[Qemu-ppc] KVM memory slots limit on powerpc

[Thomas Huth]

 Hi all,

now that we get memory hotplugging for the spapr machine on qemu-ppc,
too, it seems like we easily can hit the amount of KVM-internal memory
slots now ("#define KVM_USER_MEM_SLOTS 32" in
arch/powerpc/include/asm/kvm_host.h). For example, start
qemu-system-ppc64 with a couple of "-device secondary-vga" and "-m
4G,slots=32,maxmem=40G" and then try to hot-plug all 32 DIMMs ... and
you'll see that it aborts way earlier already.

The x86 code already increased the amount of KVM_USER_MEM_SLOTS to 509
already (+3 internal slots = 512) ... maybe we should now increase the
amount of slots on powerpc, too? Since we don't use internal slots on
POWER, would 512 be a good value? Or would less be sufficient, too?

 Thomas