get_vring_num().map_err(Error::GetVringNum)?;
@@ -123,10 +170,14 @@ impl Vdpa {
                 ..Default::default()
             },
             id,
+            mem,
+            device_path: device_path.to_string(),
             vhost: Some(vhost),
             iova_range,
             enabled_queues: BTreeMap::new(),
             backend_features,
+            migrating: false,
+            buffered_maps: Vec::new(),
         })
     }
 
@@ -153,6 +204,7 @@ impl Vdpa {
         virtio_interrupt: &Arc<dyn VirtioInterrupt>,
         queues: Vec<(usize, Queue, EventFd)>,
     ) -> Result<()> {
+        assert!(self.vhost.is_some());
         self.vhost
             .as_ref()
             .unwrap()
@@ -224,6 +276,8 @@ impl Vdpa {
                 .unwrap()
                 .set_vring_kick(*queue_index, queue_evt)
                 .map_err(Error::SetVringKick)?;
+
+            self.enabled_queues.insert(*queue_index, false);
         }
 
         // Setup the config eventfd if there is one
@@ -249,6 +303,7 @@ impl Vdpa {
     fn reset_vdpa(&mut self) -> Result<()> {
         self.enable_vrings(false)?;
 
+        assert!(self.vhost.is_some());
         self.vhost
             .as_ref()
             .unwrap()
@@ -256,7 +311,19 @@ impl Vdpa {
             .map_err(Error::SetStatus)
     }
 
-    fn dma_map(&self, iova: u64, size: u64, host_vaddr: *const u8, readonly: bool) -> Result<()> {
+    fn dma_map(
+        &mut self,
+        iova: u64,
+        size: u64,
+        host_vaddr: *const u8,
+        readonly: bool,
+    ) -> Result<()> {
+        if self.vhost.is_none() {
+            self.buffered_maps
+                .push((iova, size, host_vaddr as u64, readonly));
+            return Ok(());
+        }
+
         let iova_last = iova + size - 1;
         if iova < self.iova_range.first || iova_last > self.iova_range.last {
             return Err(Error::InvalidIovaRange(iova, iova_last));
@@ -283,6 +350,56 @@ impl Vdpa {
             .dma_unmap(iova, size)
             .map_err(Error::DmaUnmap)
     }
+
+    fn state(&self) -> Result<VdpaState> {
+        assert!(self.vhost.is_some());
+        let config_size = self
+            .vhost
+            .as_ref()
+            .unwrap()
+            .get_config_size()
+            .map_err(Error::GetConfigSize)?;
+        let mut config = vec![0; config_size as usize];
+        self.read_config(0, config.as_mut_slice());
+
+        Ok(VdpaState {
+            avail_features: self.common.avail_features,
+            acked_features: self.common.acked_features,
+            device_type: self.common.device_type,
+            queue_sizes: self.common.queue_sizes.clone(),
+            iova_range_first: self.iova_range.first,
+            iova_range_last: self.iova_range.last,
+            config,
+            backend_features: self.backend_features,
+        })
+    }
+
+    fn set_state(&mut self, state: &VdpaState) -> Result<()> {
+        self.common.avail_features = state.avail_features;
+        self.common.acked_features = state.acked_features;
+        self.common.device_type = state.device_type;
+        self.common.queue_sizes = state.queue_sizes.clone();
+        self.iova_range = VhostVdpaIovaRange {
+            first: state.iova_range_first,
+            last: state.iova_range_last,
+        };
+        self.backend_features = state.backend_features;
+
+        let mut vhost = VhostKernVdpa::new(self.device_path.as_str(), self.mem.clone())
+            .map_err(Error::CreateVhostVdpa)?;
+        vhost.set_owner().map_err(Error::SetOwner)?;
+        vhost.set_backend_features_acked(self.backend_features);
+        self.vhost = Some(vhost);
+
+        self.write_config(0, state.config.as_slice());
+
+        let maps: Vec<(u64, u64, u64, bool)> = self.buffered_maps.drain(..).collect();
+        for (iova, size, host_vaddr, readonly) in maps {
+            self.dma_map(iova, size, host_vaddr as *const u8, readonly)?;
+        }
+
+        Ok(())
+    }
 }
 
 impl VirtioDevice for Vdpa {
@@ -349,6 +466,89 @@ impl VirtioDevice for Vdpa {
     }
 }
 
