RE: [PATCH v3 2/3] vfio/pci: Fix a segfault in vfio_realize

[Duan, Zhenzhong]

>-----Original Message-----
>From: Joao Martins <joao.m.martins@oracle.com>
>Sent: Wednesday, June 21, 2023 7:09 PM
>To: Duan, Zhenzhong <zhenzhong.duan@intel.com>
>Cc: alex.williamson@redhat.com; clg@redhat.com; qemu-devel@nongnu.org;
>avihaih@nvidia.com; Peng, Chao P <chao.p.peng@intel.com>
>Subject: Re: [PATCH v3 2/3] vfio/pci: Fix a segfault in vfio_realize
>
>
>
>On 21/06/2023 09:02, Zhenzhong Duan wrote:
>> In case irqchip_change_notifier isn't added, removing it triggers segfault.
>>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>> ---
>>  hw/vfio/pci.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index
>> c71b0955d81c..82c4cf4f7609 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -3222,7 +3222,9 @@ static void vfio_realize(PCIDevice *pdev, Error
>> **errp)
>>
>>  out_deregister:
>>      pci_device_set_intx_routing_notifier(&vdev->pdev, NULL);
>> -    kvm_irqchip_remove_change_notifier(&vdev->irqchip_change_notifier);
>> +    if (vdev->irqchip_change_notifier.notify) {
>> +        kvm_irqchip_remove_change_notifier(&vdev-
>>irqchip_change_notifier);
>> +    }
>
>If the first patch ends up being pursued (which I am not quite sure) it should
>be folded in the previous patch, as the out_deregister is used starting your
>patch 1.
Sorry for late response, just back from vacation.

out_deregister isn't only for vfio migration, there are some other jump sites 
to out_deregister in vfio_realize. Take below code for example:

    if (vdev->display_xres || vdev->display_yres) {
        if (vdev->dpy == NULL) {
            error_setg(errp, "xres and yres properties require display=on");
            goto out_deregister;
        }

I can reproduce a segmentation fault when hotplug a vfio device using below cmd:
(qemu) device_add vfio-pci,host=81:11.1,id=vfio1,bus=root1,xres=1 Connection 
closed by foreign host.

After fix:
(qemu) device_add vfio-pci,host=81:11.1,id=vfio1,bus=root1,xres=1
Error: vfio 0000:81:11.1: xres and yres properties require display=on
(qemu)

Thanks
Zhenzhong