Re: [PATCH v11 19/23] vfio: Add VFIO_DEVICE_BIND_IOMMUFD

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> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Tuesday, May 23, 2023 6:01 AM
> 
> On Sat, 13 May 2023 06:28:23 -0700
> Yi Liu <yi.l.liu@xxxxxxxxx> 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.
> >
> > Tested-by: Yanting Jiang <yanting.jiang@xxxxxxxxx>
> > Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> >  drivers/vfio/device_cdev.c | 130 +++++++++++++++++++++++++++++++++++++
> >  drivers/vfio/vfio.h        |  13 ++++
> >  drivers/vfio/vfio_main.c   |   5 ++
> >  include/linux/vfio.h       |   3 +-
> >  include/uapi/linux/vfio.h  |  28 ++++++++
> >  5 files changed, 178 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> > index 1c640016a824..291cc678a18b 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"
> >
> > @@ -44,6 +45,135 @@ 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)
> > +		_vfio_device_get_kvm_safe(df->device, df->kvm);
> > +	spin_unlock(&df->kvm_ref_lock);
> > +}
> > +
> > +void vfio_device_cdev_close(struct vfio_device_file *df)
> > +{
> > +	struct vfio_device *device = df->device;
> > +
> > +	/*
> > +	 * In the time of close, there is no contention with another one
> > +	 * changing this flag.  So read df->access_granted without lock
> > +	 * and no smp_load_acquire() is ok.
> > +	 */
> > +	if (!df->access_granted)
> > +		return;
> > +
> > +	mutex_lock(&device->dev_set->lock);
> > +	vfio_device_close(df);
> > +	vfio_device_put_kvm(device);
> > +	iommufd_ctx_put(df->iommufd);
> > +	device->cdev_opened = false;
> > +	mutex_unlock(&device->dev_set->lock);
> > +	vfio_device_unblock_group(device);
> > +}
> > +
> > +static struct iommufd_ctx *vfio_get_iommufd_from_fd(int fd)
> > +{
> > +	struct iommufd_ctx *iommufd;
> > +	struct fd f;
> > +
> > +	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,
> > +				    struct vfio_device_bind_iommufd __user *arg)
> > +{
> > +	struct vfio_device *device = df->device;
> > +	struct vfio_device_bind_iommufd bind;
> > +	unsigned long minsz;
> > +	int ret;
> > +
> > +	static_assert(__same_type(arg->out_devid, df->devid));
> > +
> > +	minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
> > +
> > +	if (copy_from_user(&bind, arg, minsz))
> > +		return -EFAULT;
> > +
> > +	if (bind.argsz < minsz || bind.flags || bind.iommufd < 0)
> > +		return -EINVAL;
> > +
> > +	/* BIND_IOMMUFD only allowed for cdev fds */
> > +	if (df->group)
> > +		return -EINVAL;
> > +
> > +	if (vfio_device_is_noiommu(device) && !capable(CAP_SYS_RAWIO))
> > +		return -EPERM;
> > +
> > +	ret = vfio_device_block_group(device);
> > +	if (ret)
> > +		return ret;
> > +
> > +	mutex_lock(&device->dev_set->lock);
> > +	/* one device cannot be bound twice */
> > +	if (df->access_granted) {
> > +		ret = -EINVAL;
> > +		goto out_unlock;
> > +	}
> > +
> > +	df->iommufd = vfio_get_iommufd_from_fd(bind.iommufd);
> > +	if (IS_ERR(df->iommufd)) {
> > +		ret = PTR_ERR(df->iommufd);
> > +		df->iommufd = NULL;
> > +		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);
> > +
> > +	ret = vfio_device_open(df);
> > +	if (ret)
> > +		goto out_put_kvm;
> > +
> > +	ret = copy_to_user(&arg->out_devid, &df->devid,
> > +			   sizeof(df->devid)) ? -EFAULT : 0;
> > +	if (ret)
> > +		goto out_close_device;
> > +
> > +	/*
> > +	 * Paired with smp_load_acquire() in vfio_device_fops::ioctl/
> > +	 * read/write/mmap
> > +	 */
> > +	smp_store_release(&df->access_granted, true);
> > +	device->cdev_opened = true;
> > +	mutex_unlock(&device->dev_set->lock);
> > +
> > +	if (vfio_device_is_noiommu(device))
> > +		dev_warn(device->dev, "noiommu device is bound to iommufd by user
> "
> > +			 "(%s:%d)\n", current->comm, task_pid_nr(current));
> 
> The noiommu kernel taint only happens in vfio_group_find_or_alloc(), so
> how does noiommu taint the kernel when !CONFIG_VFIO_GROUP?

