linux-kernel - Re: [PATCH v4 00/14] iommufd: Add vIOMMU infrastructure (Part-2: vDEVICE)

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Message-ID: <607d019e-25b7-45b8-8c85-3829d4b53a82@amd.com>
Date: Fri, 25 Oct 2024 16:58:33 +1100
From: Alexey Kardashevskiy <aik@....com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, will@...nel.org, joro@...tes.org,
 suravee.suthikulpanit@....com, robin.murphy@....com, dwmw2@...radead.org,
 baolu.lu@...ux.intel.com, shuah@...nel.org, linux-kernel@...r.kernel.org,
 iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
 jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
 shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
 yi.l.liu@...el.com, zhangfei.gao@...aro.org, patches@...ts.linux.dev
Subject: Re: [PATCH v4 00/14] iommufd: Add vIOMMU infrastructure (Part-2:
 vDEVICE)



On 25/10/24 16:41, Nicolin Chen wrote:
> On Fri, Oct 25, 2024 at 04:32:10PM +1100, Alexey Kardashevskiy wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 25/10/24 15:59, Nicolin Chen wrote:
>>> On Fri, Oct 25, 2024 at 03:54:44PM +1100, Alexey Kardashevskiy wrote:
>>>> On 22/10/24 11:20, Nicolin Chen wrote:
>>>>> Following the previous vIOMMU series, this adds another vDEVICE structure,
>>>>> representing the association from an iommufd_device to an iommufd_viommu.
>>>>> This gives the whole architecture a new "v" layer:
>>>>>      _______________________________________________________________________
>>>>>     |                      iommufd (with vIOMMU/vDEVICE)                    |
>>>>>     |                        _____________      _____________               |
>>>>>     |                       |             |    |             |              |
>>>>>     |      |----------------|    vIOMMU   |<---|   vDEVICE   |<------|      |
>>>>>     |      |                |             |    |_____________|       |      |
>>>>>     |      |     ______     |             |     _____________     ___|____  |
>>>>>     |      |    |      |    |             |    |             |   |        | |
>>>>>     |      |    | IOAS |<---|(HWPT_PAGING)|<---| HWPT_NESTED |<--| DEVICE | |
>>>>>     |      |    |______|    |_____________|    |_____________|   |________| |
>>>>>     |______|________|______________|__________________|_______________|_____|
>>>>>            |        |              |                  |               |
>>>>>      ______v_____   |        ______v_____       ______v_____       ___v__
>>>>>     |   struct   |  |  PFN  |  (paging)  |     |  (nested)  |     |struct|
>>>>>     |iommu_device|  |------>|iommu_domain|<----|iommu_domain|<----|device|
>>>>>     |____________|   storage|____________|     |____________|     |______|
>>>>>
>>>>> This vDEVICE object is used to collect and store all vIOMMU-related device
>>>>> information/attributes in a VM. As an initial series for vDEVICE, add only
>>>>> the virt_id to the vDEVICE, which is a vIOMMU specific device ID in a VM:
>>>>> e.g. vSID of ARM SMMUv3, vDeviceID of AMD IOMMU, and vID of Intel VT-d to
>>>>> a Context Table. This virt_id helps IOMMU drivers to link the vID to a pID
>>>>> of the device against the physical IOMMU instance. This is essential for a
>>>>> vIOMMU-based invalidation, where the request contains a device's vID for a
>>>>> device cache flush, e.g. ATC invalidation.
>>>>>
>>>>> Therefore, with this vDEVICE object, support a vIOMMU-based invalidation,
>>>>> by reusing IOMMUFD_CMD_HWPT_INVALIDATE for a vIOMMU object to flush cache
>>>>> with a given driver data.
>>>>>
>>>>> As for the implementation of the series, add driver support in ARM SMMUv3
>>>>> for a real world use case.
>>>>>
>>>>> This series is on Github:
>>>>> https://github.com/nicolinc/iommufd/commits/iommufd_viommu_p2-v4
>>>>>
>>>>> For testing, try this "with-rmr" branch:
>>>>> https://github.com/nicolinc/iommufd/commits/iommufd_viommu_p2-v4-with-rmr
>>>>
>>>> Is there any real example of a .vdevice_alloc hook, besides the
>>>> selftests? It is not in iommufd_viommu_p2-v4-with-rmr, hence the
>>>> question. I am trying to sketch something with this new machinery and
>>>> less guessing would be nice. Thanks,
>>>
>>> No, I am actually dropping that one, and moving the vdevice struct
>>> to the private header, as there seems to be no use case:
>>
>> Why keep it then?
> 
> We need that structure to store per-vIOMMU virtual ID. Hiding it
> in the core only means we need to provide another vIOMMU APIs for
> drivers to look up the ID, v.s. exposing it for drivers to access
> directly.

Sorry I lost you here. If we need it, then there should be an example of 
.vdevice_alloc() somewhere but you say they is not one. How do you test 
this, with just selftests? :) Thanks,


> 
> Thanks
> Nicolin

-- 
Alexey