linux-kernel - Re: [PATCH v3 11/23] iommufd/viommu: Add IOMMUFD_CMD_VQUEUE

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Message-ID: <20250508121456.GB5657@nvidia.com>
Date: Thu, 8 May 2025 09:14:56 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Vasant Hegde <vasant.hegde@....com>, kevin.tian@...el.com,
	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 v3 11/23] iommufd/viommu: Add IOMMUFD_CMD_VQUEUE_ALLOC
 ioctl

On Wed, May 07, 2025 at 10:56:17PM -0700, Nicolin Chen wrote:

> What I am not sure is if the HW allows setting the ComWaitIntEn bit
> after CmdBufEn=1, which seems to be unlikely but the spec does not
> highlight. If so, this would be an modification to the HW QUEUE, in
> which case we could either do an relocation of the HW QUEUE (where
> we can set the flag in the 2nd allocation) or add an new option via
> IOMMUFD_CMD_OPTION (as Kevin suggested), and I think it should be
> a per-HW_QUEUE option since it doesn't affect other type of queues
> like Event/PRR Log Buffers.

The main question is if the control is global to the entire VIOMMU and
all its HW QUEUE's or local to a single HW QUEUE.

If it is global then some "modify viommu" operation should be used to
change it.

If it is local then some "modify hw queu" operation.

IOMMUFD_CMD_OPTION could be used with an object_id == VIOMMU as a kind
of modify..

Jason