cpu: Prefer maximum mode for many emulated guests

The actual default CPU at the QEMU level is often a relatively
poor choice, which is stuck with just baseline functionality
and can sometimes not run modern guests at all.

Whenever possible, prefer maximum mode for a much nicer out of
the box experience.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>

tests/data/cli/compare/virt-install-aarch64-machdefault.xml

@@ -18,9 +18,7 @@
   <features>
     <acpi/>
   </features>
-  <cpu mode="custom" match="exact">
+  <cpu mode="maximum"/>
-    <model>cortex-a57</model>
-  </cpu>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-aarch64</emulator>

tests/data/cli/compare/virt-install-aarch64-machvirt.xml

@@ -18,9 +18,7 @@
   <features>
     <acpi/>
   </features>
-  <cpu mode="custom" match="exact">
+  <cpu mode="maximum"/>
-    <model>cortex-a57</model>
-  </cpu>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-aarch64</emulator>

tests/data/cli/compare/virt-install-arm-defaultmach-f20.xml

@@ -15,6 +15,7 @@
     <initrd>/f19-arm.initrd</initrd>
     <cmdline>foo</cmdline>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-arm</emulator>

tests/data/cli/compare/virt-install-arm-virt-f20.xml

@@ -15,6 +15,7 @@
     <initrd>/f19-arm.initrd</initrd>
     <cmdline>console=ttyAMA0,1234 rw root=/dev/vda3</cmdline>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-arm</emulator>

tests/data/cli/compare/virt-install-riscv64-cdrom.xml

@@ -14,6 +14,7 @@
     <boot dev="cdrom"/>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>
@@ -92,6 +93,7 @@
     <type arch="riscv64" machine="virt">hvm</type>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/data/cli/compare/virt-install-riscv64-cloud-init.xml

@@ -12,6 +12,7 @@
   <os firmware="efi">
     <type arch="riscv64" machine="virt">hvm</type>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>
@@ -87,6 +88,7 @@
     <type arch="riscv64" machine="virt">hvm</type>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/data/cli/compare/virt-install-riscv64-graphics.xml

@@ -13,6 +13,7 @@
     <type arch="riscv64" machine="virt">hvm</type>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/data/cli/compare/virt-install-riscv64-headless.xml

@@ -13,6 +13,7 @@
     <type arch="riscv64" machine="virt">hvm</type>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/data/cli/compare/virt-install-riscv64-kernel-boot.xml

@@ -15,6 +15,7 @@
     <initrd>/initrd.img</initrd>
     <cmdline>root=/dev/vda2</cmdline>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/data/cli/compare/virt-install-riscv64-unattended.xml

@@ -12,6 +12,7 @@
   <os firmware="efi">
     <type arch="riscv64" machine="virt">hvm</type>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>
@@ -90,6 +91,7 @@
     <type arch="riscv64" machine="virt">hvm</type>
     <boot dev="hd"/>
   </os>
+  <cpu mode="maximum"/>
   <clock offset="utc"/>
   <devices>
     <emulator>/usr/bin/qemu-system-riscv64</emulator>

tests/test_cli.py

@@ -1247,7 +1247,7 @@ c.add_compare("--connect %(URI-KVM-ARMV7L)s --disk %(EXISTIMG1)s --import --os-v
 
