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authorEduardo Habkost <ehabkost@redhat.com>2019-12-05 19:33:39 -0300
committerEduardo Habkost <ehabkost@redhat.com>2019-12-19 14:38:51 -0300
commitad18392892c04637fb56956d997f4bc600224356 (patch)
tree0851524dcf34914d303a9baa8a08383121ee971e /qemu-deprecated.texi
parentaceeaa69d28e6f08a24395d0aa6915b687d0a681 (diff)
i386: Resolve CPU models to v1 by default
When using `query-cpu-definitions` using `-machine none`, QEMU is resolving all CPU models to their latest versions. The actual CPU model version being used by another machine type (e.g. `pc-q35-4.0`) might be different. In theory, this was OK because the correct CPU model version is returned when using the correct `-machine` argument. Except that in practice, this breaks libvirt expectations: libvirt always use `-machine none` when checking if a CPU model is runnable, because runnability is not expected to be affected when the machine type is changed. For example, when running on a Haswell host without TSX, Haswell-v4 is runnable, but Haswell-v1 is not. On those hosts, `query-cpu-definitions` says Haswell is runnable if using `-machine none`, but Haswell is actually not runnable using any of the `pc-*` machine types (because they resolve Haswell to Haswell-v1). In other words, we're breaking the "runnability guarantee" we promised to not break for a few releases (see qemu-deprecated.texi). To address this issue, change the default CPU model version to v1 on all machine types, so we make `query-cpu-definitions` output when using `-machine none` match the results when using `pc-*`. This will change in the future (the plan is to always return the latest CPU model version if using `-machine none`), but only after giving libvirt the opportunity to adapt. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1779078 Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Message-Id: <20191205223339.764534-1-ehabkost@redhat.com> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Diffstat (limited to 'qemu-deprecated.texi')
-rw-r--r--qemu-deprecated.texi8
1 files changed, 8 insertions, 0 deletions
diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
index 62680f7bd5..7b94653cef 100644
--- a/qemu-deprecated.texi
+++ b/qemu-deprecated.texi
@@ -367,6 +367,14 @@ guarantees must resolve the CPU model aliases using te
``alias-of'' field returned by the ``query-cpu-definitions'' QMP
command.
+While those guarantees are kept, the return value of
+``query-cpu-definitions'' will have existing CPU model aliases
+point to a version that doesn't break runnability guarantees
+(specifically, version 1 of those CPU models). In future QEMU
+versions, aliases will point to newer CPU model versions
+depending on the machine type, so management software must
+resolve CPU model aliases before starting a virtual machine.
+
@node Recently removed features
@appendix Recently removed features