3 files changed, 66 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/devices/vm.txt b/Documentation/virtual/kvm/devices/vm.txt
index 562bee6e600b..0d16f96c0eac 100644
--- a/Documentation/virtual/kvm/devices/vm.txt
+++ b/Documentation/virtual/kvm/devices/vm.txt
@@ -8,3 +8,19 @@ 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_CTRL
+Parameters: none
+Returns: -EBUSY if already a vcpus is defined, otherwise 0
+
+Enables CMMA for the virtual machine
+
+1.2. ATTRIBUTE: KVM_S390_VM_CLR_CMMA
+Parameteres: 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.
diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index c003c6a73b1e..e35c79821d29 100644
--- a/arch/s390/include/uapi/asm/kvm.h
+++ b/arch/s390/include/uapi/asm/kvm.h
@@ -54,6 +54,13 @@ struct kvm_s390_io_adapter_req {
         __u64 addr;
 };
 
+/* kvm attr_group  on vm fd */
+#define KVM_S390_VM_MEM_CTRL            0
+
+/* kvm attributes for mem_ctrl */
+#define KVM_S390_VM_MEM_ENABLE_CMMA     0
+#define KVM_S390_VM_MEM_CLR_CMMA        1
+
 /* for KVM_GET_REGS and KVM_SET_REGS */
 struct kvm_regs {
         /* general purpose regs for s390 */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index fc2fe49488c0..fe2396cc0856 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -258,11 +258,43 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
         return r;
 }
 
+static int kvm_s390_mem_control(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+        int ret;
+        unsigned int idx;
+        switch (attr->attr) {
+        case KVM_S390_VM_MEM_ENABLE_CMMA:
+                ret = -EBUSY;
+                mutex_lock(&kvm->lock);
+                if (atomic_read(&kvm->online_vcpus) == 0) {
+                        kvm->arch.use_cmma = 1;
+                        ret = 0;
+                }
+                mutex_unlock(&kvm->lock);
+                break;
+        case KVM_S390_VM_MEM_CLR_CMMA:
+                mutex_lock(&kvm->lock);
+                idx = srcu_read_lock(&kvm->srcu);
+                page_table_reset_pgste(kvm->arch.gmap->mm, 0, TASK_SIZE, false);
+                srcu_read_unlock(&kvm->srcu, idx);
+                mutex_unlock(&kvm->lock);
+                ret = 0;
+                break;
+        default:
+                ret = -ENXIO;
+                break;
+        }
+        return ret;
+}
+
 static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 {
         int ret;
 
         switch (attr->group) {
+        case KVM_S390_VM_MEM_CTRL:
+                ret = kvm_s390_mem_control(kvm, attr);
+                break;
         default:
                 ret = -ENXIO;
                 break;
@@ -281,6 +313,17 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
         int ret;
 
         switch (attr->group) {
+        case KVM_S390_VM_MEM_CTRL:
+                switch (attr->attr) {
+                case KVM_S390_VM_MEM_ENABLE_CMMA:
+                case KVM_S390_VM_MEM_CLR_CMMA:
+                        ret = 0;
+                        break;
+                default:
+                        ret = -ENXIO;
+                        break;
+                }
+                break;
         default:
                 ret = -ENXIO;
                 break;