While at the moment we're only performing a single check that is connected to vCPU hotplugging, we're going to introduce a second one soon. Move the topology check underneath the capability check to make that easier; since, after this change, the 'topologycpus' variable doesn't need to have function scope, we move its declaration to the inner scope as well. The comments around the check are modified in order to explain the different QEMU versions involved. Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- src/qemu/qemu_domain.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index 74b82450b..227ba32a7 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -3299,7 +3299,6 @@ qemuDomainDefValidate(const virDomainDef *def, { virQEMUDriverPtr driver = opaque; virQEMUCapsPtr qemuCaps = NULL; - unsigned int topologycpus; int ret = -1; if (!(qemuCaps = virQEMUCapsCacheLookup(driver->qemuCapsCache, @@ -3359,11 +3358,17 @@ qemuDomainDefValidate(const virDomainDef *def, } } - /* qemu as of 2.5.0 rejects SMP topologies that don't match the cpu count */ - if (virDomainDefGetVcpusTopology(def, &topologycpus) == 0 && - topologycpus != virDomainDefGetVcpusMax(def)) { - /* presence of query-hotpluggable-cpus should be a good enough witness */ - if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS)) { + /* QEMU 2.7 (detected via the availability of query-hotpluggable-cpus) + * enforces stricter rules than previous versions when it comes to guest + * CPU topology. Verify known constraints are respected */ + if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS)) { + unsigned int topologycpus; + + /* Starting from QEMU 2.5, max vCPU count and overall vCPU topology + * must agree. We only actually enforce this with QEMU 2.7+, due + * to the capability check above */ + if (virDomainDefGetVcpusTopology(def, &topologycpus) == 0 && + topologycpus != virDomainDefGetVcpusMax(def)) { virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", _("CPU topology doesn't match maximum vcpu count")); goto cleanup; -- 2.14.3

QEMU 2.7 and newer don't allow guests to start unless the initial vCPUs count is a multiple of the vCPU hotplug granularity, so validate it and report an error if needed. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1283700 Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- src/qemu/qemu_domain.c | 41 ++++++++++++++++++++++ tests/qemuxml2argvdata/cpu-hotplug-granularity.xml | 18 ++++++++++ tests/qemuxml2argvtest.c | 3 ++ 3 files changed, 62 insertions(+) create mode 100644 tests/qemuxml2argvdata/cpu-hotplug-granularity.xml diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index 227ba32a7..43bd0fff4 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -3289,6 +3289,36 @@ qemuDomainDefValidateVideo(const virDomainDef *def) } +/** + * qemuDomainDefGetVcpuHotplugGranularity: + * @def: domain definition + * + * With QEMU 2.7 and newer, vCPUs can only be hotplugged in groups that + * respect the guest's hotplug granularity; because of that, QEMU will + * not allow guests to start unless the initial number of vCPUs is a + * multiple of the hotplug granularity. + * + * Returns the vCPU hotplug granularity. + */ +static unsigned int +qemuDomainDefGetVcpuHotplugGranularity(const virDomainDef *def) +{ + /* If the guest CPU topology has not been configured, assume we + * can hotplug vCPUs one at a time */ + if (!def->cpu || def->cpu->sockets == 0) + return 1; + + /* For pSeries guests, hotplug can only be performed one core + * at a time, so the vCPU hotplug granularity is the number + * of threads per core */ + if (qemuDomainIsPSeries(def)) + return def->cpu->threads; + + /* In all other cases, we can hotplug vCPUs one at a time */ + return 1; +} + + #define QEMU_MAX_VCPUS_WITHOUT_EIM 255 @@ -3363,6 +3393,7 @@ qemuDomainDefValidate(const virDomainDef *def, * CPU topology. Verify known constraints are respected */ if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS)) { unsigned int topologycpus; + unsigned int granularity; /* Starting from QEMU 2.5, max vCPU count and overall vCPU topology * must agree. We only actually enforce this with QEMU 2.7+, due @@ -3373,6 +3404,16 @@ qemuDomainDefValidate(const virDomainDef *def, _("CPU topology doesn't match maximum vcpu count")); goto cleanup; } + + /* vCPU hotplug granularity must be respected */ + granularity = qemuDomainDefGetVcpuHotplugGranularity(def); + if ((virDomainDefGetVcpus(def) % granularity) != 0) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, + _("vCPUs count must be a multiple of the vCPU " + "hotplug granularity (%u)"), + granularity); + goto cleanup; + } } if (ARCH_IS_X86(def->os.arch) && diff --git a/tests/qemuxml2argvdata/cpu-hotplug-granularity.xml b/tests/qemuxml2argvdata/cpu-hotplug-granularity.xml new file mode 100644 index 000000000..a94f41e46 --- /dev/null +++ b/tests/qemuxml2argvdata/cpu-hotplug-granularity.xml @@ -0,0 +1,18 @@ +<domain type='qemu'> + <name>guest</name> + <uuid>1ccfd97d-5eb4-478a-bbe6-88d254c16db7</uuid> + <memory unit='KiB'>524288</memory> + <vcpu placement='static' current='2'>8</vcpu> + <os> + <type arch='ppc64' machine='pseries'>hvm</type> + </os> + <cpu> + <topology sockets='1' cores='2' threads='4'/> + </cpu> + <devices> + <emulator>/usr/bin/qemu-system-ppc64</emulator> + <controller type='pci' model='pci-root'/> + <controller type='usb' model='none'/> + <memballoon model='none'/> + </devices> +</domain> diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c index ca24e0bbb..10ab8d787 100644 --- a/tests/qemuxml2argvtest.c +++ b/tests/qemuxml2argvtest.c @@ -2900,6 +2900,9 @@ mymain(void) QEMU_CAPS_DEVICE_INTEL_IOMMU); DO_TEST("cpu-hotplug-startup", QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS); + DO_TEST_PARSE_ERROR("cpu-hotplug-granularity", + QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS); + DO_TEST("virtio-options", QEMU_CAPS_VIRTIO_SCSI, QEMU_CAPS_VIRTIO_KEYBOARD, QEMU_CAPS_VIRTIO_MOUSE, QEMU_CAPS_VIRTIO_TABLET, QEMU_CAPS_VIRTIO_INPUT_HOST, -- 2.14.3