From a16414dc8771bee6a2b99e0abaf52e414450ba3b Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <sebastien.boeuf@intel.com>
Date: Mon, 22 Jun 2020 15:13:45 +0200
Subject: [PATCH] vmm: Restore vCPUs in "paused" state

To follow a symmetrical model, and avoid potential race conditions, it's
important to restore a previously snapshot VM in a "paused" state.

The snapshot operation being valid only if the VM has been previously
paused.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
---
 vmm/src/cpu.rs | 47 +++++++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 22 deletions(-)

diff --git a/vmm/src/cpu.rs b/vmm/src/cpu.rs
index 136b3f6f4..3b8e9f48a 100644
--- a/vmm/src/cpu.rs
+++ b/vmm/src/cpu.rs
@@ -790,28 +790,6 @@ impl CpuManager {
                     vcpu_thread_barrier.wait();
 
                     loop {
-                        // vcpu.run() returns false on a KVM_EXIT_SHUTDOWN (triple-fault) so trigger a reset
-                        match vcpu.lock().unwrap().run() {
-                            Err(e) => {
-                                error!("VCPU generated error: {:?}", e);
-                                break;
-                            }
-                            Ok(true) => {}
-                            Ok(false) => {
-                                vcpu_run_interrupted.store(true, Ordering::SeqCst);
-                                reset_evt.write(1).unwrap();
-                                break;
-                            }
-                        }
-
-                        // We've been told to terminate
-                        if vcpu_kill_signalled.load(Ordering::SeqCst)
-                            || vcpu_kill.load(Ordering::SeqCst)
-                        {
-                            vcpu_run_interrupted.store(true, Ordering::SeqCst);
-                            break;
-                        }
-
                         // If we are being told to pause, we park the thread
                         // until the pause boolean is toggled.
                         // The resume operation is responsible for toggling
@@ -834,6 +812,28 @@ impl CpuManager {
                             vcpu_run_interrupted.store(true, Ordering::SeqCst);
                             break;
                         }
+
+                        // vcpu.run() returns false on a KVM_EXIT_SHUTDOWN (triple-fault) so trigger a reset
+                        match vcpu.lock().unwrap().run() {
+                            Err(e) => {
+                                error!("VCPU generated error: {:?}", e);
+                                break;
+                            }
+                            Ok(true) => {}
+                            Ok(false) => {
+                                vcpu_run_interrupted.store(true, Ordering::SeqCst);
+                                reset_evt.write(1).unwrap();
+                                break;
+                            }
+                        }
+
+                        // We've been told to terminate
+                        if vcpu_kill_signalled.load(Ordering::SeqCst)
+                            || vcpu_kill.load(Ordering::SeqCst)
+                        {
+                            vcpu_run_interrupted.store(true, Ordering::SeqCst);
+                            break;
+                        }
                     }
                 })
                 .map_err(Error::VcpuSpawn)?,
@@ -1332,6 +1332,9 @@ impl Snapshottable for CpuManager {
     fn restore(&mut self, snapshot: Snapshot) -> std::result::Result<(), MigratableError> {
         let vcpu_thread_barrier = Arc::new(Barrier::new((snapshot.snapshots.len() + 1) as usize));
 
+        // Restore the vCPUs in "paused" state.
+        self.vcpus_pause_signalled.store(true, Ordering::SeqCst);
+
         for (cpu_id, snapshot) in snapshot.snapshots.iter() {
             debug!("Restoring VCPU {}", cpu_id);
             let vcpu = self