Re: [libvirt PATCH 3/3] qemu_capabilities: Disable CPU models on old s390 machine types

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It does what it is supposed to do even so version checking is not really nice but not spending the effort to design a new qom interface is OK.

@Christian Ehrhardt: I guess you need to add the ubuntu effected machine type(s) to s390HostPassthroughOnlyMachines as well as add an adjusted test like in patch 2 of this series for ubuntu.

Reviewed-by: Boris Fiuczynski <fiuczy@xxxxxxxxxxxxx>

On 2/6/20 11:24 AM, Jiri Denemark wrote:
Starting a KVM domain on s390 with old machine type (such as
s390-ccw-virtio-2.5) and without any guest CPU model configured fails
with

     CPU models are not available: KVM doesn't support CPU models

QEMU error. This is cause by libvirt using host-model CPU as the default
CPU based on QEMU reporting "host" CPU model as being the default one
(see commit v5.9.0-402-g24d8202294: qemu: Use host-model CPU on s390 by
default). However, even though both QEMU and KVM support CPU models on
s390 and QEMU can give us the host-model CPU, we can't use it with old
machine types which only support -cpu host.

https://bugzilla.redhat.com/show_bug.cgi?id=1795651

Reported-by: Christian Ehrhardt <paelzer@xxxxxxxxx>
Signed-off-by: Jiri Denemark <jdenemar@xxxxxxxxxx>
---
  src/qemu/qemu_capabilities.c                  | 19 ++++++++++++++++++-
  ...t-cpu-kvm-ccw-virtio-2.7.s390x-latest.args |  4 +---
  ...lt-cpu-kvm-ccw-virtio-2.7.s390x-latest.xml |  2 +-
  3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 162e49e2d4..dd2311cfa9 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -2274,16 +2274,33 @@ virQEMUCapsIsVirtTypeSupported(virQEMUCapsPtr qemuCaps,
      return false;
  }
+const char *s390HostPassthroughOnlyMachines[] = {
+    "s390-ccw-virtio-2.4",
+    "s390-ccw-virtio-2.5",
+    "s390-ccw-virtio-2.6",
+    "s390-ccw-virtio-2.7",
+    NULL
+};
bool
  virQEMUCapsIsCPUModeSupported(virQEMUCapsPtr qemuCaps,
                                virArch hostarch,
                                virDomainVirtType type,
                                virCPUMode mode,
-                              const char *machineType G_GNUC_UNUSED)
+                              const char *machineType)
  {
      qemuMonitorCPUDefsPtr cpus;
+ /* CPU models (except for "host") are not supported by QEMU for on s390
+     * KVM domains with old machine types regardless on QEMU version. */
+    if (ARCH_IS_S390(qemuCaps->arch) &&
+        type == VIR_DOMAIN_VIRT_KVM &&
+        mode != VIR_CPU_MODE_HOST_PASSTHROUGH &&
+        machineType &&
+        g_strv_contains(s390HostPassthroughOnlyMachines, machineType)) {
+        return false;
+    }
+
      switch (mode) {
      case VIR_CPU_MODE_HOST_PASSTHROUGH:
          return type == VIR_DOMAIN_VIRT_KVM &&
diff --git a/tests/qemuxml2argvdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.args b/tests/qemuxml2argvdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.args
index 8c25a01e74..0c2567df6c 100644
--- a/tests/qemuxml2argvdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.args
+++ b/tests/qemuxml2argvdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.args
@@ -13,9 +13,7 @@ QEMU_AUDIO_DRV=none \
  -object secret,id=masterKey0,format=raw,\
  file=/tmp/lib/domain--1-test/master-key.aes \
  -machine s390-ccw-virtio-2.7,accel=kvm,usb=off,dump-guest-core=off \
--cpu z13.2-base,aen=on,aefsi=on,msa5=on,msa4=on,msa3=on,msa2=on,msa1=on,\
-sthyi=on,edat=on,ri=on,edat2=on,vx=on,ipter=on,ap=on,esop=on,apft=on,apqci=on,\
-cte=on,bpb=on,ppa15=on,zpci=on,sea_esop2=on,te=on,cmm=on \
+-cpu host \
  -m 256 \
  -overcommit mem-lock=off \
  -smp 1,sockets=1,cores=1,threads=1 \
diff --git a/tests/qemuxml2xmloutdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.xml b/tests/qemuxml2xmloutdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.xml
index 56fd22b6e5..8799584c11 100644
--- a/tests/qemuxml2xmloutdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.xml
+++ b/tests/qemuxml2xmloutdata/s390-default-cpu-kvm-ccw-virtio-2.7.s390x-latest.xml
@@ -8,7 +8,7 @@
      <type arch='s390x' machine='s390-ccw-virtio-2.7'>hvm</type>
      <boot dev='hd'/>
    </os>
-  <cpu mode='host-model' check='partial'/>
+  <cpu mode='host-passthrough' check='none'/>
    <clock offset='utc'/>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>



--
Mit freundlichen Grüßen/Kind regards
   Boris Fiuczynski

IBM Deutschland Research & Development GmbH
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Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
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