fix: enforce the minimum cgroupv2 cpu shares to 2

Author: phsm

plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java

@@ -2796,7 +2796,15 @@ public int calculateCpuShares(VirtualMachineTO vmTO) {
 
         if (hostCpuMaxCapacity > 0) {
             int updatedCpuShares = (int) Math.ceil((requestedCpuShares * CGROUP_V2_UPPER_LIMIT) / (double) hostCpuMaxCapacity);
-            LOGGER.debug(String.format("This host utilizes cgroupv2 (as the max shares value is [%s]), thus, the VM requested shares of [%s] will be converted to " +
+
+            /**
+             * Libvirt < 9.1.0 enforces the range [2, 262144] to both cgroupv1 and cgroupv2.
+             * Therefore, if the shares value is determined to be < 2, then raise it to 2 to fit into the constraint.
+             * See: https://github.com/libvirt/libvirt/commit/38af6497610075e5fe386734b87186731d4c17ac
+             */
+            if (updatedCpuShares < 2) updatedCpuShares = 2;
+
+            logger.debug(String.format("This host utilizes cgroupv2 (as the max shares value is [%s]), thus, the VM requested shares of [%s] will be converted to " +
                     "consider the host limits; the new CPU shares value is [%s].", hostCpuMaxCapacity, requestedCpuShares, updatedCpuShares));
             return updatedCpuShares;
         }