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

Liu, Yi L
2023-03-10T05:50:43Z

> From: Alexey Kardashevskiy <aik@amd.com>
> Sent: Friday, March 10, 2023 10:39 AM
>
> 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().
> > + */

device->open_count is sure to be non-zero if df->access_granted
is true. Otherwise, it means this device file has not opened device
successfully, so no need to do further tidy up.

> > + 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?

Thanks, I think this was fixed by the code I marked above. I think
it was raised in v2 review. Should have been fixed after that. Have
tried v5 or v6? If still have issue, please feel free let me know it.

https://lore.kernel.org/kvm/Y+HIWRM%2FTjWcuT6I@yzhao56-desk.sh.intel.com/

Regards,
Yi Liu