On Mon, Jan 15, 2018 at 03:25:18PM +0100, Jiri Denemark wrote:
On Mon, Jan 15, 2018 at 12:04:55 -0200, Eduardo Habkost wrote:
CCing libvirt developers. ... This case is slightly more problematic, however: the new feature is actually migratable (under very controlled circumstances) because of patch 2/2, but it is not migration-safe[1]. This means libvirt shouldn't include it in "host-model" expansion (which uses the query-cpu-model-expansion QMP command) until we make the feature migration-safe.
For QEMU, this means the feature shouldn't be returned by "query-cpu-model-expansion type=static model=max" (but it can be returned by "query-cpu-model-expansion type=full model=max").
Jiri, it looks like libvirt uses type=full on query-cpu-model-expansion on x86. It needs to use type=static[2], or it will have no way to find out if a feature is migration-safe or not. ... [2] It looks like libvirt uses type=full because it wants to get all QOM property aliases returned. In this case, one solution for libvirt is to use:
static_expansion = query_cpu_model_expansion(type=static, model) all_props = query_cpu_model_expansion(type=full, static_expansion)
This is exactly what libvirt is doing (with model = "host") ever since query-cpu-model-expansion support was implemented for x86.
Oh, now I see that the x86 code uses QEMU_MONITOR_CPU_MODEL_EXPANSION_STATIC_FULL and not just QEMU_MONITOR_CPU_MODEL_EXPANSION_FULL. Nice! -- Eduardo