[PATCH v5] target/s390x/kvm: Enable adapter interruption suppression again

[Thomas Huth]

The AIS feature has been disabled late in the v2.10 development cycle since
there were some issues with migration (see commit 3f2d07b3b01ea61126b -
"s390x/ais: for 2.10 stable: disable ais facility"). We originally wanted
to enable it again for newer machine types, but apparently we forgot to do
this so far. Let's do it now for the machines that support proper CPU models.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
Signed-off-by: Thomas Huth <address@hidden>
---
 v5: Use cpu_model_allowed() as suggested by David. Seems to work as far
     as I can test it without PCI cards, but ping-pong migration with
     "-cpu host" from/to an older version of QEMU is now not working
     anymore - but I think that's kind of expected since "-cpu host"
     is not migration-safe anyway.

 target/s390x/kvm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index 15260aeb9a..30112e529c 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -365,10 +365,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     /*
      * The migration interface for ais was introduced with kernel 4.13
      * but the capability itself had been active since 4.12. As migration
-     * support is considered necessary let's disable ais in the 2.10
-     * machine.
+     * support is considered necessary, we only try to enable this for
+     * newer machine types if KVM_CAP_S390_AIS_MIGRATION is available.
      */
-    /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
+    if (cpu_model_allowed() && kvm_kernel_irqchip_allowed() &&
+        kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {
+        kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
+    }
 
     kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
     return 0;
-- 
2.18.1