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

From: Lan Tianyu
Subject: Re: [Qemu-devel] [PATCH v2 7/7] intel_iommu: support passthrough (PT)
Date: Thu, 20 Apr 2017 15:10:54 +0800
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

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

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