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| author | Eduardo Habkost <ehabkost@redhat.com> | 2019-12-05 19:33:39 -0300 |
|---|---|---|
| committer | Eduardo Habkost <ehabkost@redhat.com> | 2019-12-19 14:38:51 -0300 |
| commit | ad18392892c04637fb56956d997f4bc600224356 (patch) | |
| tree | 0851524dcf34914d303a9baa8a08383121ee971e | |
| parent | aceeaa69d28e6f08a24395d0aa6915b687d0a681 (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>
| -rw-r--r-- | qemu-deprecated.texi | 8 | ||||
| -rw-r--r-- | target/i386/cpu.c | 8 |
2 files changed, 15 insertions, 1 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 diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 0a9ac65974..ba5e9d5d6b 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -3981,7 +3981,13 @@ static PropValue tcg_default_props[] = { }; -X86CPUVersion default_cpu_version = CPU_VERSION_LATEST; +/* + * We resolve CPU model aliases using -v1 when using "-machine + * none", but this is just for compatibility while libvirt isn't + * adapted to resolve CPU model versions before creating VMs. + * See "Runnability guarantee of CPU models" at * qemu-deprecated.texi. + */ +X86CPUVersion default_cpu_version = 1; void x86_cpu_set_default_version(X86CPUVersion version) { |