linux-kernel - Re: [RFC 07/20] iommu/iommufd: Add iommufd_[un]bind

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Message-ID: <20210921171431.GT327412@nvidia.com>
Date:   Tue, 21 Sep 2021 14:14:31 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, hch@....de, jasowang@...hat.com,
        joro@...tes.org, jean-philippe@...aro.org, kevin.tian@...el.com,
        parav@...lanox.com, lkml@...ux.net, pbonzini@...hat.com,
        lushenming@...wei.com, eric.auger@...hat.com, corbet@....net,
        ashok.raj@...el.com, yi.l.liu@...ux.intel.com,
        jun.j.tian@...el.com, hao.wu@...el.com, dave.jiang@...el.com,
        jacob.jun.pan@...ux.intel.com, kwankhede@...dia.com,
        robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        david@...son.dropbear.id.au, nicolinc@...dia.com
Subject: Re: [RFC 07/20] iommu/iommufd: Add iommufd_[un]bind_device()

On Sun, Sep 19, 2021 at 02:38:35PM +0800, Liu Yi L wrote:

> +/*
> + * A iommufd_device object represents the binding relationship
> + * between iommufd and device. It is created per a successful
> + * binding request from device driver. The bound device must be
> + * a physical device so far. Subdevice will be supported later
> + * (with additional PASID information). An user-assigned cookie
> + * is also recorded to mark the device in the /dev/iommu uAPI.
> + */
> +struct iommufd_device {
> +	unsigned int id;
> +	struct iommufd_ctx *ictx;
> +	struct device *dev; /* always be the physical device */
> +	u64 dev_cookie;
>  };
>  
>  static int iommufd_fops_open(struct inode *inode, struct file *filep)
> @@ -32,15 +52,58 @@ static int iommufd_fops_open(struct inode *inode, struct file *filep)
>  		return -ENOMEM;
>  
>  	refcount_set(&ictx->refs, 1);
> +	mutex_init(&ictx->lock);
> +	xa_init_flags(&ictx->device_xa, XA_FLAGS_ALLOC);
>  	filep->private_data = ictx;
>  
>  	return ret;
>  }
>  
> +static void iommufd_ctx_get(struct iommufd_ctx *ictx)
> +{
> +	refcount_inc(&ictx->refs);
> +}

See my earlier remarks about how to structure the lifetime logic, this
ref isn't necessary.

> +static const struct file_operations iommufd_fops;
> +
> +/**
> + * iommufd_ctx_fdget - Acquires a reference to the internal iommufd context.
> + * @fd: [in] iommufd file descriptor.
> + *
> + * Returns a pointer to the iommufd context, otherwise NULL;
> + *
> + */
> +static struct iommufd_ctx *iommufd_ctx_fdget(int fd)
> +{
> +	struct fd f = fdget(fd);
> +	struct file *file = f.file;
> +	struct iommufd_ctx *ictx;
> +
> +	if (!file)
> +		return NULL;
> +
> +	if (file->f_op != &iommufd_fops)
> +		return NULL;

Leaks the fdget

> +
> +	ictx = file->private_data;
> +	if (ictx)
> +		iommufd_ctx_get(ictx);

Use success oriented flow

> +	fdput(f);
> +	return ictx;
> +}

> + */
> +struct iommufd_device *iommufd_bind_device(int fd, struct device *dev,
> +					   u64 dev_cookie)
> +{
> +	struct iommufd_ctx *ictx;
> +	struct iommufd_device *idev;
> +	unsigned long index;
> +	unsigned int id;
> +	int ret;
> +
> +	ictx = iommufd_ctx_fdget(fd);
> +	if (!ictx)
> +		return ERR_PTR(-EINVAL);
> +
> +	mutex_lock(&ictx->lock);
> +
> +	/* check duplicate registration */
> +	xa_for_each(&ictx->device_xa, index, idev) {
> +		if (idev->dev == dev || idev->dev_cookie == dev_cookie) {
> +			idev = ERR_PTR(-EBUSY);
> +			goto out_unlock;
> +		}

I can't think of a reason why this expensive check is needed.

> +	}
> +
> +	idev = kzalloc(sizeof(*idev), GFP_KERNEL);
> +	if (!idev) {
> +		ret = -ENOMEM;
> +		goto out_unlock;
> +	}
> +
> +	/* Establish the security context */
> +	ret = iommu_device_init_user_dma(dev, (unsigned long)ictx);
> +	if (ret)
> +		goto out_free;
> +
> +	ret = xa_alloc(&ictx->device_xa, &id, idev,
> +		       XA_LIMIT(IOMMUFD_DEVID_MIN, IOMMUFD_DEVID_MAX),
> +		       GFP_KERNEL);

idev should be fully initialized before being placed in the xarray, so
this should be the last thing done.

Why not just use the standard xa_limit_32b instead of special single
use constants?

Jason