linux-kernel - Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV

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Date: Sun, 12 May 2024 22:24:13 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <will@...nel.org>, <robin.murphy@....com>, <kevin.tian@...el.com>,
	<suravee.suthikulpanit@....com>, <joro@...tes.org>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<yi.l.liu@...el.com>, <eric.auger@...hat.com>, <vasant.hegde@....com>,
	<jon.grimm@....com>, <santosh.shukla@....com>, <Dhaval.Giani@....com>,
	<shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl

On Sun, May 12, 2024 at 11:58:27AM -0300, Jason Gunthorpe wrote:
> On Fri, Apr 12, 2024 at 08:47:05PM -0700, Nicolin Chen wrote:
> > Introduce a new ioctl to set a per-viommu device virtual id that should be
> > linked to the physical device id (or just a struct device pointer).
> > 
> > Since a viommu (user space IOMMU instance) can have multiple devices while
> > it's not ideal to confine a device to one single user space IOMMU instance
> > either, these two shouldn't just do a 1:1 mapping. Add two xarrays in their
> > structures to bind them bidirectionally.
> 
> Since I would like to retain the dev_id, I think this is probably
> better done with an allocated struct per dev-id:
> 
> struct dev_id {
>     struct iommufd_device *idev;
>     struct iommufd_viommu *viommu;
>     u64 vdev_id;
>     u64 driver_private; // Ie the driver can store the pSID here
>     struct list_head idev_entry;
> };

Oh, I needed a better solution to store the HW slot number of a
VINTF configuration that links a pSID and a vSID, which I hacked
into struct arm_smmu_stream for now. So, with this struct dev_id,
likely I can tie it to this structure.

For a driver, pSID is known with a device pointer, while likely
no use to the iommufd core?

Also, I will address the other comments in your reply.

Thanks
Nicolin