> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Thursday, March 30, 2023 5:01 AM
>
> On Mon, 27 Mar 2023 02:40:44 -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.
> > VFIO no iommu mode is indicated by passing
> > a negative iommufd value.
> >
> > Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Tested-by: Terrence Xu <terrence.xu@xxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> > drivers/vfio/device_cdev.c | 153 +++++++++++++++++++++++++++++++++++++
> > drivers/vfio/vfio.h | 13 ++++
> > drivers/vfio/vfio_main.c | 5 ++
> > include/uapi/linux/vfio.h | 37 +++++++++
> > 4 files changed, 208 insertions(+)
> >
> > diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> > index 1c640016a824..2b563bac50b9 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 +45,158 @@ 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;
> > +
> > + /*
> > + * 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
>
> Nit, "no need to use" -> "does not need to use"
got it.
>
> > + * smp_store_release() in the caller of vfio_device_open().
> > + */
> > + if (!df->access_granted)
> > + return;
> > +
>
> Isn't the lock we're acquiring below the one that we claim to have in
> the comment above to make the non-smp_load_acquire() test safe?
the comment may be not accurate enough. The the non-smp_load_acquire()
and no lock test were according to the below two remarks in v4 and v5.
https://lore.kernel.org/kvm/Y%2FYRx7jLuyEoLxZg@xxxxxxxxxx/
https://lore.kernel.org/kvm/Y%2F0CV1K0YNHA+olf@xxxxxxxxxx/
Perhaps the comment should be:
"In the time of close, there is no contention with another one
changing this flag. So test df->access_granted without lock
nor smp_load_acquire() is ok."
> > + mutex_lock(&device->dev_set->lock);
> > + 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 int vfio_device_cdev_enable_noiommu(struct vfio_device *device)
> > +{
> > + if (!capable(CAP_SYS_RAWIO))
> > + return -EPERM;
> > +
> > + if (!device->noiommu)
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
>
> This is testing, not enabling. ie. naming nit.
how about probe_noiommu or test_noiommu?
>
> > +
> > +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,
> > + struct vfio_device_bind_iommufd __user *arg)
> > +{
> > + struct vfio_device *device = df->device;
> > + struct vfio_device_bind_iommufd bind;
> > + struct iommufd_ctx *iommufd = NULL;
> > + unsigned long minsz;
> > + int ret;
> > +
> > + static_assert(__same_type(arg->out_devid, bind.out_devid));
>
> They're the same field in the same structure, how could they be
> otherwise?
@Jason, should I remove this check?
> > +
> > + minsz = offsetofend(struct vfio_device_bind_iommufd, out_devid);
> > +
> > + if (copy_from_user(&bind, arg, minsz))
> > + return -EFAULT;
> > +
> > + if (bind.argsz < minsz || bind.flags)
> > + return -EINVAL;
> > +
> > + if (!device->ops->bind_iommufd)
> > + return -ENODEV;
>
> This test seems beyond normal paranoia since we test in
> __vfio_register_dev()
yes. The whole c file depends on VFIO_DEVICE_CDEV which
depends on IOMMUFD, and if IOMMUFD is enabled,
__vfio_register_dev() already checks this callback.
>
> > +
> > + /* BIND_IOMMUFD only allowed for cdev fds */
> > + if (df->group)
> > + return -EINVAL;
> > +
> > + 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;
> > + }
> > +
> > + /* iommufd < 0 means noiommu mode */
> > + if (bind.iommufd < 0) {
> > + ret = vfio_device_cdev_enable_noiommu(device);
> > + if (ret)
> > + goto out_unlock;
> > + } 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);
> > + if (ret)
> > + goto out_put_kvm;
> > +
> > + if (df->iommufd)
> > + bind.out_devid = df->devid;
>
> How about only setting df->iommufd in the non-noiommu case above so
> it's not confusing that it was just set 4 lines previous. That also
> allows the iommufd pointer to be scoped within that branch and not
> require initialization. It might make sense to declare:
>
> bool is_noiommu = (bind.iommufd < 0);
>
> and use it consistently rather than alternating testing between
> bind.iommufd and df->iommufd.
sure.