Yeah, in the cdev path, no taint. I add this just in order to par with the below
message in the group path.

vfio_device_open_file()
{
	dev_warn(device->dev, "vfio-noiommu device opened by user "
		   "(%s:%d)\n", current->comm, task_pid_nr(current));
}

> > +	return 0;
> > +
> > +out_close_device:
> > +	vfio_device_close(df);
> > +out_put_kvm:
> > +	vfio_device_put_kvm(device);
> > +	iommufd_ctx_put(df->iommufd);
> > +	df->iommufd = NULL;
> > +out_unlock:
> > +	mutex_unlock(&device->dev_set->lock);
> > +	vfio_device_unblock_group(device);
> > +	return ret;
> > +}
> > +
> >  static char *vfio_device_devnode(const struct device *dev, umode_t *mode)
> >  {
> >  	return kasprintf(GFP_KERNEL, "vfio/devices/%s", dev_name(dev));
> > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> > index 6861f8ebb64d..8b359a7794be 100644
> > --- a/drivers/vfio/vfio.h
> > +++ b/drivers/vfio/vfio.h
> > @@ -279,6 +279,9 @@ static inline void vfio_device_del(struct vfio_device *device)
> >
> >  void vfio_init_device_cdev(struct vfio_device *device);
> >  int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep);
> > +void vfio_device_cdev_close(struct vfio_device_file *df);
> > +long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> > +				    struct vfio_device_bind_iommufd __user *arg);
> >  int vfio_cdev_init(struct class *device_class);
> >  void vfio_cdev_cleanup(void);
> >  #else
> > @@ -302,6 +305,16 @@ static inline int vfio_device_fops_cdev_open(struct inode
> *inode,
> >  	return 0;
> >  }
> >
> > +static inline void vfio_device_cdev_close(struct vfio_device_file *df)
> > +{
> > +}
> > +
> > +static inline long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> > +						  struct vfio_device_bind_iommufd
> __user *arg)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >  static inline int vfio_cdev_init(struct class *device_class)
> >  {
> >  	return 0;
> > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> > index c87cc7afe92c..c9fa39ac4b02 100644
> > --- a/drivers/vfio/vfio_main.c
> > +++ b/drivers/vfio/vfio_main.c
> > @@ -574,6 +574,8 @@ static int vfio_device_fops_release(struct inode *inode, struct
> file *filep)
> >
> >  	if (df->group)
> >  		vfio_device_group_close(df);
> > +	else
> > +		vfio_device_cdev_close(df);
> >
> >  	vfio_device_put_registration(device);
> >
> > @@ -1147,6 +1149,9 @@ static long vfio_device_fops_unl_ioctl(struct file *filep,
> >  	struct vfio_device *device = df->device;
> >  	int ret;
> >
> > +	if (cmd == VFIO_DEVICE_BIND_IOMMUFD)
> > +		return vfio_device_ioctl_bind_iommufd(df, (void __user *)arg);
> > +
> >  	/* Paired with smp_store_release() following vfio_device_open() */
> >  	if (!smp_load_acquire(&df->access_granted))
> >  		return -EINVAL;
> > diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> > index 873275419f13..cf9d082a623c 100644
> > --- a/include/linux/vfio.h
> > +++ b/include/linux/vfio.h
> > @@ -67,6 +67,7 @@ struct vfio_device {
> >  	struct iommufd_device *iommufd_device;
> >  	bool iommufd_attached;
> >  #endif
> > +	bool cdev_opened:1;
> >  };
> >
> >  /**
> > @@ -169,7 +170,7 @@ vfio_iommufd_physical_devid(struct vfio_device *vdev)
> >
> >  static inline bool vfio_device_cdev_opened(struct vfio_device *device)
> >  {
> > -	return false;
> > +	return device->cdev_opened;
> >  }
> >
> >  /**
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 24858b650562..07c917de31e9 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -194,6 +194,34 @@ struct vfio_group_status {
> >
> >  /* --------------- IOCTLs for DEVICE file descriptors --------------- */
> >
> > +/*
> > + * VFIO_DEVICE_BIND_IOMMUFD - _IOR(VFIO_TYPE, VFIO_BASE + 19,
> > + *				   struct vfio_device_bind_iommufd)
> > + *
> > + * Bind a vfio_device to the specified iommufd.
> > + *
> > + * User is restricted from accessing the device before the binding operation
> > + * is completed.
> > + *
> > + * Unbind is automatically conducted when device fd is closed.
> > + *
> > + * @argsz:	 User filled size of this data.
> > + * @flags:	 Must be 0.
> > + * @iommufd:	 iommufd to bind.
> > + * @out_devid:	 The device id generated by this bind. devid is a handle for
> > + *		 this device/iommufd bond and can be used in IOMMUFD commands.
> > + *
> > + * Return: 0 on success, -errno on failure.
> > + */
> > +struct vfio_device_bind_iommufd {
> > +	__u32		argsz;
> > +	__u32		flags;
> > +	__s32		iommufd;
> > +	__u32		out_devid;
> > +};
> > +
> > +#define VFIO_DEVICE_BIND_IOMMUFD	_IO(VFIO_TYPE, VFIO_BASE + 19)
> > +
> 
> Why is this preempting the first device ioctl below rather than being
> added in sequential order?  I'm also not sure what's at device ioctl 18
> that we started at 19.  VFIO_DEVICE_FEATURE is at 17.  Yes, they're
> hard to keep track of.  Thanks,

yes, 17 is the last occupied ioctl offset on device fd. Will correct
it.

Regards,
Yi Liu




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