Re: [Qemu-devel] [PATCH v2 7/7] intel_iommu: support passthrough (PT)

[Lan Tianyu]

On 2017年04月20日 15:04, Peter Xu wrote:
> On Thu, Apr 20, 2017 at 06:36:16AM +0000, Liu, Yi L wrote:
> 
> [...]
> 
>>>> In my understanding, container->space->as->root cannot work here no
>>>> matter passthru-mode is enabled or not. The code here is aiming to
>>>> check if vIOMMU exists. After the vfio series, the vtd_dev_as->root is
>>>> not initialized to be a iommu MemoryRegion. Compared with checking if
>>>> it is system_memory(), I think adding a mechanism to get the iommu
>>> MemoryRegion may be a better choice. Just like the current
>>> pci_device_iommu_address_space().
>>>
>>> Isn't pci_device_iommu_address_space() used to get that IOMMU memory region?
> 
> Again I should say s/memory region/address space/...
> 
>>
>> It actually returns the AddressSpace, and the AddressSpace includes a memory 
>> region.
>> It is as->root. But after adding the vfio series, through the IOMMU memory 
>> region
>> is got, but it has no iommu_ops. Just as the following code shows. That's 
>> why I said
>> even without passthru-mode, Tianyu's that code snippet is not able to get 
>> the correct
>> check.
>>
>>         memory_region_init(&vtd_dev_as->root, OBJECT(s),
>>                            "vtd_root", UINT64_MAX);
>>         address_space_init(&vtd_dev_as->as, &vtd_dev_as->root, name);
> 
> The problem is, I am not sure whether there is always _only_ one IOMMU
> region behind one device. E.g., IIUC ppc can have more than one IOMMU
> memory regions, but translate for different address ranges.
> 

If we really want to check this via memory region, we may check all
subregions under container's address space. Register vIOMMU related
notifiers if one of them has iommu_ops,


-- 
Best regards
Tianyu Lan