Create an AArch64 specific create_vm

Not all AArch64 platforms support IPAs up to 40 bits. When KVM
supports Cap::ArmVmIPASize it's better to get the IPA size from
the host and use that when creating the VM, which may avoid
unnecessary VM creation failures. Additionally, when 40 is
selected with the value 0, which means use the default, some
versions of KVM will skip a check resulting in a difficult to
debug fail. We must still use 0 when KVM only supports the
legacy fixed 40 bit IPA.

Signed-off-by: Andrew Jones <drjones@redhat.com>

Author: Andrew Jones

src/ioctls/system.rs

@@ -381,10 +381,36 @@ impl Kvm {
     /// assert!(vm.run_size() == kvm.get_vcpu_mmap_size().unwrap());
     /// ```
     ///
+    #[cfg(not(any(target_arch = "aarch64")))]
     pub fn create_vm(&self) -> Result<VmFd> {
         self.create_vm_with_type(0) // Create using default VM type
     }
 
+    /// AArch64 specific create_vm to create a VM fd using the KVM fd using the host's maximum IPA size.
+    ///
+    /// See the arm64 section of KVM documentation for `KVM_CREATE_VM`.
+    /// A call to this function will also initialize the size of the vcpu mmap area using the
+    /// `KVM_GET_VCPU_MMAP_SIZE` ioctl.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use kvm_ioctls::Kvm;
+    /// let kvm = Kvm::new().unwrap();
+    /// let vm = kvm.create_vm().unwrap();
+    /// // Check that the VM mmap size is the same reported by `KVM_GET_VCPU_MMAP_SIZE`.
+    /// assert!(vm.run_size() == kvm.get_vcpu_mmap_size().unwrap());
+    /// ```
+    ///
+    #[cfg(any(target_arch = "aarch64"))]
+    pub fn create_vm(&self) -> Result<VmFd> {
+        let mut ipa_size = 0; // Create using default VM type
+        if self.check_extension(Cap::ArmVmIPASize) {
+            ipa_size = self.get_host_ipa_limit();
+        }
+        self.create_vm_with_type(ipa_size as u64)
+    }
+
     /// AArch64 specific function to create a VM fd using the KVM fd with flexible IPA size.
     ///
     /// See the arm64 section of KVM documentation for `KVM_CREATE_VM`.