Hi,

when I try to start qemu with a 7455 processor like my host processor, it
doesn't do anything. Qemu starts, but nothing happens. It eates up the
whole CPU.

As a simple test case, try running

# qemu-system-ppc -M mac99 -cpu 7455 -prom-env 'auto-boot?=false'

and wait for a Openfirmware prompt. I don't get one. A 7400 processor
works fine, but I would like to use the same as my native processor to
get the most out of the virtualization.

Bye, Jörg.

This bugreport has been here for quite some time, and it is still valid
for current version of qemu (which is 2.0-tobe).

Yes, qemu does not work for this cpu type (-cpu 7455), but it works just
fine for some other, similar, cpu types.

Here's what the ppc qemu maintainer says about this issue:

 <agraf> iirc the problem with 7455 is that it has a soft-tlb mmu model by default
 <agraf> and we'd probably have to switch it over into htab mode in openbios or so
 <agraf> no os I'm aware of uses the soft-tlb mode anyways
 <agraf> but why bother? just use -cpu G4 and be happy :)

Or better yet, just use kvm mode, which automatically enables -cpu host.

Please note that using the same cpu type as on your host, but at the same
time running in TCG (emulation, non-kvm) mode, does NOT make the guest
faster.  The cpu is emulated anyway, and in this mode, it is easier and
faster to emulate simpler cpu with simpler instructions..  So choosing
host cpu in TCG mode makes no real sense.

I'm lowering the severity of this bug, because it is trivial to work
around it.

Thanks,

/mjt

Version: 1:7.2+dfsg-1

This works for a long time now, I've no idea when exactly it started to
work but bookworm version of qemu definitely works, and a few version
before it works too.

Let's close this bug report finally, with bookworm version of qemu.

Thanks,

/mjt