Re: [Qemu-devel] [PATCH 2/2] pci: introduce a bus master container

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/03/2017 10:38, Marcel Apfelbaum wrote:
> On 03/13/2017 05:29 AM, Jason Wang wrote:
>> 96a8821d2141 ("virtio: unbreak virtio-pci with IOMMU after caching ring
>> translations") tries to make IOMMU works with virtio memory region
>> cache, but it requires IOMMU to be created before any virtio
>> devices. This is sub optimal, fixing this by introduce a bus master
>> container to make sure address space can be initialized during device
>> registering, and then we can safely set alias and make
>> bus_master_enable_region as its subregion during bus master
>> initialization.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>  hw/pci/pci.c         | 9 +++++++--
>>  include/hw/pci/pci.h | 1 +
>>  2 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> index 273f1e4..ad46390 100644
>> --- a/hw/pci/pci.c
>> +++ b/hw/pci/pci.c
>> @@ -88,8 +88,8 @@ static void pci_init_bus_master(PCIDevice *pci_dev)
>>                               OBJECT(pci_dev), "bus master",
>>                               dma_as->root, 0,
>> memory_region_size(dma_as->root));
>>      memory_region_set_enabled(&pci_dev->bus_master_enable_region,
>> false);
>> -    address_space_init(&pci_dev->bus_master_as,
>> -                       &pci_dev->bus_master_enable_region,
>> pci_dev->name);
>> +   
>> memory_region_add_subregion(&pci_dev->bus_master_container_region, 0,
>> +                                &pci_dev->bus_master_enable_region);
> 
> Hi Jason,
> 
> The patch looks good to me, I only have one question:
> On hot-unplug, shouldn't we remove the "new" sub-region ?

It should be done automatically:

    /* We know the region is not visible in any address space (it
     * does not have a container and cannot be a root either because
     * it has no references, so we can blindly clear mr->enabled.
     * memory_region_set_enabled instead could trigger a transaction
     * and cause an infinite loop.
     */
    mr->enabled = false;
    memory_region_transaction_begin();
    while (!QTAILQ_EMPTY(&mr->subregions)) {
        MemoryRegion *subregion = QTAILQ_FIRST(&mr->subregions);
        memory_region_del_subregion(mr, subregion);
    }
    memory_region_transaction_commit();

It's relatively new though (QEMU v2.5+).

Paolo

> Thanks,
> Marcel
> 
>>  }
>>
>>  static void pcibus_machine_done(Notifier *notifier, void *data)
>> @@ -995,6 +995,11 @@ static PCIDevice
>> *do_pci_register_device(PCIDevice *pci_dev, PCIBus *bus,
>>      pci_dev->devfn = devfn;
>>      pci_dev->requester_id_cache = pci_req_id_cache_get(pci_dev);
>>
>> +    memory_region_init(&pci_dev->bus_master_container_region,
>> OBJECT(pci_dev),
>> +                       "bus master container", UINT64_MAX);
>> +    address_space_init(&pci_dev->bus_master_as,
>> +                       &pci_dev->bus_master_container_region,
>> pci_dev->name);
>> +
>>      if (qdev_hotplug) {
>>          pci_init_bus_master(pci_dev);
>>      }
>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>> index 9349acb..713ede0 100644
>> --- a/include/hw/pci/pci.h
>> +++ b/include/hw/pci/pci.h
>> @@ -284,6 +284,7 @@ struct PCIDevice {
>>      char name[64];
>>      PCIIORegion io_regions[PCI_NUM_REGIONS];
>>      AddressSpace bus_master_as;
>> +    MemoryRegion bus_master_container_region;
>>      MemoryRegion bus_master_enable_region;
>>
>>      /* do not access the following fields */
>>
>