s390x/kvm: passing max memory size to accelerator

With "KVM: s390: Allow userspace to limit guest memory size" KVM is able to
do some optimizations based on the guest memory limit.

The guest memory limit is computed by the initial definition and with the notion of
hotplugged memory.

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Message-Id: <1425570981-40609-3-git-send-email-jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
index 6c4360be65..a585fe3e1c 100644
--- a/target-s390x/kvm.c
+++ b/target-s390x/kvm.c
@@ -122,6 +122,51 @@ static int cap_async_pf;
 
 static void *legacy_s390_alloc(size_t size, uint64_t *align);
 
+static int kvm_s390_supports_mem_limit(KVMState *s)
+{
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_LIMIT_SIZE,
+    };
+
+    return (kvm_vm_ioctl(s, KVM_HAS_DEVICE_ATTR, &attr) == 0);
+}
+
+static int kvm_s390_query_mem_limit(KVMState *s, uint64_t *memory_limit)
+{
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_LIMIT_SIZE,
+        .addr = (uint64_t) memory_limit,
+    };
+
+    return kvm_vm_ioctl(s, KVM_GET_DEVICE_ATTR, &attr);
+}
+
+int kvm_s390_set_mem_limit(KVMState *s, uint64_t new_limit, uint64_t *hw_limit)
+{
+    int rc;
+
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_LIMIT_SIZE,
+        .addr = (uint64_t) &new_limit,
+    };
+
+    if (!kvm_s390_supports_mem_limit(s)) {
+        return 0;
+    }
+
+    rc = kvm_s390_query_mem_limit(s, hw_limit);
+    if (rc) {
+        return rc;
+    } else if (*hw_limit < new_limit) {
+        return -E2BIG;
+    }
+
+    return kvm_vm_ioctl(s, KVM_SET_DEVICE_ATTR, &attr);
+}
+
 static int kvm_s390_check_clear_cmma(KVMState *s)
 {
     struct kvm_device_attr attr = {