Re: [libvirt] [Qemu-devel] [PATCH for-2.9 00/17] target-i386: Implement query-cpu-model-expansion
Am 02.12.2016 um 22:17 schrieb Eduardo Habkost:
This series implements query-cpu-model-expansion on target-i386.
QAPI / interface changes
------------------------
When implementing this, I have noticed that the "host" CPU model
in i386 includes some migration-unsafe features that can't be
translated to any migration-safe representation: "pmu", and
"host-cache-info".
To be able to handle the migration-unsafe features, I have
extended the query-cpu-model-expansion definition to be clear
about what happens to those features when the CPU model is
expanded (in short: static expansion removes them, full expansion
keeps them).
I think this makes sense. The important part is to really keep static
expansion static :)
I also added "static" and "migration-safe" fields to the return
value of query-cpu-model-expansion, so callers can know if the
the expanded representation is static and migration-safe.
Is static really needed? I can understand why migration-safe might be
of interest, but can't see how "static" could help (I mean we have
static expansion for this purpose). Do you have anything special in
mind regarding exposing "static"?
Test code
---------
I have added a Python test script for the feature, that will try
multiple combinations of the expansion operation, and see if the
returned data keeps matches some constratins.
The test script works with the s390x query-cpu-model-expansion
command, except that: 1) I couldn't test it with KVM; 2) qtest.py
error handling when QEMU refuses to run is unreliable (so the
script needs runnability information to be availble in TCG mode,
too, to skip not-runnable CPU models and avoid problems).
Everything except "host" should behave completely the same on s390x
with or without KVM being active. So with !KVM tests we can already
cover most of the interesting parts. Thanks for taking care of s390x.
Future versions of the test script could run a arch-specific
CPUID-dump guest binary, and validate data seen by the guest
directly. While we don't do that, the script validates all QOM
properties on the CPU objects looking for unexpected changes. At
least in the case of x86, the QOM properties will include lots of
the CPUID data seen by the guest, giving us decent coverage.
Something like that would be cool. Unfortunately, e.g. on s390x some
CPUID-like data (e.g. STFL(E) and SCP info) is only available from
kernel space. So we can't simply run a user space script. However,
something like a kernel module would be possible (or even something like
the s390x pc-bios to simply read and dump the data).
--
David