Re: [PATCH v4] failover: unregister ROM on unplug

[Laurent Vivier]

On 03/08/2021 16:04, Michael S. Tsirkin wrote:
> On Wed, Jul 21, 2021 at 06:09:05PM +0200, Laurent Vivier wrote:
>> The intend of failover is to allow to migrate a VM with a VFIO
>> networking card without disrupting the network operation by switching
>> to a virtio-net device during the migration.
>>
>> This simple change allows to test failover with a simulated device
>> like e1000e rather than a vfio device, even if it's useless in real
>> life it can help to debug failover.
>>
>> This is interesting to developers that want to test failover on
>> a system with no vfio device. Moreover it simplifies host networking
>> configuration as we can use the same bridge for virtio-net and
>> the other failover networking device.
>>
>> Without this change the migration of a system configured with failover
>> fails with:
>>
>>   ...
>>   -device virtio-net-pci,id=virtionet0,failover=on,...  \
>>   -device e1000,failover_pair_id=virtionet0,... \
>>   ...
>>
>>   (qemu) migrate ...
>>
>>   Unknown ramblock "0000:00:01.1:00.0/e1000e.rom", cannot accept migration
>>   error while loading state for instance 0x0 of device 'ram'
>>   load of migration failed: Invalid argument
>>
>> This happens because QEMU correctly unregisters the interface vmstate but
>> not the ROM one. This patch fixes that.
>>
>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> 
> 
> Build fails on qemu-system-m68k:
> 
> /usr/bin/ld: libqemu-m68k-softmmu.fa.p/hw_net_virtio-net.c.o: in function 
> `virtio_net_handle_migration_primary':
> /scm/qemu/build/../hw/net/virtio-net.c:3259: undefined reference to 
> `pci_del_option_rom'
> collect2: error: ld returned 1 exit status
> ninja: build stopped: subcommand failed.
> make[1]: *** [Makefile:154: run-ninja] Error 1
> 
> It's not pretty to poke at pci from generic virtio.

I agree with you. The problem is failover is implemented in virtio-net while it 
relies on
virtio-pci hotplug capability.

> Should we maybe wrap vmstate_unregister and pci_del_option_rom
> to allow removing all migrateable things related to the device
> in one go somehow?

I'm going to have a look to see how to do.

I have already a patch that moves all the failover PCI unplug/hotplug functions 
into the
PCI device implementation (and removes all this stuff from virtio-net). Perhaps 
we can
rely on that. The bonus with this moves is it allows to automatically 
unplug/hotplug any
PCI device during a migration without the failover environment (but failover 
uses it).

Thanks,
Laurent

> 
>> ---
>>
>> Notes:
>>     v4:
>>       export and use pci_del_option_rom()
>>     
>>     v3:
>>       remove useless space before comma
>>     
>>     v2:
>>       reset has_rom to false
>>       update commit log message
>>
>>  include/hw/pci/pci.h | 2 ++
>>  hw/net/virtio-net.c  | 1 +
>>  hw/pci/pci.c         | 3 +--
>>  3 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>> index d0f4266e3725..84707034cbf8 100644
>> --- a/include/hw/pci/pci.h
>> +++ b/include/hw/pci/pci.h
>> @@ -369,6 +369,8 @@ void pci_register_vga(PCIDevice *pci_dev, MemoryRegion 
>> *mem,
>>  void pci_unregister_vga(PCIDevice *pci_dev);
>>  pcibus_t pci_get_bar_addr(PCIDevice *pci_dev, int region_num);
>>  
>> +void pci_del_option_rom(PCIDevice *pdev);
>> +
>>  int pci_add_capability(PCIDevice *pdev, uint8_t cap_id,
>>                         uint8_t offset, uint8_t size,
>>                         Error **errp);
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 16d20cdee52a..d6f03633f1b3 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -3256,6 +3256,7 @@ static void 
>> virtio_net_handle_migration_primary(VirtIONet *n, MigrationState *s)
>>      if (migration_in_setup(s) && !should_be_hidden) {
>>          if (failover_unplug_primary(n, dev)) {
>>              vmstate_unregister(VMSTATE_IF(dev), qdev_get_vmsd(dev), dev);
>> +            pci_del_option_rom(PCI_DEVICE(dev));
>>              qapi_event_send_unplug_primary(dev->id);
>>              qatomic_set(&n->failover_primary_hidden, true);
>>          } else {
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index 23d2ae2ab232..c210d92b5ba7 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -228,7 +228,6 @@ static PCIBus *pci_find_bus_nr(PCIBus *bus, int bus_num);
>>  static void pci_update_mappings(PCIDevice *d);
>>  static void pci_irq_handler(void *opaque, int irq_num, int level);
>>  static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom, Error 
>> **);
>> -static void pci_del_option_rom(PCIDevice *pdev);
>>  
>>  static uint16_t pci_default_sub_vendor_id = 
>> PCI_SUBVENDOR_ID_REDHAT_QUMRANET;
>>  static uint16_t pci_default_sub_device_id = PCI_SUBDEVICE_ID_QEMU;
>> @@ -2429,7 +2428,7 @@ static void pci_add_option_rom(PCIDevice *pdev, bool 
>> is_default_rom,
>>      pci_register_bar(pdev, PCI_ROM_SLOT, 0, &pdev->rom);
>>  }
>>  
>> -static void pci_del_option_rom(PCIDevice *pdev)
>> +void pci_del_option_rom(PCIDevice *pdev)
>>  {
>>      if (!pdev->has_rom)
>>          return;
>> -- 
>> 2.31.1
>