qemu: command: Support arm 32-on-64 KVM with -cpu aarch64=off

qemu 2.3.0 added the -cpu host,aarch64=off option, which allows using
qemu-system-aarch64 KVM to run armv7l VMs.

Add a capabilities check for it, wire it up in qemu_command, and test
the command line generation.

src/qemu/qemu_capabilities.c

@@ -284,6 +284,7 @@ VIR_ENUM_IMPL(virQEMUCaps, QEMU_CAPS_LAST,
               "aes-key-wrap",
               "dea-key-wrap",
               "pci-serial",
+              "aarch64-off",
     );
 
 
@@ -3283,6 +3284,12 @@ virQEMUCapsInitQMPMonitor(virQEMUCapsPtr qemuCaps,
     if (qemuCaps->version >= 2002000)
         virQEMUCapsSet(qemuCaps, QEMU_CAPS_MACHINE_VMPORT_OPT);
 
+    /* -cpu ...,aarch64=off supported in v2.3.0 and onwards. But it
+       isn't detectable via qmp at this point */
+    if (qemuCaps->arch == VIR_ARCH_AARCH64 &&
+        qemuCaps->version >= 2003000)
+        virQEMUCapsSet(qemuCaps, QEMU_CAPS_CPU_AARCH64_OFF);
+
     if (virQEMUCapsProbeQMPCommands(qemuCaps, mon) < 0)
         goto cleanup;
     if (virQEMUCapsProbeQMPEvents(qemuCaps, mon) < 0)

src/qemu/qemu_capabilities.h

@@ -228,6 +228,7 @@ typedef enum {
     QEMU_CAPS_AES_KEY_WRAP       = 186, /* -machine aes_key_wrap */
     QEMU_CAPS_DEA_KEY_WRAP       = 187, /* -machine dea_key_wrap */
     QEMU_CAPS_DEVICE_PCI_SERIAL  = 188, /* -device pci-serial */
+    QEMU_CAPS_CPU_AARCH64_OFF    = 189, /* -cpu ...,aarch64=off */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 } virQEMUCapsFlags;

src/qemu/qemu_command.c

@@ -7021,6 +7021,19 @@ qemuBuildCpuModelArgStr(virQEMUDriverPtr driver,
         }
         virBufferAddLit(buf, "host");
 
+        if (def->os.arch == VIR_ARCH_ARMV7L &&
+            host->arch == VIR_ARCH_AARCH64) {
+            if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CPU_AARCH64_OFF)) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("QEMU binary does not support CPU "
+                                 "host-passthrough for armv7l on "
+                                 "aarch64 host"));
+                goto cleanup;
+            }
+
+            virBufferAddLit(buf, ",aarch64=off");
+        }
+
         if (ARCH_IS_PPC64(def->os.arch) &&
             cpu->mode == VIR_CPU_MODE_HOST_MODEL &&
             def->cpu->model != NULL) {

tests/qemuxml2argvdata/qemuxml2argv-aarch64-kvm-32-on-64.args

@@ -0,0 +1,10 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-aarch64 -S -M virt -cpu host,aarch64=off -m 1024 -smp 1 \
+-nographic -nodefconfig -nodefaults \
+-monitor unix:/tmp/test-monitor,server,nowait \
+-boot c -kernel /arm.kernel -initrd /arm.initrd \
+-append 'console=ttyAMA0,115200n8 rw root=/dev/vda rootwait physmap.enabled=0' \
+-usb -drive file=/arm.raw,if=none,id=drive-virtio-disk0 \
+-device virtio-blk-device,drive=drive-virtio-disk0,id=virtio-disk0 \
+-device virtio-net-device,vlan=0,id=net0,mac=52:54:00:09:a4:37 \
+-net user,vlan=0,name=hostnet0 -serial pty

tests/qemuxml2argvdata/qemuxml2argv-aarch64-kvm-32-on-64.xml

@@ -0,0 +1,35 @@
+<domain type="kvm">
+  <name>armtest</name>
+  <uuid>496d7ea8-9739-544b-4ebd-ef08be936e6a</uuid>
+  <memory>1048576</memory>
+  <currentMemory>1048576</currentMemory>
+  <vcpu>1</vcpu>
+  <os>
+    <type arch="armv7l" machine="virt">hvm</type>
+    <kernel>/arm.kernel</kernel>
+    <initrd>/arm.initrd</initrd>
+    <cmdline>console=ttyAMA0,115200n8 rw root=/dev/vda rootwait physmap.enabled=0</cmdline>
+  </os>
+  <features>
+    <acpi/>
+    <apic/>
+    <pae/>
+  </features>
+  <cpu mode='host-passthrough'/>
+  <clock offset="utc"/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-aarch64</emulator>
+    <disk type='file' device='disk'>
+      <source file='/arm.raw'/>
+      <target dev='vda' bus='virtio'/>
+    </disk>
+    <interface type='user'>
+      <mac address='52:54:00:09:a4:37'/>
+      <model type='virtio'/>
+    </interface>
+    <console type='pty'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -1552,6 +1552,15 @@ mymain(void)
     DO_TEST("aarch64-gic", QEMU_CAPS_DEVICE, QEMU_CAPS_DRIVE,
             QEMU_CAPS_KVM);
 
+    driver.caps->host.cpu->arch = VIR_ARCH_AARCH64;
+    DO_TEST("aarch64-kvm-32-on-64", QEMU_CAPS_DEVICE, QEMU_CAPS_DRIVE,
+            QEMU_CAPS_NODEFCONFIG, QEMU_CAPS_DEVICE_VIRTIO_MMIO,
+            QEMU_CAPS_KVM, QEMU_CAPS_CPU_HOST, QEMU_CAPS_CPU_AARCH64_OFF);
+    DO_TEST_FAILURE("aarch64-kvm-32-on-64", QEMU_CAPS_DEVICE, QEMU_CAPS_DRIVE,
+            QEMU_CAPS_NODEFCONFIG, QEMU_CAPS_DEVICE_VIRTIO_MMIO,
+            QEMU_CAPS_KVM, QEMU_CAPS_CPU_HOST);
+    driver.caps->host.cpu->arch = cpuDefault->arch;
+
     DO_TEST("kvm-pit-device", QEMU_CAPS_KVM_PIT_TICK_POLICY);
     DO_TEST("kvm-pit-delay", QEMU_CAPS_NO_KVM_PIT);
     DO_TEST("kvm-pit-device", QEMU_CAPS_NO_KVM_PIT,