linux_dsm_epyc7002/Documentation/virtual/kvm/devices/vm.txt

Generic vm interface
====================================

The virtual machine "device" also accepts the ioctls KVM_SET_DEVICE_ATTR,
KVM_GET_DEVICE_ATTR, and KVM_HAS_DEVICE_ATTR. The interface uses the same
struct kvm_device_attr as other devices, but targets VM-wide settings
and controls.

The groups and attributes per virtual machine, if any, are architecture
specific.

1. GROUP: KVM_S390_VM_MEM_CTRL
Architectures: s390

1.1. ATTRIBUTE: KVM_S390_VM_MEM_ENABLE_CMMA
Parameters: none
Returns: -EBUSY if a vcpu is already defined, otherwise 0

Enables Collaborative Memory Management Assist (CMMA) for the virtual machine.

1.2. ATTRIBUTE: KVM_S390_VM_MEM_CLR_CMMA
Parameters: none
Returns: 0

Clear the CMMA status for all guest pages, so any pages the guest marked
as unused are again used any may not be reclaimed by the host.