refactor: stop caching mpidr in struct KvmVcpu

This cached field was only accessed precisely once, so the getter might
as well compute it instead. While we're at it, merge the getting with
the free-standing computation function.

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

Author: roypat

src/vmm/src/arch/aarch64/mod.rs

@@ -98,7 +98,8 @@ pub fn configure_system_for_boot(
     let vcpu_mpidr = vcpus
         .iter_mut()
         .map(|cpu| cpu.kvm_vcpu.get_mpidr())
-        .collect();
+        .collect::<Result<Vec<_>, _>>()
+        .map_err(KvmVcpuError::ConfigureRegisters)?;
     let cmdline = boot_cmdline
         .as_cstring()
         .expect("Cannot create cstring from cmdline string");

src/vmm/src/arch/aarch64/vcpu.rs

@@ -140,16 +140,6 @@ pub fn setup_boot_regs(
     Ok(())
 }
 
-/// Read the MPIDR - Multiprocessor Affinity Register.
-pub fn get_mpidr(vcpufd: &VcpuFd) -> Result<u64, VcpuArchError> {
-    // MPIDR register is 64 bit wide on aarch64
-    let mut mpidr = [0_u8; 8];
-    match vcpufd.get_one_reg(MPIDR_EL1, &mut mpidr) {
-        Err(err) => Err(VcpuArchError::GetOneReg(MPIDR_EL1, err)),
-        Ok(_) => Ok(u64::from_le_bytes(mpidr)),
-    }
-}
-
 /// Saves the states of the system registers into `state`.
 ///
 /// # Arguments
@@ -277,7 +267,6 @@ pub struct KvmVcpu {
     pub fd: VcpuFd,
     /// Vcpu peripherals, such as buses
     pub peripherals: Peripherals,
-    mpidr: u64,
     kvi: kvm_vcpu_init,
 }
 
@@ -311,14 +300,18 @@ impl KvmVcpu {
             index,
             fd: kvm_vcpu,
             peripherals: Default::default(),
-            mpidr: 0,
             kvi,
         })
     }
 
-    /// Gets the MPIDR register value.
-    pub fn get_mpidr(&self) -> u64 {
-        self.mpidr
+    /// Read the MPIDR - Multiprocessor Affinity Register.
+    pub fn get_mpidr(&self) -> Result<u64, VcpuArchError> {
+        // MPIDR register is 64 bit wide on aarch64
+        let mut mpidr = [0_u8; 8];
+        match self.fd.get_one_reg(MPIDR_EL1, &mut mpidr) {
+            Err(err) => Err(VcpuArchError::GetOneReg(MPIDR_EL1, err)),
+            Ok(_) => Ok(u64::from_le_bytes(mpidr)),
+        }
     }
 
     /// Configures an aarch64 specific vcpu for booting Linux.
@@ -351,8 +344,6 @@ impl KvmVcpu {
         )
         .map_err(KvmVcpuError::ConfigureRegisters)?;
 
-        self.mpidr = get_mpidr(&self.fd).map_err(KvmVcpuError::ConfigureRegisters)?;
-
         Ok(())
     }
 
@@ -393,7 +384,7 @@ impl KvmVcpu {
             ..Default::default()
         };
         get_all_registers(&self.fd, &mut state.regs).map_err(KvmVcpuError::SaveState)?;
-        state.mpidr = get_mpidr(&self.fd).map_err(KvmVcpuError::SaveState)?;
+        state.mpidr = self.get_mpidr().map_err(KvmVcpuError::SaveState)?;
 
         state.kvi = self.kvi;
         // We don't save power off state in a snapshot, because
@@ -757,21 +748,17 @@ mod tests {
 
     #[test]
     fn test_read_mpidr() {
-        let kvm = Kvm::new(vec![]).unwrap();
-        let vm = kvm.fd.create_vm().unwrap();
-        let vcpu = vm.create_vcpu(0).unwrap();
-        let mut kvi: kvm_bindings::kvm_vcpu_init = kvm_bindings::kvm_vcpu_init::default();
-        vm.get_preferred_target(&mut kvi).unwrap();
+        let (_, _, vcpu, _) = setup_vcpu(0x10000);
 
         // Must fail when vcpu is not initialized yet.
-        let res = get_mpidr(&vcpu);
+        let res = vcpu.get_mpidr();
         assert!(matches!(
             res.unwrap_err(),
             VcpuArchError::GetOneReg(MPIDR_EL1, _)
         ));
 
-        vcpu.vcpu_init(&kvi).unwrap();
-        assert_eq!(get_mpidr(&vcpu).unwrap(), 0x8000_0000);
+        vcpu.init_vcpu().unwrap();
+        assert_eq!(vcpu.get_mpidr().unwrap(), 0x8000_0000);
     }
 
     #[test]