+impl Pausable for Vdpa {
+    fn pause(&mut self) -> std::result::Result<(), MigratableError> {
+        if !self.migrating {
+            Err(MigratableError::Pause(anyhow!(
+                "Can't pause a vDPA device outside live migration"
+            )))
+        } else {
+            Ok(())
+        }
+    }
+
+    fn resume(&mut self) -> std::result::Result<(), MigratableError> {
+        if !self.migrating {
+            Err(MigratableError::Resume(anyhow!(
+                "Can't resume a vDPA device outside live migration"
+            )))
+        } else {
+            Ok(())
+        }
+    }
+}
+
+impl Snapshottable for Vdpa {
+    fn id(&self) -> String {
+        self.id.clone()
+    }
+
+    fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
+        if !self.migrating {
+            return Err(MigratableError::Snapshot(anyhow!(
+                "Can't snapshot a vDPA device outside live migration"
+            )));
+        }
+
+        let snapshot = Snapshot::new_from_versioned_state(
+            &self.id(),
+            &self.state().map_err(|e| {
+                MigratableError::Snapshot(anyhow!("Error snapshotting vDPA device: {:?}", e))
+            })?,
+        )?;
+
+        // Force the vhost handler to be dropped in order to close the vDPA
+        // file. This will ensure the device can be accessed if the VM is
+        // migrated on the same host machine.
+        self.vhost.take();
+
+        Ok(snapshot)
+    }
+
+    fn restore(&mut self, snapshot: Snapshot) -> std::result::Result<(), MigratableError> {
+        self.set_state(&snapshot.to_versioned_state(&self.id)?)
+            .map_err(|e| {
+                MigratableError::Restore(anyhow!("Error restoring vDPA device: {:?}", e))
+            })?;
+        Ok(())
+    }
+}
+
+impl Transportable for Vdpa {}
+
+impl Migratable for Vdpa {
+    fn start_migration(&mut self) -> std::result::Result<(), MigratableError> {
+        self.migrating = true;
+        // Given there's no way to track dirty pages, we must suspend the
+        // device as soon as the migration process starts.
+        if self.backend_features & (1 << VHOST_BACKEND_F_SUSPEND) != 0 {
+            assert!(self.vhost.is_some());
+            self.vhost.as_ref().unwrap().suspend().map_err(|e| {
+                MigratableError::StartMigration(anyhow!("Error suspending vDPA device: {:?}", e))
+            })
+        } else {
+            Err(MigratableError::StartMigration(anyhow!(
+                "vDPA device can't be suspended"
+            )))
+        }
+    }
+
+    fn complete_migration(&mut self) -> std::result::Result<(), MigratableError> {
+        self.migrating = false;
+        Ok(())
+    }
+}
+
 pub struct VdpaDmaMapping<M: GuestAddressSpace> {
     device: Arc<Mutex<Vdpa>>,
     memory: Arc<M>,

vmm/src/device_manager.rs

@@ -2852,6 +2852,7 @@ impl DeviceManager {
                 device_path,
                 self.memory_manager.lock().unwrap().guest_memory(),
                 vdpa_cfg.num_queues as u16,
+                self.restoring,
             )
             .map_err(DeviceManagerError::CreateVdpa)?,
         ));
@@ -2865,7 +2866,7 @@ impl DeviceManager {
         self.device_tree
             .lock()
             .unwrap()
-            .insert(id.clone(), device_node!(id));
+            .insert(id.clone(), device_node!(id, vdpa_device));
 
         Ok(MetaVirtioDevice {
             virtio_device: vdpa_device as Arc<Mutex<dyn virtio_devices::VirtioDevice>>,