vmm: cpu: Notify guest OS that it should offline vCPUs

Allow the resizing of the number of vCPUs to less than the current
active vCPUs. This does not currently remove them from the system but
the kernel will take them offline.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/cpu.rs

@@ -389,6 +389,7 @@ pub struct CpuManager {
 
 const CPU_ENABLE_FLAG: usize = 0;
 const CPU_INSERTING_FLAG: usize = 1;
+const CPU_REMOVING_FLAG: usize = 2;
 
 const CPU_STATUS_OFFSET: u64 = 4;
 const CPU_SELECTION_OFFSET: u64 = 0;
@@ -405,6 +406,9 @@ impl BusDevice for CpuManager {
                     if state.inserting {
                         data[0] |= 1 << CPU_INSERTING_FLAG;
                     }
+                    if state.removing {
+                        data[0] |= 1 << CPU_REMOVING_FLAG;
+                    }
                 }
             }
             _ => {
@@ -429,6 +433,11 @@ impl BusDevice for CpuManager {
                 {
                     state.inserting = false;
                 }
+                // Ditto for removal
+                if (data[0] & (1 << CPU_REMOVING_FLAG) == 1 << CPU_REMOVING_FLAG) && state.removing
+                {
+                    state.removing = false;
+                }
             }
             _ => {
                 warn!(
@@ -443,6 +452,7 @@ impl BusDevice for CpuManager {
 #[derive(Default)]
 struct VcpuState {
     inserting: bool,
+    removing: bool,
     handle: Option<thread::JoinHandle<()>>,
 }
 
@@ -621,13 +631,27 @@ impl CpuManager {
         Ok(())
     }
 
+    fn mark_vcpus_for_removal(&mut self, desired_vcpus: u8) -> Result<()> {
+        // Mark vCPUs for removal, actual removal happens on ejection
+        for cpu_id in desired_vcpus..self.present_vcpus() {
+            self.vcpu_states[usize::from(cpu_id)].removing = true;
+        }
+        Ok(())
+    }
+
     // Starts all the vCPUs that the VM is booting with. Blocks until all vCPUs are running.
     pub fn start_boot_vcpus(&mut self, entry_addr: GuestAddress) -> Result<()> {
         self.activate_vcpus(self.boot_vcpus(), Some(entry_addr))
     }
 
     pub fn resize(&mut self, desired_vcpus: u8) -> Result<()> {
-        self.activate_vcpus(desired_vcpus, None)
+        if desired_vcpus > self.present_vcpus() {
+            self.activate_vcpus(desired_vcpus, None)?;
+        } else if desired_vcpus < self.present_vcpus() {
+            self.mark_vcpus_for_removal(desired_vcpus)?;
+        }
+
+        Ok(())
     }
 
     pub fn shutdown(&mut self) -> Result<()> {
@@ -857,6 +881,22 @@ impl Aml for CPUMethods {
                                     ),
                                 ],
                             ),
+                            // Check if CRMV bit is set
+                            &aml::If::new(
+                                &aml::Equal::new(&aml::Path::new("\\_SB_.PRES.CRMV"), &aml::ONE),
+                                // Notify device if it is (with the eject constant 0x3)
+                                vec![
+                                    &aml::MethodCall::new(
+                                        "CTFY".into(),
+                                        vec![&aml::Local(0), &3u8],
+                                    ),
+                                    // Reset CRMV bit
+                                    &aml::Store::new(
+                                        &aml::Path::new("\\_SB_.PRES.CRMV"),
+                                        &aml::ONE,
+                                    ),
+                                ],
+                            ),
                             &aml::Add::new(&aml::Local(0), &aml::Local(0), &aml::ONE),
                         ],
                     ),