vcpu: Add wrapper for KVM_GET_ONE_REG.

- add ioctl definition in kvm_ioctls.rs
- implement vcpu.get_one_reg()

Signed-off-by: Andrei Sandu <[email protected]>

Author: sandreim

src/ioctls/vcpu.rs

@@ -972,6 +972,30 @@ impl VcpuFd {
         Ok(())
     }
 
+    /// Returns the value of the specified vCPU register.
+    ///
+    /// The id of the register is encoded as specified in the kernel documentation
+    /// for `KVM_GET_ONE_REG`.
+    ///
+    /// # Arguments
+    ///
+    /// * `reg_id` - ID of the register.
+    ///
+    #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+    pub fn get_one_reg(&self, reg_id: u64) -> Result<u64> {
+        let mut reg_value = 0;
+        let mut onereg = kvm_one_reg {
+            id: reg_id,
+            addr: &mut reg_value as *mut u64 as u64,
+        };
+
+        let ret = unsafe { ioctl_with_mut_ref(self, KVM_GET_ONE_REG(), &mut onereg) };
+        if ret < 0 {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(reg_value)
+    }
+
     /// Triggers the running of the current virtual CPU returning an exit reason.
     ///
     /// See documentation for `KVM_RUN`.
@@ -1623,6 +1647,39 @@ mod tests {
             .expect("Failed to set pstate register");
     }
 
+    #[test]
+    #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+    fn test_get_one_reg() {
+        let kvm = Kvm::new().unwrap();
+        let vm = kvm.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)
+            .expect("Cannot get preferred target");
+        vcpu.vcpu_init(&kvi).expect("Cannot initialize vcpu");
+
+        // PSR (Processor State Register) bits.
+        // Taken from arch/arm64/include/uapi/asm/ptrace.h.
+        const PSR_MODE_EL1H: u64 = 0x0000_0005;
+        const PSR_F_BIT: u64 = 0x0000_0040;
+        const PSR_I_BIT: u64 = 0x0000_0080;
+        const PSR_A_BIT: u64 = 0x0000_0100;
+        const PSR_D_BIT: u64 = 0x0000_0200;
+        const PSTATE_FAULT_BITS_64: u64 =
+            (PSR_MODE_EL1H | PSR_A_BIT | PSR_F_BIT | PSR_I_BIT | PSR_D_BIT);
+        let data: u64 = PSTATE_FAULT_BITS_64;
+        const PSTATE_REG_ID: u64 = 0x6030_0000_0010_0042;
+        vcpu.set_one_reg(PSTATE_REG_ID, data)
+            .expect("Failed to set pstate register");
+
+        assert_eq!(
+            vcpu.get_one_reg(PSTATE_REG_ID)
+                .expect("Failed to get pstate register"),
+            PSTATE_FAULT_BITS_64
+        );
+    }
+
     #[test]
     fn set_kvm_immediate_exit() {
         let kvm = Kvm::new().unwrap();

src/kvm_ioctls.rs

@@ -187,6 +187,8 @@ ioctl_iow_nr!(KVM_ENABLE_CAP, KVMIO, 0xa3, kvm_enable_cap);
 ioctl_iow_nr!(KVM_SIGNAL_MSI, KVMIO, 0xa5, kvm_msi);
 /* Available with KVM_CAP_ONE_REG */
 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+ioctl_iow_nr!(KVM_GET_ONE_REG, KVMIO, 0xab, kvm_one_reg);
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 ioctl_iow_nr!(KVM_SET_ONE_REG, KVMIO, 0xac, kvm_one_reg);
 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 ioctl_iow_nr!(KVM_ARM_VCPU_INIT, KVMIO, 0xae, kvm_vcpu_init);