fix(test): dont drop guest memory before using it

Dropping a GuestMemoryMmap causes the memory to get unmapped, so if we
try to KVM_RUN after dropping it, we'll just get EFAULT.

Admittedly no idea how we didn't run into this issue before.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/vstate/vcpu/mod.rs

@@ -965,7 +965,7 @@ pub(crate) mod tests {
         entry_addr.unwrap().kernel_load
     }
 
-    fn vcpu_configured_for_boot() -> (VcpuHandle, vmm_sys_util::eventfd::EventFd) {
+    fn vcpu_configured_for_boot() -> (VcpuHandle, EventFd, GuestMemoryMmap) {
         Vcpu::register_kick_signal_handler();
         // Need enough mem to boot linux.
         let mem_size = 64 << 20;
@@ -1017,7 +1017,7 @@ pub(crate) mod tests {
         // Wait for vCPUs to initialize their TLS before moving forward.
         barrier.wait();
 
-        (vcpu_handle, vcpu_exit_evt)
+        (vcpu_handle, vcpu_exit_evt, vm_mem)
     }
 
     #[test]
@@ -1151,7 +1151,7 @@ pub(crate) mod tests {
 
     #[test]
     fn test_vcpu_pause_resume() {
-        let (vcpu_handle, vcpu_exit_evt) = vcpu_configured_for_boot();
+        let (vcpu_handle, vcpu_exit_evt, _mem) = vcpu_configured_for_boot();
 
         // Queue a Resume event, expect a response.
         queue_event_expect_response(&vcpu_handle, VcpuEvent::Resume, VcpuResponse::Resumed);
@@ -1183,7 +1183,7 @@ pub(crate) mod tests {
 
     #[test]
     fn test_vcpu_save_state_events() {
-        let (vcpu_handle, _vcpu_exit_evt) = vcpu_configured_for_boot();
+        let (vcpu_handle, _vcpu_exit_evt, _) = vcpu_configured_for_boot();
 
         // Queue a Resume event, expect a response.
         queue_event_expect_response(&vcpu_handle, VcpuEvent::Resume, VcpuResponse::Resumed);
@@ -1216,7 +1216,7 @@ pub(crate) mod tests {
 
     #[test]
     fn test_vcpu_dump_cpu_config() {
-        let (vcpu_handle, _) = vcpu_configured_for_boot();
+        let (vcpu_handle, _, _) = vcpu_configured_for_boot();
 
         // Queue a DumpCpuConfig event, expect a DumpedCpuConfig response.
         vcpu_handle