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

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Message-ID: <ZkDZE32JFyKprmpi@nvidia.com>
Date: Sun, 12 May 2024 11:58:27 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...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 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;
};

> @@ -135,7 +135,16 @@ void iommufd_device_destroy(struct iommufd_object *obj)
>  {
>  	struct iommufd_device *idev =
>  		container_of(obj, struct iommufd_device, obj);
> +	struct iommufd_viommu *viommu;
> +	unsigned long index;
>  
> +	xa_for_each(&idev->viommus, index, viommu) {
> +		if (viommu->ops->unset_dev_id)
> +			viommu->ops->unset_dev_id(viommu, idev->dev);
> +		xa_erase(&viommu->idevs, idev->obj.id);
> +		xa_erase(&idev->viommus, index);
> +	}

Then this turns into list_for_each(idev->viommu_vdevid_list)

> +int iommufd_viommu_set_device_id(struct iommufd_ucmd *ucmd)
> +{
> +	struct iommu_viommu_set_dev_id *cmd = ucmd->cmd;
> +	unsigned int dev_id, viommu_id;
> +	struct iommufd_viommu *viommu;
> +	struct iommufd_device *idev;
> +	int rc;
> +
> +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> +	if (IS_ERR(idev))
> +		return PTR_ERR(idev);
> +	dev_id = idev->obj.id;
> +
> +	viommu = iommufd_get_viommu(ucmd, cmd->viommu_id);
> +	if (IS_ERR(viommu)) {
> +		rc = PTR_ERR(viommu);
> +		goto out_put_idev;
> +	}
> +
> +	if (viommu->iommu_dev != idev->dev->iommu->iommu_dev) {
> +		rc = -EINVAL;
> +		goto out_put_viommu;
> +	}
> +
> +	if (!viommu->ops->set_dev_id || !viommu->ops->unset_dev_id) {
> +		rc = -EOPNOTSUPP;
> +		goto out_put_viommu;
> +	}
> +
> +	rc = xa_alloc(&idev->viommus, &viommu_id, viommu,
> +		      XA_LIMIT(viommu->obj.id, viommu->obj.id),
> +		      GFP_KERNEL_ACCOUNT);
> +	if (rc)
> +		goto out_put_viommu;
> +
> +	rc = xa_alloc(&viommu->idevs, &dev_id, idev,
> +		      XA_LIMIT(dev_id, dev_id), GFP_KERNEL_ACCOUNT);
> +	if (rc)
> +		goto out_xa_erase_viommu;

Both of these are API mis-uses, you don't want an allocating xarray
you just want to use xa_cmpxchg

Put an xarray in the viommu object and fill it with pointers to the
struct dev_id thing above

The driver can piggyback on this xarray too if it wants, so we only
need one.

xa_cmpchg to install the user requests vdev_id only if the vdev_id is
already unused.

> @@ -51,6 +51,7 @@ enum {
>  	IOMMUFD_CMD_HWPT_GET_DIRTY_BITMAP,
>  	IOMMUFD_CMD_HWPT_INVALIDATE,
>  	IOMMUFD_CMD_VIOMMU_ALLOC,
> +	IOMMUFD_CMD_VIOMMU_SET_DEV_ID,
>  };

We almost certainly will need a REMOVE_DEV_ID so userspace can have
sensible error handling.

> +
> +/**
> + * struct iommu_viommu_set_dev_id - ioctl(IOMMU_VIOMMU_SET_DEV_ID)
> + * @size: sizeof(struct iommu_viommu_set_dev_id)
> + * @viommu_id: viommu ID to associate with the device to store its virtual ID
> + * @dev_id: device ID to set a device virtual ID
> + * @__reserved: Must be 0
> + * @id: Device virtual ID
> + *
> + * Set a viommu-specific virtual ID of a device
> + */
> +struct iommu_viommu_set_dev_id {
> +	__u32 size;
> +	__u32 viommu_id;
> +	__u32 dev_id;
> +	__u32 __reserved;
> +	__aligned_u64 id;

I think I'd consistently call this vdev_id throughout the API

Jason