Re: [Qemu-devel] [PATCH] virtio-pci: fix memory MR cleanup for modern

[Paolo Bonzini]

On 27/07/2015 15:30, Paolo Bonzini wrote:
> 
> 
> On 27/07/2015 15:24, Michael S. Tsirkin wrote:
>> +static void virtio_pci_modern_region_unmap(VirtIOPCIProxy *proxy,
>> +                                           VirtIOPCIRegion *region)
>> +{
>> +    memory_region_del_subregion(&proxy->modern_bar,
>> +                                &region->mr);
>> +}
>> +
>>  /* This is called by virtio-bus just after the device is plugged. */
>>  static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
>>  {
>> @@ -1520,8 +1527,16 @@ static void virtio_pci_device_plugged(DeviceState *d, 
>> Error **errp)
>>  static void virtio_pci_device_unplugged(DeviceState *d)
>>  {
>>      VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
>> +    bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN);
>>  
>>      virtio_pci_stop_ioeventfd(proxy);
>> +
>> +    if (modern) {
>> +        virtio_pci_modern_region_unmap(proxy, &proxy->common);
>> +        virtio_pci_modern_region_unmap(proxy, &proxy->isr);
>> +        virtio_pci_modern_region_unmap(proxy, &proxy->device);
>> +        virtio_pci_modern_region_unmap(proxy, &proxy->notify);
>> +    }
>>  }
> 
> Actually this is not necessary.  memory_region_del_subregion is only
> needed inasmuch as it prevents further guest access to the region, so
> it's enough that the toplevel region (the modern_bar itself) is
> unmapped.  The PCI core does that automatically.
> 
> That said, it's polite to unmap everything, so if you want this patch:
> 
> Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>

After discussing on IRC the problem (which is that
memory_region_add_subregion add a reference to the VirtioPCIProxy
object, and you want to remove it), this is indeed the correct fix.

Paolo