 c.add_valid("--arch aarch64 --osinfo fedora19 --nodisks --pxe --connect " + utils.URIs.kvm_x86_nodomcaps, grep="Libvirt version does not support UEFI")  # attempt to default to aarch64 UEFI, but it fails, but should only print warnings
 c.add_invalid("--arch aarch64 --nodisks --pxe --connect " + utils.URIs.kvm_x86, grep="OS name is required")  # catch missing osinfo for non-x86
-c.add_compare("--arch aarch64 --osinfo fedora19 --machine virt --boot kernel=/f19-arm.kernel,initrd=/f19-arm.initrd,kernel_args=\"console=ttyAMA0,1234 rw root=/dev/vda3\" --disk %(EXISTIMG1)s", "aarch64-machvirt")
+c.add_compare("--arch aarch64 --osinfo fedora19 --machine virt --cpu default --boot kernel=/f19-arm.kernel,initrd=/f19-arm.initrd,kernel_args=\"console=ttyAMA0,1234 rw root=/dev/vda3\" --disk %(EXISTIMG1)s", "aarch64-machvirt")
 c.add_compare("--arch aarch64 --osinfo fedora19 --boot kernel=/f19-arm.kernel,initrd=/f19-arm.initrd,kernel_args=\"console=ttyAMA0,1234 rw root=/dev/vda3\" --disk %(EXISTIMG1)s", "aarch64-machdefault")
 c.add_compare("--arch aarch64 --cdrom %(ISO-F26-NETINST)s --boot loader=CODE.fd,nvram.template=VARS.fd --disk %(EXISTIMG1)s --cpu none --events on_crash=preserve,on_reboot=destroy,on_poweroff=restart", "aarch64-cdrom")  # cdrom test, but also --cpu none override, --events override, and headless
 c.add_compare("--connect %(URI-KVM-AARCH64)s --disk %(EXISTIMG1)s --import --os-variant fedora21 --panic default --graphics vnc", "aarch64-kvm-import")  # --import test, but also test --panic no-op, and --graphics

virtinst/domain/cpu.py

@@ -275,11 +275,26 @@ class DomainCpu(XMLBuilder):
                      SPECIAL_MODE_HOST_PASSTHROUGH, SPECIAL_MODE_MAXIMUM,
                      SPECIAL_MODE_CLEAR, SPECIAL_MODE_APP_DEFAULT]
 
+    def _should_use_maximum_cpu_mode(self, guest, domcaps):
+        if (domcaps.supports_maximum_cpu_mode() and
+            guest.type == "qemu" and
+            (guest.os.is_x86() or
+             guest.os.is_arm_machvirt() or
+             guest.os.is_riscv_virt() or
+             guest.os.is_loongarch64())):
+            return True
+
+        return False
+
     def _get_app_default_mode(self, guest):
         # Depending on if libvirt+qemu is new enough, we prefer
         # host-passthrough, then host-model, and finally host-model-only
+        # Emulated guests use maximum mode if available
         domcaps = guest.lookup_domcaps()
 
+        if (self._should_use_maximum_cpu_mode(guest, domcaps)):
+            return self.SPECIAL_MODE_MAXIMUM
+
         if domcaps.supports_safe_host_passthrough():
             return self.SPECIAL_MODE_HOST_PASSTHROUGH
 
@@ -460,9 +475,12 @@ class DomainCpu(XMLBuilder):
         if guest.os.is_arm_machvirt() and guest.type == "kvm":
             self.mode = self.SPECIAL_MODE_HOST_PASSTHROUGH
 
-        elif guest.os.is_arm64() and guest.os.is_arm_machvirt():
-            # -M virt defaults to a 32bit CPU, even if using aarch64
-            self.set_model(guest, "cortex-a57")
-
         elif guest.os.is_x86() and guest.type == "kvm":
             self._set_cpu_x86_kvm_default(guest)
+
+        else:
+            domcaps = guest.lookup_domcaps()
+
+            # Prefer to emulate a feature-rich CPU instead of a basic one
+            if (self._should_use_maximum_cpu_mode(guest, domcaps)):
+                self.set_special_mode(guest, self.SPECIAL_MODE_MAXIMUM)

virtinst/domcapabilities.py

@@ -382,6 +382,10 @@ class DomainCapabilities(XMLBuilder):
         return (m and m.supported and
                 "on" in m.get_enum("hostPassthroughMigratable").get_values())
 
+    def supports_maximum_cpu_mode(self):
+        m = self.cpu.get_mode("maximum")
+        return (m and m.supported)
+
     def get_cpu_models(self):
         models = []