> > +
> > + ret = copy_to_user(&arg->out_devid, &bind.out_devid,
> > + sizeof(bind.out_devid)) ? -EFAULT : 0;
>
> In the noiommu case, this copies back the input value, shouldn't it be
> some known invalid value? Seems confusing.
maybe just do copy for the non-noiommu case?
> > + if (ret)
> > + goto out_close_device;
> > +
> > + if (bind.iommufd < 0)
> > + dev_warn(device->dev, "device is bound to vfio-noiommu by user "
> > + "(%s:%d)\n", current->comm, task_pid_nr(current));
> > +
> > + /*
> > + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/
> > + * read/write/mmap
> > + */
> > + smp_store_release(&df->access_granted, true);
> > + mutex_unlock(&device->dev_set->lock);
> > +
> > + return 0;
> > +
> > +out_close_device:
> > + vfio_device_close(df);
> > +out_put_kvm:
> > + df->iommufd = NULL;
> > + vfio_device_put_kvm(device);
> > + if (iommufd)
> > + iommufd_ctx_put(iommufd);
> > +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 3a8fd0e32f59..ace3d52b0928 100644
> > --- a/drivers/vfio/vfio.h
> > +++ b/drivers/vfio/vfio.h
> > @@ -281,6 +281,9 @@ 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
> > @@ -304,6 +307,16 @@ 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 58fc3bb768f2..375086c8803f 100644
> > --- a/drivers/vfio/vfio_main.c
> > +++ b/drivers/vfio/vfio_main.c
> > @@ -559,6 +559,8 @@ 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);
> >
> > @@ -1132,6 +1134,9 @@ 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/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 61b801dfd40b..62b2f2497525 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -194,6 +194,43 @@ 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.
> > + *
> > + * The user should provide a device cookie when calling this ioctl. The
> > + * cookie is carried only in event e.g. I/O fault reported to userspace
> > + * via iommufd. The user should use devid returned by this ioctl to mark
> > + * the target device in other ioctls (e.g. iommu hardware infomration query
> > + * via iommufd, and etc.).
>
> AFAICT, the whole concept of this dev_cookie is a fantasy. It only
> exists in this series in these comments and the structure below. It's
> not even defined whether it needs to be unique within an iommufd
> context, and clearly nothing here validates that. There's not enough
> implementation for it to exist in this series. Maybe dev_cookie is
> appended to the end of the structure and indicated with a flag when it
> has some meaning.
sorry, I should have deleted it. ☹
>
> > + *
> > + * User is not allowed to access the device before the binding operation
> > + * is completed.
>
> s/not allowed to access/restricted from accessing/
got it.
>
> > + *
> > + * Unbind is automatically conducted when device fd is closed.
> > + *
> > + * @argsz: user filled size of this data.
> > + * @flags: reserved for future extension.
> > + * @dev_cookie: a per device cookie provided by userspace.
> > + * @iommufd: iommufd to bind. a negative value means noiommu.
>
> "Use a negative value for no-iommu, where supported", or better, should
> we define this explicitly as -1, or why not use a flag bit to specify
> no-iommu? Maybe minsz is only through flags for the noiommu use case.
> Thanks,
I don’t have preference here. maybe using -1 can save a flag bit for future
extension.
>
> > + * @out_devid: the device id generated by this bind. This field is valid
> > + * as long as the input @iommufd is valid. Otherwise, it is
> > + * meaningless.
> > + *
> > + * Return: 0 on success, -errno on failure.
> > + */
> > +struct vfio_device_bind_iommufd {
> > + __u32 argsz;
> > + __u32 flags;
> > + __aligned_u64 dev_cookie;
> > + __s32 iommufd;
> > + __u32 out_devid;
> > +};
> > +
> > +#define VFIO_DEVICE_BIND_IOMMUFD _IO(VFIO_TYPE, VFIO_BASE + 19)
> > +
> > /**
> > * VFIO_DEVICE_GET_INFO - _IOR(VFIO_TYPE, VFIO_BASE + 7,
> > * struct vfio_device_info)
Regards,
Yi Liu
