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

Liu, Yi L
2023-05-23T01:41:49Z

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Tuesday, May 23, 2023 6:01 AM
>
> On Sat, 13 May 2023 06:28:23 -0700
> Yi Liu <yi.l.liu@intel.com> 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@intel.com>
> > Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> > Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> > ---
> > 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