Building a kernel with the z/VM CP interface

7.1 z/VM guest

Control the build options for the z/VM® CP interface through the kernel configuration menu.

Kernel builders: This information is intended for those who want to build their own kernel. Be aware that both compiling your own kernel or recompiling an existing distribution usually means that you have to maintain your kernel yourself.

Figure 1. Kernel configuration menu options for the z/VM CP interface

 Device Drivers --->
    ...
    Character devices --->
       ...
       --- S/390 character device drivers (depends on S390) ---
       ...
       Support for the z/VM CP interface                      (CONFIG_VMCP)
       └─ Memory in MiB reserved for z/VM CP interface        (CONFIG_VMCP_CMA_SIZE)

CONFIG_VMCP: is required to build a kernel with user space access to CP commands.
CONFIG_VMCP_CMA_SIZE: specifies the default amount of contiguous memory, in MiB, to be reserved for large responses from z/VM CP. CONFIG_VMCP_CMA_SIZE is preset to 4 MiB.
When booting Linux®, the vmcp_cma= kernel parameter can override the value that is set with CONFIG_VMCP_CMA_SIZE.