vmm: Exit VMM event loop after guest shutdown for AArch64

X86 and AArch64 work in different ways to shutdown a VM.
X86 exit VMM event loop through ACPI device;
AArch64 need to exit from CPU loop of a SystemEvent.

Signed-off-by: Michael Zhao <michael.zhao@arm.com>

vmm/src/cpu.rs

@@ -23,6 +23,8 @@ use arch::EntryPoint;
 #[cfg(target_arch = "x86_64")]
 use arch::{CpuidPatch, CpuidReg};
 use devices::{interrupt_controller::InterruptController, BusDevice};
+#[cfg(target_arch = "aarch64")]
+use kvm_bindings::KVM_SYSTEM_EVENT_SHUTDOWN;
 #[cfg(target_arch = "x86_64")]
 use kvm_bindings::{
     kvm_fpu, kvm_lapic_state, kvm_mp_state, kvm_regs, kvm_sregs, kvm_vcpu_events, kvm_xcrs,
@@ -368,6 +370,20 @@ impl Vcpu {
                     // Triple fault to trigger a reboot
                     Ok(false)
                 }
+                #[cfg(target_arch = "aarch64")]
+                VcpuExit::SystemEvent(event_type, flags) => {
+                    // On Aarch64, when the VM is shutdown, run() returns
+                    // VcpuExit::SystemEvent with reason KVM_SYSTEM_EVENT_SHUTDOWN
+                    if event_type == KVM_SYSTEM_EVENT_SHUTDOWN {
+                        Ok(false)
+                    } else {
+                        error!(
+                            "Unexpected system event with type 0x{:x}, flags 0x{:x}",
+                            event_type, flags
+                        );
+                        Err(Error::VcpuUnhandledKvmExit)
+                    }
+                }
                 r => {
                     error!("Unexpected exit reason on vcpu run: {:?}", r);
                     Err(Error::VcpuUnhandledKvmExit)

vmm/src/lib.rs

@@ -365,7 +365,8 @@ impl Vmm {
         #[cfg(not(feature = "acpi"))]
         {
             if self.vm.is_some() {
-                return self.vm_shutdown();
+                self.exit_evt.write(1).unwrap();
+                return Ok(());
             }
         }