fix: enforce the minimum cgroupv2 cpu shares to 2

Co-authored-by: dahn <[email protected]>

Author: phsm

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

@@ -320,6 +320,10 @@ public class LibvirtComputingResource extends ServerResourceBase implements Serv
     public static final String WINDOWS_GUEST_CONVERSION_SUPPORTED_CHECK_CMD = "rpm -qa | grep -i virtio-win";
     public static final String UBUNTU_WINDOWS_GUEST_CONVERSION_SUPPORTED_CHECK_CMD = "dpkg -l virtio-win";
     public static final String UBUNTU_NBDKIT_PKG_CHECK_CMD = "dpkg -l nbdkit";
+    
+     // Libvirt < 9.1.0 cgroupv1 CPU shares values range 
+    public static final int LIBVIRT_CGROUPV1_CPU_SHARES_MIN = 2;
+    public static final int LIBVIRT_CGROUPV1_CPU_SHARES_MAX = 262144;		
 
     private String modifyVlanPath;
     private String versionStringPath;
@@ -2796,8 +2800,18 @@ 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 " +
-                    "consider the host limits; the new CPU shares value is [%s].", hostCpuMaxCapacity, requestedCpuShares, updatedCpuShares));
+
+            /**
+             * Libvirt < 9.1.0 enforces the same value range to both cgroupv1 and cgroupv2.
+             * Therefore, if the shares value is determined to be outside of boundaries,
+             * then bring it to the minimum or maximum allowed value.
+             * See: https://github.com/libvirt/libvirt/commit/38af6497610075e5fe386734b87186731d4c17ac
+             */
+            if (updatedCpuShares < LIBVIRT_CGROUPV1_CPU_SHARES_MIN) updatedCpuShares = LIBVIRT_CGROUPV1_CPU_SHARES_MIN;
+            if (updatedCpuShares > LIBVIRT_CGROUPV1_CPU_SHARES_MAX) updatedCpuShares = LIBVIRT_CGROUPV1_CPU_SHARES_MAX;
+
+            LOGGER.debug("This host utilizes cgroupv2 (as the max shares value is [{}]), thus, the VM requested shares of [{}] will be converted to " +
+                    "consider the host limits; the new CPU shares value is [{}].", hostCpuMaxCapacity, requestedCpuShares, updatedCpuShares);
             return updatedCpuShares;
         }
         LOGGER.debug(String.format("This host does not have a maximum CPU shares set; therefore, this host utilizes cgroupv1 and the VM requested CPU shares [%s] will not be " +