[Qemu-devel] [RFC 22/28] s390x/kvm: let the CPU model control CMM(A)

[David Hildenbrand <dahi@linux.vnet.ibm.com>]

Starting with recent kernels, if the cmma attributes are available, we
actually have hardware support. Enabling CMMA then means providing the
guest VCPU with CMM, therefore enabling its CMM facility.

Let's not blindly enable CMM anymore but let's control it using CPU models.
For disabled CPU models, CMMA will continue to always get enabled.

Also enable it in the applicable default models.

Please note that CMM doesn't work with hugetlbfs, therefore we will
warn the user and keep it disabled. Migrating from/to a hugetlbfs
configuration works, as it will be disabled on both sides.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 target-s390x/gen-features.c |  1 +
 target-s390x/kvm.c          | 47 ++++++++++++++++++++++++++++++++++-----------
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/target-s390x/gen-features.c b/target-s390x/gen-features.c
index d4f4b29..52d46dc 100644
--- a/target-s390x/gen-features.c
+++ b/target-s390x/gen-features.c
@@ -371,6 +371,7 @@ static uint16_t full_GEN13_GA1[] = {
 #define default_GEN8_GA5 EmptyFeat
 static uint16_t default_GEN9_GA1[] = {
     S390_FEAT_GROUP_MSA_EXT_1,
+    S390_FEAT_CMM,
 };
 #define default_GEN9_GA2 EmptyFeat
 #define default_GEN9_GA3 EmptyFeat
diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
index a4f5762..dd2abec 100644
--- a/target-s390x/kvm.c
+++ b/target-s390x/kvm.c
@@ -174,6 +174,18 @@ int kvm_s390_set_mem_limit(KVMState *s, uint64_t new_limit, uint64_t *hw_limit)
     return kvm_vm_ioctl(s, KVM_SET_DEVICE_ATTR, &attr);
 }
 
+static bool kvm_s390_cmma_available(void)
+{
+    static bool initialized, value;
+
+    if (!initialized) {
+        initialized = true;
+        value = kvm_vm_check_mem_attr(kvm_state, KVM_S390_VM_MEM_ENABLE_CMMA) &&
+                kvm_vm_check_mem_attr(kvm_state, KVM_S390_VM_MEM_CLR_CMMA);
+    }
+    return value;
+}
+
 void kvm_s390_cmma_reset(void)
 {
     int rc;
@@ -182,11 +194,15 @@ void kvm_s390_cmma_reset(void)
         .attr = KVM_S390_VM_MEM_CLR_CMMA,
     };
 
+    if (!mem_path || !kvm_s390_cmma_available()) {
+        return;
+    }
+
     rc = kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
     trace_kvm_clear_cmma(rc);
 }
 
-static void kvm_s390_enable_cmma(KVMState *s)
+static void kvm_s390_enable_cmma(void)
 {
     int rc;
     struct kvm_device_attr attr = {
@@ -194,12 +210,7 @@ static void kvm_s390_enable_cmma(KVMState *s)
         .attr = KVM_S390_VM_MEM_ENABLE_CMMA,
     };
 
-    if (!kvm_vm_check_mem_attr(s, KVM_S390_VM_MEM_ENABLE_CMMA) ||
-        !kvm_vm_check_mem_attr(s, KVM_S390_VM_MEM_CLR_CMMA)) {
-        return;
-    }
-
-    rc = kvm_vm_ioctl(s, KVM_SET_DEVICE_ATTR, &attr);
+    rc = kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
     trace_kvm_enable_cmma(rc);
 }
 
@@ -259,10 +270,6 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
     cap_s390_irq = kvm_check_extension(s, KVM_CAP_S390_INJECT_IRQ);
 
-    if (!mem_path) {
-        kvm_s390_enable_cmma(s);
-    }
-
     if (!kvm_check_extension(s, KVM_CAP_S390_GMAP)
         || !kvm_check_extension(s, KVM_CAP_S390_COW)) {
         phys_mem_set_alloc(legacy_s390_alloc);
@@ -2509,6 +2516,11 @@ void kvm_s390_get_host_cpu_model(S390CPUModel *model, Error **errp)
         return;
     }
 
+    /* with cpu model support, CMM is only indicated if really available */
+    if (kvm_s390_cmma_available()) {
+        set_bit(S390_FEAT_CMM, model->features);
+    }
+
     if (s390_known_cpu_type(cpu_type)) {
         /* we want the exact model, even if some features are missing */
         model->def = s390_find_cpu_def(cpu_type, ibc_gen(unblocked_ibc),
@@ -2541,6 +2553,10 @@ void kvm_s390_apply_cpu_model(const S390CPUModel *model, Error **errp)
     int rc;
 
     if (!model) {
+        /* compatibility handling if cpu models are disabled */
+        if (kvm_s390_cmma_available() && !mem_path) {
+            kvm_s390_enable_cmma();
+        }
         return;
     }
     if (!kvm_s390_cpu_models_supported()) {
@@ -2569,4 +2585,13 @@ void kvm_s390_apply_cpu_model(const S390CPUModel *model, Error **errp)
         error_setg(errp, "KVM: Error configuring CPU subfunctions: %d", rc);
         return;
     }
+    /* enable CMM via CMMA - disable on hugetlbfs */
+    if (test_bit(S390_FEAT_CMM, model->features)) {
+        if (mem_path) {
+            error_report("Warning: CMM will not be enabled because it is not "
+                         "compatible to hugetlbfs.");
+        } else {
+            kvm_s390_enable_cmma();
+        }
+    }
 }
-- 
2.6.6