On Fri, Jun 28, 2024 at 05:48:11PM +0800, Yi Liu wrote: > On 2024/6/28 13:21, Yan Zhao wrote: > > On Thu, Jun 27, 2024 at 09:42:09AM -0300, Jason Gunthorpe wrote: > > > On Thu, Jun 27, 2024 at 05:51:01PM +0800, Yan Zhao wrote: > > > > > > > > > > This doesn't seem right.. There is only one device but multiple file > > > > > > > can be opened on that device. > > > > Maybe we can put this assignment to vfio_df_ioctl_bind_iommufd() after > > > > vfio_df_open() makes sure device->open_count is 1. > > > > > > Yeah, that seems better. > > > > > > Logically it would be best if all places set the inode once the > > > inode/FD has been made to be the one and only way to access it. > > For group path, I'm afraid there's no such a place ensuring only one active fd > > in kernel. > > I tried modifying QEMU to allow two openings and two assignments of the same > > device. It works and appears to guest that there were 2 devices, though this > > ultimately leads to device malfunctions in guest. > > > > > > BTW, in group path, what's the benefit of allowing multiple open of device? > > > > > > I don't know, the thing that opened the first FD can just dup it, no > > > idea why two different FDs would be useful. It is something we removed > > > in the cdev flow > > > > > Thanks. However, from the code, it reads like a drawback of the cdev flow :) > > I don't understand why the group path is secure though. > > > > /* > > * Only the group path allows the device to be opened multiple > > * times. The device cdev path doesn't have a secure way for it. > > */ > > if (device->open_count != 0 && !df->group) > > return -EINVAL; > > > > > > The group path only allow single group open, so the device FDs retrieved > via the group is just within the opener of the group. This secure is built > on top of single open of group. What if the group is opened for only once but VFIO_GROUP_GET_DEVICE_FD ioctl is called for multiple times?
