Allow runner scripts to fall-back to emulated CPU.

- Refactor the QemuTarget selection of CPU to emulate, to allow it to
  run x64 under software emulated CPU.
- Enable software-emulated-CPU fall-back by default, if /dev/kvm is not
  accessible for reading & writing.
- Add a require_kvm parameter to QemuTarget, and wire it to a common
  --qemu-require-kvm command-line argument.
- Add --qemu-require-kvm to the Fuchsia x64 builders, to ensure that we
  spot any regressions that break KVM on the bots.

Bug: 902607
Change-Id: I60f69b7cb7f5458ccf4a0a2d932235d823b6f932
Reviewed-on: https://chromium-review.googlesource.com/c/1318832Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606157}

build/fuchsia/common_args.py

@@ -60,6 +60,10 @@ def AddCommonArgs(arg_parser):
   common_args.add_argument('--qemu-cpu-cores', type=int, default=4,
                            help='Sets the number of CPU cores to provide if '
                            'launching in a VM with QEMU.'),
+  common_args.add_argument('--qemu-require-kvm', action='store_true',
+                           help='Disables fall-back to emulated CPU if the '
+                           'host system does not support KVM acceleration.'),
+
 
 def ConfigureLogging(args):
   """Configures the logging level based on command line |args|."""
@@ -91,7 +95,8 @@ def GetDeploymentTargetForArgs(args):
 
   if not args.device:
     return QemuTarget(args.output_directory, args.target_cpu,
-                      args.qemu_cpu_cores, system_log_file)
+                      args.qemu_cpu_cores, system_log_file,
+                      args.qemu_require_kvm)
   else:
     return DeviceTarget(args.output_directory, args.target_cpu, args.host,
                         args.port, args.ssh_config, system_log_file)

build/fuchsia/qemu_target.py

@@ -35,7 +35,7 @@ def _GetAvailableTcpPort():
 
 class QemuTarget(target.Target):
   def __init__(self, output_dir, target_cpu, cpu_cores, system_log_file,
-               ram_size_mb=2048):
+               require_kvm, ram_size_mb=2048):
     """output_dir: The directory which will contain the files that are
                    generated to support the QEMU deployment.
     target_cpu: The emulated target CPU architecture.
@@ -45,6 +45,7 @@ class QemuTarget(target.Target):
     self._ram_size_mb = ram_size_mb
     self._system_log_file = system_log_file
     self._cpu_cores = cpu_cores
+    self._require_kvm = require_kvm
 
   def __enter__(self):
     return self
@@ -101,11 +102,10 @@ class QemuTarget(target.Target):
         '-append', ' '.join(kernel_args)
       ]
 
-    # Configure the machine & CPU to emulate, based on the target architecture.
+    # Configure the machine to emulate, based on the target architecture.
     if self._target_cpu == 'arm64':
       qemu_command.extend([
           '-machine','virt',
-          '-cpu', 'cortex-a53',
       ])
       netdev_type = 'virtio-net-pci'
     else:
@@ -114,15 +114,21 @@ class QemuTarget(target.Target):
       ])
       netdev_type = 'e1000'
 
-    # On Linux, enable lightweight virtualization (KVM) if the host and guest
-    # architectures are the same.
-    if sys.platform.startswith('linux'):
-      if self._target_cpu == 'arm64' and platform.machine() == 'aarch64':
-        qemu_command.append('-enable-kvm')
-      elif self._target_cpu == 'x64' and platform.machine() == 'x86_64':
-        qemu_command.extend([
-            '-enable-kvm', '-cpu', 'host,migratable=no',
-        ])
+    # Configure the CPU to emulate.
+    # On Linux, we can enable lightweight virtualization (KVM) if the host and
+    # guest architectures are the same.
+    enable_kvm = self._require_kvm or (sys.platform.startswith('linux') and (
+        (self._target_cpu == 'arm64' and platform.machine() == 'aarch64') or
+        (self._target_cpu == 'x64' and platform.machine() == 'x86_64')) and
+      os.access('/dev/kvm', os.R_OK | os.W_OK))
+    if enable_kvm:
+      qemu_command.extend(['-enable-kvm', '-cpu', 'host,migratable=no'])
+    else:
+      logging.warning('Unable to launch QEMU with KVM acceleration.')
+      if self._target_cpu == 'arm64':
+        qemu_command.extend(['-cpu', 'cortex-a53'])
+      else:
+        qemu_command.extend(['-cpu', 'Haswell,+smap,-check,-fsgsbase'])
 
     # Configure virtual network. It is used in the tests to connect to
     # testserver running on the host.

testing/buildbot/chromium.linux.json

@@ -650,6 +650,9 @@
     ],
     "gtest_tests": [
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -662,7 +665,8 @@
       },
       {
         "args": [
-          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.content_unittests.filter"
+          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.content_unittests.filter",
+          "--qemu-require-kvm"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
@@ -675,6 +679,9 @@
         "test": "content_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -686,6 +693,9 @@
         "test": "cronet_tests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -697,6 +707,9 @@
         "test": "cronet_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -708,6 +721,9 @@
         "test": "crypto_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -720,7 +736,8 @@
       },
       {
         "args": [
-          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.ipc_tests.filter"
+          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.ipc_tests.filter",
+          "--qemu-require-kvm"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
@@ -733,6 +750,9 @@
         "test": "ipc_tests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -745,7 +765,8 @@
       },
       {
         "args": [
-          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.mojo_unittests.filter"
+          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.mojo_unittests.filter",
+          "--qemu-require-kvm"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
@@ -758,6 +779,9 @@
         "test": "mojo_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -769,6 +793,9 @@
         "test": "service_manager_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -780,6 +807,9 @@
         "test": "skia_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -792,7 +822,8 @@
       },
       {
         "args": [
-          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.ui_base_unittests.filter"
+          "--test-launcher-filter-file=../../testing/buildbot/filters/fuchsia.ui_base_unittests.filter",
+          "--qemu-require-kvm"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
@@ -805,6 +836,9 @@
         "test": "ui_base_unittests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
@@ -816,6 +850,9 @@
         "test": "webrunner_browsertests"
       },
       {
+        "args": [
+          "--qemu-require-kvm"
+        ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "dimension_sets": [

testing/buildbot/waterfalls.pyl

@@ -2593,6 +2593,9 @@
         'additional_compile_targets': [
           'all',
         ],
+        'args': [
+          '--qemu-require-kvm',
+        ],
         'swarming': {
           'dimension_sets': [
             {
@@ -2609,6 +2612,9 @@
           'cast_shell',
           'cast_test_lists',
         ],
+        'args': [
+          '--qemu-require-kvm',
+        ],
       },
       'Leak Detection Linux': {
         'test_suites': {

third_party/blink/tools/blinkpy/web_tests/port/fuchsia.py

@@ -119,7 +119,7 @@ class _TargetHost(object):
         try:
             self._target = None
             self._target = qemu_target.QemuTarget(
-                build_path, 'x64', ram_size_mb=8192)
+                build_path, 'x64', require_kvm=True, ram_size_mb=8192)
             self._target.Start()
             self._setup_target(build_path, ports_to_forward)
         except: