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From: Thomas Huth <thuth@redhat.com>
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Date: Fri, 18 Sep 2015 20:42:54 +0200
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Subject: Re: [Qemu-devel] [PATCH 5/7] qdev: Protect device-list-properties
 against broken devices
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To: Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>, ehabkost@redhat.com, Peter Crosthwaite <crosthwaite.peter@gmail.com>, qemu-stable@nongnu.org, Alistair Francis <alistair.francis@xilinx.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Alexander Graf <agraf@suse.de>, qemu-ppc@nongnu.org, Antony Pavlov <antonynpavlov@gmail.com>, stefanha@redhat.com, Cornelia Huck <cornelia.huck@de.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>, afaerber@suse.de, Li Guang <lig.fnst@cn.fujitsu.com>, Richard Henderson <rth@twiddle.net>

On 18/09/15 14:00, Markus Armbruster wrote:
> Several devices don't survive object_unref(object_new(T)): they crash
> or hang during cleanup, or they leave dangling pointers behind.
> 
> This breaks at least device-list-properties, because
> qmp_device_list_properties() needs to create a device to find its
> properties.  Broken in commit f4eb32b "qmp: show QOM properties in
> device-list-properties", v2.1.  Example reproducer:
> 
>     $ qemu-system-aarch64 -nodefaults -display none -machine none -S -qmp stdio
>     {"QMP": {"version": {"qemu": {"micro": 50, "minor": 4, "major": 2}, "package": ""}, "capabilities": []}}
>     { "execute": "qmp_capabilities" }
>     {"return": {}}
>     { "execute": "device-list-properties", "arguments": { "typename": "pxa2xx-pcmcia" } }
>     qemu-system-aarch64: /home/armbru/work/qemu/memory.c:1307: memory_region_finalize: Assertion `((&mr->subregions)->tqh_first == ((void *)0))' failed.
>     Aborted (core dumped)
>     [Exit 134 (SIGABRT)]
> 
> Unfortunately, I can't fix the problems in these devices right now.
> Instead, add DeviceClass member cannot_even_create_with_object_new_yet
> to mark them:
> 
> * Crash or hang during cleanup (didn't debug them, so I can't say
>   why): "pxa2xx-pcmcia", "realview_pci", "versatile_pci",
>   "s390-sclp-event-facility", "sclp"
> 
> * Dangling pointers: all CPUs, plus "allwinner-a10", "digic",
>   "fsl,imx25", "fsl,imx31", "xlnx,zynqmp", because they create CPUs
> 
> * Assert kvm_enabled(): "host-x86_64-cpu", host-i386-cpu",
>   "host-powerpc64-cpu", "host-embedded-powerpc-cpu",
>   "host-powerpc-cpu"

I just had a look at the powerpc code - you're likely talking about
the "assert(kvm_enabled());" in the kvmppc_host_cpu_initfn() in
target-ppc/kvm.c ? That should be fine, I think, because
kvm_ppc_register_host_cpu_type() is only done on ppc when KVM has been
enabled.

 Thomas