[PATCH 2/5] machine.py: add default pseries params in machine.py

[Daniel Henrique Barboza]

pSeries guests set a handful of machine capabilities on by default, all
of them related to security mitigations, that aren't always available in
the host.

This means that, as is today, running avocado in a Power9 server without
the proper firmware support, and with --disable-tcg, this error will
occur:

 (1/1) tests/avocado/info_usernet.py:InfoUsernet.test_hostfwd: ERROR: 
ConnectError:
Failed to establish session: EOFError\n  Exit code: 1\n  (...)
(...)
        Command: ./qemu-system-ppc64 -display none -vga none (...)
        Output: qemu-system-ppc64: warning: netdev vnet has no peer
qemu-system-ppc64: Requested safe cache capability level not supported by KVM
Try appending -machine cap-cfpc=broken

info_usernet.py happens to trigger this error first, but all tests would
fail in this configuration because the host does not support the default
'cap-cfpc' capability.

A similar situation was already fixed a couple of years ago by Greg Kurz
(commit 63d57c8f91d0) but it was focused on TCG warnings for these same
capabilities and running C qtests. This commit ended up preventing the
problem we're facing with avocado when running qtests with KVM support.

This patch does a similar approach by amending machine.py to disable
these security capabilities in case we're running a pseries guest. The
change is made in the _launch() callback to be sure that we're already
commited into launching the guest. It's also worth noticing that we're
relying on self._machine being set accordingly (i.e. via tag:machine),
which is currently the case for all ppc64 related avocado tests.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 python/qemu/machine/machine.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 07ac5a710b..12e5e37bff 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -51,6 +51,11 @@
 
 
 LOG = logging.getLogger(__name__)
+PSERIES_DEFAULT_CAPABILITIES = ("cap-cfpc=broken,"
+                                "cap-sbbc=broken,"
+                                "cap-ibs=broken,"
+                                "cap-ccf-assist=off,"
+                                "cap-fwnmi=off")
 
 
 class QEMUMachineError(Exception):
@@ -447,6 +452,14 @@ def _launch(self) -> None:
         """
         Launch the VM and establish a QMP connection
         """
+
+        # pseries needs extra machine options to disable Spectre/Meltdown
+        # KVM related capabilities that might not be available in the
+        # host.
+        if "qemu-system-ppc64" in self._binary:
+            if self._machine is None or "pseries" in self._machine:
+                self._args.extend(['-machine', PSERIES_DEFAULT_CAPABILITIES])
+
         self._pre_launch()
         LOG.debug('VM launch command: %r', ' '.join(self._qemu_full_args))
 
-- 
2.32.0