Re: [libvirt] [PATCH] S390: Enhance memballoon handling for virtio-s390

The way in that memory balloon suppression was handled for S390 is flawed for a number or reasons. 1. Just preventing the default balloon to be created in the case of VIR_ARCH_S390[X] is not sufficient. An explicit memballoon element in the guest definition will still be honored, resulting both in a -balloon option and the allocation of a PCI bus address, neither being supported. 2. Prohibiting balloon for S390 altogether at a domain_conf level is no good solution either as there's work in progress on the QEMU side to implement a virtio-balloon device, although in conjunction with a new machine type. Suppressing the balloon should therefore be done at the QEMU driver level depending on the present capabilities. Therefore we remove the conditional suppression of the default balloon in domain_conf.c. Further, we are claiming the memballoon device for virtio-s390 during device address assignment to prevent it from being considered as a PCI device. Finally, we suppress the generation of the balloon command line option if this is a virtio-s390 machine. Signed-off-by: Viktor Mihajlovski <mihajlov(a)linux.vnet.ibm.com&gt; --- src/conf/domain_conf.c | 4 +--- src/qemu/qemu_command.c | 9 ++++++++- 2 files changed, 9 insertions(+), 4 deletions(-)

@@ -6956,6 +6960,9 @@ qemuBuildCommandLine(virConnectPtr conn, * NB: Earlier we declared that VirtIO balloon will always be in * slot 0x3 on bus 0x0 */ + if (qemuCapsGet(caps, QEMU_CAPS_VIRTIO_S390) && (def->memballoon))

+ def->memballoon->model = VIR_DOMAIN_MEMBALLOON_MODEL_NONE; + if ((def->memballoon) &&

(def->memballoon->model != VIR_DOMAIN_MEMBALLOON_MODEL_NONE)) { if (def->memballoon->model != VIR_DOMAIN_MEMBALLOON_MODEL_VIRTIO) {