Re: [Qemu-devel] [PATCH 4/4] s390x/pci: add iommu replay callback

[Yi Min Zhao <zyimin@linux.vnet.ibm.com>]

在 2017/8/28 下午11:57, Cornelia Huck 写道:
> On Mon, 28 Aug 2017 10:04:47 +0200
> Yi Min Zhao <zyimin@linux.vnet.ibm.com> wrote:
>
>> Let's introduce iommu replay callback for s390 pci iommu memory region.
>> Currently we don't need any dma mapping replay. So let it return
>> directly. This implementation will avoid meaningless loops calling
>> translation callback.
>>
>> Reviewed-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>> Signed-off-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
>> ---
>>   hw/s390x/s390-pci-bus.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
>> index 9e1f7ff5c5..359509ccea 100644
>> --- a/hw/s390x/s390-pci-bus.c
>> +++ b/hw/s390x/s390-pci-bus.c
>> @@ -407,6 +407,13 @@ static IOMMUTLBEntry s390_translate_iommu(IOMMUMemoryRegion *mr, hwaddr addr,
>>       return ret;
>>   }
>>   
>> +static void s390_pci_iommu_replay(IOMMUMemoryRegion *iommu,
>> +                                  IOMMUNotifier *notifier)
>> +{
>> +    /* we don't need iommu replay currently */
> This really needs to be heavier on the _why_. My guess is that anything
> which would require replay goes through the rpcit instruction?
My understanding is:
Our arch is different from others. Each pci device has its own iommu, not
like other archs' implementation. So currently there must be no existing
mappings belonging to any newly plugged pci device whose iommu doesn't
have any mapping at the time.
In addition, it's also due to vfio blocking migration. If vfio-pci supports
migration in future, we could implement iommu replay by that time.
>
>> +    return;
>> +}
>> +
>>   static S390PCIIOMMU *s390_pci_get_iommu(S390pciState *s, PCIBus *bus,
>>                                           int devfn)
>>   {
>> @@ -1055,6 +1062,7 @@ static void s390_iommu_memory_region_class_init(ObjectClass *klass, void *data)
>>       IOMMUMemoryRegionClass *imrc = IOMMU_MEMORY_REGION_CLASS(klass);
>>   
>>       imrc->translate = s390_translate_iommu;
>> +    imrc->replay = s390_pci_iommu_replay;
>>   }
>>   
>>   static const TypeInfo s390_iommu_memory_region_info = {
>
>