qemu: ppc64: Align memory sizes to 256MiB blocks

For some machine types ppc64 machines now require that memory sizes are
aligned to 256MiB increments (due to the dynamically reconfigurable
memory). As now we treat existing configs reasonably in regards to
migration, we can round all the sizes unconditionally. The only drawback
will be that the memory size of a VM can potentially increase by
(256MiB - 1byte) * number_of_NUMA_nodes.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1249006

src/qemu/qemu_domain.c

@@ -3362,8 +3362,13 @@ qemuDomainAgentAvailable(virDomainObjPtr vm,
 
 
 static unsigned long long
-qemuDomainGetMemorySizeAlignment(virDomainDefPtr def ATTRIBUTE_UNUSED)
+qemuDomainGetMemorySizeAlignment(virDomainDefPtr def)
 {
+    /* PPC requires the memory sizes to be rounded to 256MiB increments, so
+     * round them to the size always. */
+    if (ARCH_IS_PPC64(def->os.arch))
+        return 256 * 1024;
+
     /* Align memory size. QEMU requires rounding to next 4KiB block.
      * We'll take the "traditional" path and round it to 1MiB*/
 

tests/qemuxml2argvdata/qemuxml2argv-pseries-cpu-compat.args

 LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test \
 QEMU_AUDIO_DRV=none /usr/bin/qemu-system-ppc64 -S -M pseries \
 -cpu host,compat=power7 \
--m 214 -smp 4 -nographic -nodefconfig -nodefaults \
+-m 256 -smp 4 -nographic -nodefconfig -nodefaults \
 -chardev socket,id=charmonitor,path=/tmp/test-monitor,server,nowait \
 -mon chardev=charmonitor,id=monitor,mode=readline -no-acpi -boot c -usb \
 -chardev pty,id=charserial0 \