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

Alexey Kardashevskiy
2023-03-10T02:39:34Z

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@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