> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, June 26, 2024 9:35 PM
>
> On Mon, Jun 17, 2024 at 05:53:32PM +0800, Yan Zhao wrote:
> > Reuse file f_inode as vfio device inode and associate pseudo path file
> > directly to inode allocated in vfio fs.
> >
> > Currently, vfio device is opened via 2 ways:
> > 1) via cdev open
> > vfio device is opened with a cdev device with file f_inode and address
> > space associated with a cdev inode;
> > 2) via VFIO_GROUP_GET_DEVICE_FD ioctl
> > vfio device is opened via a pseudo path file with file f_inode and
> > address space associated with an inode in anon_inode_fs.
> >
> > In commit b7c5e64fecfa ("vfio: Create vfio_fs_type with inode per device"),
> > an inode in vfio fs is allocated for each vfio device. However, this inode
> > in vfio fs is only used to assign its address space to that of a file
> > associated with another cdev inode or an inode in anon_inode_fs.
> >
> > This patch
> > - reuses cdev device inode as the vfio device inode when it's opened via
> > cdev way;
> > - allocates an inode in vfio fs, associate it to the pseudo path file,
> > and save it as the vfio device inode when the vfio device is opened via
> > VFIO_GROUP_GET_DEVICE_FD ioctl.
> >
> > File address space will then point automatically to the address space of
> > the vfio device inode. Tools like unmap_mapping_range() can then zap all
> > vmas associated with the vfio device.
> >
> > Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> > ---
> > drivers/vfio/device_cdev.c | 9 ++++---
> > drivers/vfio/group.c | 21 ++--------------
> > drivers/vfio/vfio.h | 2 ++
> > drivers/vfio/vfio_main.c | 49 +++++++++++++++++++++++++++-----------
> > 4 files changed, 43 insertions(+), 38 deletions(-)
> >
> > diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> > index bb1817bd4ff3..a4eec8e88f5c 100644
> > --- a/drivers/vfio/device_cdev.c
> > +++ b/drivers/vfio/device_cdev.c
> > @@ -40,12 +40,11 @@ int vfio_device_fops_cdev_open(struct inode
> *inode, struct file *filep)
> > filep->private_data = df;
> >
> > /*
> > - * Use the pseudo fs inode on the device to link all mmaps
> > - * to the same address space, allowing us to unmap all vmas
> > - * associated to this device using unmap_mapping_range().
> > + * mmaps are linked to the address space of the inode of device cdev.
> > + * Save the inode of device cdev in device->inode to allow
> > + * unmap_mapping_range() to unmap all vmas.
> > */
> > - filep->f_mapping = device->inode->i_mapping;
> > -
> > + device->inode = inode;
>
> This doesn't seem right.. There is only one device but multiple file
> can be opened on that device.
>
> We expect every open file to have a unique inode otherwise the
> unmap_mapping_range() will not function properly.
>
Does it mean that the existing code is already broken? there is only
one vfio-fs inode per device (allocated at vfio_init_device()).
And if we expect unique inode per open file then there will be a list
of inodes tracked under vfio_pci_core_device for unmap_mapping_range()
but it's also not the case today:
static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev)
{
struct vfio_device *core_vdev = &vdev->vdev;
loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
loff_t len = end - start;
unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true);
}
