[Intel-gfx] [PATCH v5 16/19] vfio: Add VFIO_DEVICE_BIND_IOMMUFD

[Alexey Kardashevskiy]

On 27/2/23 22:11, Yi Liu wrote:
> This adds ioctl for userspace to bind device cdev fd to iommufd.
> 
>      VFIO_DEVICE_BIND_IOMMUFD: bind device to an iommufd, hence gain DMA
> 			      control provided by the iommufd. open_device
> 			      op is called after bind_iommufd op.
> 			      VFIO no iommu mode is indicated by passing
> 			      a negative iommufd value.
> 
> Signed-off-by: Yi Liu <yi.l.liu at intel.com>
> ---
>   drivers/vfio/device_cdev.c | 146 +++++++++++++++++++++++++++++++++++++
>   drivers/vfio/vfio.h        |  17 ++++-
>   drivers/vfio/vfio_main.c   |  54 ++++++++++++--
>   include/linux/iommufd.h    |   6 ++
>   include/uapi/linux/vfio.h  |  34 +++++++++
>   5 files changed, 248 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> index 9e2c1ecaaf4f..37f80e368551 100644
> --- a/drivers/vfio/device_cdev.c
> +++ b/drivers/vfio/device_cdev.c
> @@ -3,6 +3,7 @@
>    * Copyright (c) 2023 Intel Corporation.
>    */
>   #include <linux/vfio.h>
> +#include <linux/iommufd.h>
>   
>   #include "vfio.h"
>   
> @@ -45,6 +46,151 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
>   	return ret;
>   }
>   
> +static void vfio_device_get_kvm_safe(struct vfio_device_file *df)
> +{
> +	spin_lock(&df->kvm_ref_lock);
> +	if (!df->kvm)
> +		goto unlock;
> +
> +	_vfio_device_get_kvm_safe(df->device, df->kvm);
> +
> +unlock:
> +	spin_unlock(&df->kvm_ref_lock);
> +}
> +
> +void vfio_device_cdev_close(struct vfio_device_file *df)
> +{
> +	struct vfio_device *device = df->device;
> +
> +	mutex_lock(&device->dev_set->lock);
> +	/*
> +	 * As df->access_granted writer is under dev_set->lock as well,
> +	 * so this read no need to use smp_load_acquire() to pair with
> +	 * smp_store_release() in the caller of vfio_device_open().
> +	 */
> +	if (!df->access_granted) {
> +		mutex_unlock(&device->dev_set->lock);
> +		return;
> +	}
> +	vfio_device_close(df);
> +	vfio_device_put_kvm(device);
> +	if (df->iommufd)
> +		iommufd_ctx_put(df->iommufd);
> +	mutex_unlock(&device->dev_set->lock);
> +	vfio_device_unblock_group(device);
> +}
> +
> +static struct iommufd_ctx *vfio_get_iommufd_from_fd(int fd)
> +{
> +	struct fd f;
> +	struct iommufd_ctx *iommufd;
> +
> +	f = fdget(fd);
> +	if (!f.file)
> +		return ERR_PTR(-EBADF);
> +
> +	iommufd = iommufd_ctx_from_file(f.file);
> +
> +	fdput(f);
> +	return iommufd;
> +}
> +
> +long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> +				    unsigned long arg)
> +{
> +	struct vfio_device *device = df->device;
> +	struct vfio_device_bind_iommufd bind;
> +	struct iommufd_ctx *iommufd = NULL;
> +	unsigned long minsz;
> +	int ret;
> +
> +	minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
> +
> +	if (copy_from_user(&bind, (void __user *)arg, minsz))
> +		return -EFAULT;
> +
> +	if (bind.argsz < minsz || bind.flags)
> +		return -EINVAL;
> +
> +	if (!device->ops->bind_iommufd)
> +		return -ENODEV;
> +
> +	ret = vfio_device_block_group(device);
> +	if (ret)
> +		return ret;
> +
> +	mutex_lock(&device->dev_set->lock);
> +	/*
> +	 * If already been bound to an iommufd, or already set noiommu
> +	 * then fail it.
> +	 */
> +	if (df->iommufd || df->noiommu) {
> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +
> +	/* iommufd < 0 means noiommu mode */
> +	if (bind.iommufd < 0) {
> +		if (!capable(CAP_SYS_RAWIO)) {
> +			ret = -EPERM;
> +			goto out_unlock;
> +		}
> +		df->noiommu = true;
> +	} else {
> +		iommufd = vfio_get_iommufd_from_fd(bind.iommufd);
> +		if (IS_ERR(iommufd)) {
> +			ret = PTR_ERR(iommufd);
> +			goto out_unlock;
> +		}
> +	}
> +
> +	/*
> +	 * Before the device open, get the KVM pointer currently
> +	 * associated with the device file (if there is) and obtain
> +	 * a reference.  This reference is held until device closed.
> +	 * Save the pointer in the device for use by drivers.
> +	 */
> +	vfio_device_get_kvm_safe(df);
> +
> +	df->iommufd = iommufd;
> +	ret = vfio_device_open(df, &bind.out_devid, NULL);


This is unrelated to this patch but reminded me - while debugging QEMU, 
vfio_assert_device_open() kept firing as I was killing QEMU (which in 
turn made the kernel close all fds), device->open_count==0 as QEMU was 
dying before calling ioctl(VFIO_DEVICE_BIND_IOMMUFD) which would call 
this vfio_device_open() just above. Has this been reported/fixed, just 
curious?



-- 
Alexey