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@redhat.com>
---
 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 e93333669..632f330f7 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
+ * @granularity: return location for vCPU hotplug granularity
+ *
+ * With QEMU 2.7 and newer, vCPUs can only be hotplugged @granularity at
+ * a time; because of that, QEMU will not allow guests to start unless the
+ * initial number of vCPUs is a multiple of @granularity.
+ *
+ * Returns 0 on success, 1 if topology is not configured and -1 on error.
+ */
+static int
+qemuDomainDefGetVcpuHotplugGranularity(const virDomainDef *def,
+                                       unsigned int *granularity)
+{
+    if (!granularity)
+        return -1;
+
+    if (!def->cpu || def->cpu->sockets == 0)
+        return 1;
+
+    if (qemuDomainIsPSeries(def))
+        *granularity = def->cpu->threads;
+    else
+        *granularity = 1;
+
+    return 0;
+}
+
+
 #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;
 
         /* Max vCPU count and overall vCPU topology must agree */
         if (virDomainDefGetVcpusTopology(def, &topologycpus) == 0 &&
@@ -3371,6 +3402,16 @@ qemuDomainDefValidate(const virDomainDef *def,
                            _("CPU topology doesn't match maximum vcpu count"));
             goto cleanup;
         }
+
+        /* vCPU hotplug granularity must be respected */
+        if (qemuDomainDefGetVcpuHotplugGranularity(def, &granularity) == 0 &&
+            (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

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On Thu, Dec 14, 2017 at 17:29:51 +0100, Andrea Bolognani wrote:
> 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@redhat.com>
> ---
>  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 e93333669..632f330f7 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
> + * @granularity: return location for vCPU hotplug granularity
> + *
> + * With QEMU 2.7 and newer, vCPUs can only be hotplugged @granularity at
> + * a time; because of that, QEMU will not allow guests to start unless the
> + * initial number of vCPUs is a multiple of @granularity.
> + *
> + * Returns 0 on success, 1 if topology is not configured and -1 on error.
> + */
> +static int
> +qemuDomainDefGetVcpuHotplugGranularity(const virDomainDef *def,
> +                                       unsigned int *granularity)
> +{
> +    if (!granularity)
> +        return -1;

Why?

> +
> +    if (!def->cpu || def->cpu->sockets == 0)
> +        return 1;

I think we assume '1' as threads here if it's not specified.

> +
> +    if (qemuDomainIsPSeries(def))
> +        *granularity = def->cpu->threads;
> +    else
> +        *granularity = 1;

Why not just return the granularity rather than this weirdness?

> +
> +    return 0;
> +}
> +
> +
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On Fri, 2017-12-15 at 13:22 +0100, Peter Krempa wrote:
> > +
> > +    if (!def->cpu || def->cpu->sockets == 0)
> > +        return 1;
> 
> I think we assume '1' as threads here if it's not specified.

Okay.

> > +
> > +    if (qemuDomainIsPSeries(def))
> > +        *granularity = def->cpu->threads;
> > +    else
> > +        *granularity = 1;
> 
> Why not just return the granularity rather than this weirdness?

Sure, I can do that.

Does the rest of the patch look reasonable, or do you want to
point out anything else before I respin?

-- 
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