RE: [PATCH v5 16/19] vfio: Add VFIO_DEVICE_BIND_IOMMUFD

Liu, Yi L
2023-02-28T04:09:00Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, February 28, 2023 3:20 AM
>
> On Mon, Feb 27, 2023 at 03:11:32AM -0800, 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@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:
>
> Just
>
> if (df->kvm)
> _vfio_device_get_kvm_safe(df->device, df->kvm);
>
> Without the goto

Got it.

> > + 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().
> > + */
>
> This is a bit misleading, we are about to free df in the caller, so at
> this moment df has no current access. We don't even need to have the
> mutex to test it.

Ok. so I can test it outside the lock and make the comment
more clear? How about below? Or simply no need to have
a comment here?

/*
* caller of vfio_device_cdev_close() is going to free df, so there
* is no need to use smp_load_acquire() to pair with
* smp_store_release() in the writer path of df->access_granted.
*/

> > +long vfio_device_ioctl_bind_iommufd(struct vfio_device_file *df,
> > + unsigned long arg)
>
> struct device __user *arg and remove all the casts.
>
> > +{
> > + 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);
> > + if (ret)
> > + goto out_put_kvm;
> > +
> > + ret = copy_to_user((void __user *)arg +
> > + offsetofend(struct vfio_device_bind_iommufd,
> iommufd),
>
> ??
>
> &arg->out_dev_id
>
> static_assert(__same_type...)

Yes, all the above comments are similar with other two patches. Will
refine accordingly.

> > diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
> > index 650d45629647..9672cf839687 100644
> > --- a/include/linux/iommufd.h
> > +++ b/include/linux/iommufd.h
> > @@ -17,6 +17,12 @@ struct iommufd_ctx;
> > struct iommufd_access;
> > struct file;
> >
> > +/*
> > + * iommufd core init xarray with flags==XA_FLAGS_ALLOC1, so valid
> > + * ID starts from 1.
> > + */
> > +#define IOMMUFD_INVALID_ID 0
>
> Why? vfio doesn't need to check this just to generate EINVAL.

Hmmm, you are right. Not needed any more.

Regards,
Yi Liu