[libvirt] [PATCH] qemu: Starting a domain with custom model and allowed-fallback failed when host lacks some CPU features

Yi Wang wang.yi59 at zte.com.cn
Tue Jun 6 16:23:01 UTC 2017

An attemp to start a domain requesting a custom CPU model, core2duo, for
example, will fail if some feature that the model needs doesn't exist in that
host, even though fallback attibute is set allow:
"error: the CPU is incompatible with host CPU: Host CPU does not provide
required features: monitor"
Of course we can start that domain through forbidding that feature, but
that may not be flexible.

Signed-off-by: Yi Wang <wang.yi59 at zte.com.cn>
 src/qemu/qemu_process.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 32ba8e3..1bb65d3 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -5324,7 +5324,8 @@ qemuProcessUpdateGuestCPU(virDomainDefPtr def,
                       virQEMUCapsGetHostModel(qemuCaps, def->virtType,
-                      def->cpu, true) < 0)
+                      def->cpu,
+                      def->cpu->fallback != VIR_CPU_FALLBACK_ALLOW) < 0)
         return -1;
     if (virCPUUpdate(def->os.arch, def->cpu,

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