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

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Message-ID: <487ebe2c-718f-405c-8f20-213eab59ca0f@amd.com>
Date: Fri, 25 Oct 2024 16:32:10 +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 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?

> https://lore.kernel.org/linux-iommu/ZxsSYbK3gqyC84U7@Asurada-Nvidia/
> https://lore.kernel.org/linux-iommu/ZxsTAANTTuQzQ9HR@Asurada-Nvidia/
> 
> Do you need vdevice_alloc in the driver for your sketch?

At the moment one of the things I am looking for is a place to add 
tsm_bind(host_bdfn, guest_bdfn, kvm_vmid). I assumed that this vdevice 
represents the guest's IOMMU attributes for a passed through device and 
naturally stores the guest_bdfn as an id (for AMD). I am still trying to 
wrap my head around these new things. Thanks,


-- 
Alexey