linux-kernel - Re: [PATCH v2 02/22] iommu: Pass in a driver-level user data structure to viommu

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Message-ID: <aA-6zlZNQ6NsrUqw@google.com>
Date: Mon, 28 Apr 2025 17:28:46 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Baolu Lu <baolu.lu@...ux.intel.com>, jgg@...dia.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,
	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, vasant.hegde@....com
Subject: Re: [PATCH v2 02/22] iommu: Pass in a driver-level user data
 structure to viommu_alloc op

On Mon, Apr 28, 2025 at 10:19:21AM -0700, Nicolin Chen wrote:
> On Sun, Apr 27, 2025 at 02:31:54PM +0800, Baolu Lu wrote:
> > On 4/26/25 13:57, Nicolin Chen wrote:
> > > The new type of vIOMMU for tegra241-cmdqv needs to pass in a driver-level
> > > data structure from user space via iommufd, so add a user_data to the op.
> > > 
> > > Reviewed-by: Jason Gunthorpe<jgg@...dia.com>
> > > Signed-off-by: Nicolin Chen<nicolinc@...dia.com>
> > 
> > It would be better to add some words explaining what kind of user data
> > can be passed when allocating a vIOMMU object and the reason why this
> > might be necessary.
> > 
> > Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> 
> Sure. Will do something like this:
> 
> The new type of vIOMMU for tegra241-cmdqv allows user space VM to use one
> of its virtual command queue HW resources exclusively. This requires user
> space to mmap the corresponding MMIO page from kernel space for direct HW
> control.
> 
> To forward the mmap info (vm_pgoff and size), iommufd should add a driver
> specific data structure to the IOMMUFD_CMD_VIOMMU_ALLOC ioctl, for driver
> to output the info (during the allocation) back to user space.
> 
> Similar to the existing ioctls and their IOMMU handlers, add a user_data
> to viommu_alloc op to bridge between iommufd and drivers.
> 

Ack, with this change (addressing Lu's nit).

Reviewed-by: Pranjal Shrivastava <praan@...gle.com>

> Thanks
> Nicolin