linux-kernel - Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ

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Message-ID: <7c813df6-e37d-47ae-9b5a-b8735c865626@amd.com>
Date: Wed, 30 Apr 2025 09:52:09 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Nicolin Chen <nicolinc@...dia.com>, jgg@...dia.com, kevin.tian@...el.com
Cc: corbet@....net, will@...nel.org, bagasdotme@...il.com,
 robin.murphy@....com, joro@...tes.org, thierry.reding@...il.com,
 vdumpa@...dia.com, jonathanh@...dia.com, shuah@...nel.org,
 jsnitsel@...hat.com, nathan@...nel.org, peterz@...radead.org,
 yi.l.liu@...el.com, mshavit@...gle.com, praan@...gle.com,
 zhangzekun11@...wei.com, iommu@...ts.linux.dev, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-tegra@...r.kernel.org, linux-kselftest@...r.kernel.org,
 patches@...ts.linux.dev, mochs@...dia.com, alok.a.tiwari@...cle.com,
 Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ_ALLOC
 ioctl

Hi Nicolin,


On 4/29/2025 10:44 PM, Nicolin Chen wrote:
> On Tue, Apr 29, 2025 at 03:52:48PM +0530, Vasant Hegde wrote:
>> On 4/29/2025 12:15 PM, Nicolin Chen wrote:
>>> On Tue, Apr 29, 2025 at 11:04:06AM +0530, Vasant Hegde wrote:
>>>> On 4/29/2025 1:32 AM, Nicolin Chen wrote:
>>>>> On Mon, Apr 28, 2025 at 05:42:27PM +0530, Vasant Hegde wrote:
>>>>> Yes. For AMD "vIOMMU", it needs a new type for iommufd vIOMMU:
>>>>> 	IOMMU_VIOMMU_TYPE_AMD_VIOMMU,
>>>>>
>>>>> For AMD "vIOMMU" command buffer, it needs a new type too:
>>>>> 	IOMMU_VCMDQ_TYPE_AMD_VIOMMU, /* Kdoc it to be Command Buffer */
>>>>
>>>> You are suggesting we define one type for AMD and use it for all buffers like
>>>> command buffer, event log, PPR buffet etc? and use iommu_vcmdq_alloc->index to
>>>> identity different buffer type?
>>>
>>> We have vEVENTQ for event logging and FAULT_QUEUE for PRI, but both
>>> are not for hardware accelerated use cases.
>>>
>>> I didn't check the details of AMD's event log and PPR buffers. But
>>> they seem to be the same ring buffers and can be consumed by guest
>>> kernel directly?
>>
>> Right. Event log is accelerated and consumed by guest directly. Also we have
>> Event Log B !
>>
>>>
>>> Will the hardware replace the physical device ID in the event with
>>> the virtual device ID when injecting the event to a guest event/PPR
>>> queue? 
>>> If so, yea, I think you can define them separately using the> vCMDQ
>> infrastructures:
>>>  - IOMMU_VCMDQ_TYPE_AMD_VIOMMU_CMDBUF
>>>  - IOMMU_VCMDQ_TYPE_AMD_VIOMMU_EVENTLOG
>>>  - IOMMU_VCMDQ_TYPE_AMD_VIOMMU_PPRLOG
>>> (@Kevin @Jason Hmm, in this case we might want to revert the naming
>>>  "vCMDQ" back to "vQEUEUE", once Vasant confirms.)
> 
> I think I should rename IOMMUFD_OBJ_VCMDQ back to IOMMUFD_OBJ_VQUEUE
> since the same object fits three types of queue now in the AMD case.

Makes sense.

AMD architecture supports 5 buffers. In practice we have not implemented event
log  B / PPR Log B in Linux.
  Command buffer
  Event Log A / B
  PPR Log A / B


-Vasant