vm: create_vcpu takes u64 argument rust-vmm#123

Changed the passed parameter type from `u8` to `u64`, which the
underlying `ioctl` uses.

Added a missing cap `MaxVcpuId` (It is defined in kvm-bindings for both
arm* and x86* but was missing inside cap.rs. This was required by a test
case.)

Added a test case to assert failure if we pass parameter higher than the
`max_vcpu_id`.

Signed-off-by: Abhijit Gadgil <gabhijit@iitbombay.org>

src/cap.rs

@@ -97,6 +97,7 @@ pub enum Cap {
     PpcSmt = KVM_CAP_PPC_SMT,
     PpcRma = KVM_CAP_PPC_RMA,
     MaxVcpus = KVM_CAP_MAX_VCPUS,
+    MaxVcpuId = KVM_CAP_MAX_VCPU_ID,
     PpcHior = KVM_CAP_PPC_HIOR,
     PpcPapr = KVM_CAP_PPC_PAPR,
     SwTlb = KVM_CAP_SW_TLB,

src/ioctls/vcpu.rs

@@ -1411,7 +1411,7 @@ mod tests {
             assert!(ncpuids <= KVM_MAX_CPUID_ENTRIES);
             let nr_vcpus = kvm.get_nr_vcpus();
             for cpu_idx in 0..nr_vcpus {
-                let vcpu = vm.create_vcpu(cpu_idx as u8).unwrap();
+                let vcpu = vm.create_vcpu(cpu_idx as u64).unwrap();
                 vcpu.set_cpuid2(&cpuid).unwrap();
                 let retrieved_cpuid = vcpu.get_cpuid2(ncpuids).unwrap();
                 // Only check the first few leafs as some (e.g. 13) are reserved.
@@ -1443,7 +1443,7 @@ mod tests {
             assert!(ncpuids <= KVM_MAX_CPUID_ENTRIES);
             let nr_vcpus = kvm.get_nr_vcpus();
             for cpu_idx in 0..nr_vcpus {
-                let vcpu = vm.create_vcpu(cpu_idx as u8).unwrap();
+                let vcpu = vm.create_vcpu(cpu_idx as u64).unwrap();
                 vcpu.set_cpuid2(&cpuid).unwrap();
                 let err = vcpu.get_cpuid2(ncpuids - 1 as usize).err();
                 assert_eq!(err.unwrap().errno(), libc::E2BIG);

src/ioctls/vm.rs

@@ -1021,7 +1021,7 @@ impl VmFd {
     /// let vcpu = vm.create_vcpu(0);
     /// ```
     ///
-    pub fn create_vcpu(&self, id: u8) -> Result<VcpuFd> {
+    pub fn create_vcpu(&self, id: u64) -> Result<VcpuFd> {
         // Safe because we know that vm is a VM fd and we verify the return result.
         #[allow(clippy::cast_lossless)]
         let vcpu_fd = unsafe { ioctl_with_val(&self.vm, KVM_CREATE_VCPU(), id as c_ulong) };
@@ -1799,6 +1799,38 @@ mod tests {
         assert!(vm.set_gsi_routing(&irq_routing).is_ok());
     }
 
+    #[test]
+    fn create_vcpu_different_cpuids() {
+        let kvm = Kvm::new().unwrap();
+        let vm = kvm.create_vm().unwrap();
+
+        // Fails when an arbitrarily large value
+        let err = vm.create_vcpu(65537 as u64).err();
+        assert_eq!(err.unwrap().errno(), libc::EINVAL);
+
+        // Note: We can request up to KVM_MAX_VCPU_ID if it exists or up to KVM_MAX_VCPUS or
+        // NR_CPUS or 4. This is determined by the appropriate capability being present.
+        // We check near boundry conditions `max_vcpus - 1` should succeed but `max_vcpus` as
+        // determined by the appropriate capability should fail.
+        //
+        // Ref: https://www.kernel.org/doc/html/latest/virt/kvm/api.html#kvm-create-vcpu
+        //
+        let mut max_vcpus = vm.check_extension_int(Cap::MaxVcpuId);
+        if max_vcpus == 0 {
+            max_vcpus = vm.check_extension_int(Cap::MaxVcpus);
+        }
+        if max_vcpus == 0 {
+            max_vcpus = vm.check_extension_int(Cap::NrVcpus);
+        }
+        if max_vcpus == 0 {
+            max_vcpus = 4
+        }
+        let vcpu = vm.create_vcpu((max_vcpus - 1) as u64);
+        assert!(vcpu.is_ok());
+        let vcpu_err = vm.create_vcpu(max_vcpus as u64).err();
+        assert_eq!(vcpu_err.unwrap().errno(), libc::EINVAL);
+    }
+
     #[test]
     fn test_check_extension() {
         let kvm = Kvm::new().unwrap();