Re: [PATCH v2] vfio: Follow a strict lifetime for struct iommu_group

Christian Borntraeger
2022-10-04T17:48:59Z

Am 04.10.22 um 19:36 schrieb Christian Borntraeger:
>
>
> Am 04.10.22 um 18:28 schrieb Jason Gunthorpe:
>> On Tue, Oct 04, 2022 at 05:44:53PM +0200, Christian Borntraeger wrote:
>>
>>>> Does some userspace have the group FD open when it stucks like this,
>>>> eg what does fuser say?
>>>
>>> /proc/<virtnodedevd>/fd
>>> 51480 0 dr-x------. 2 root root  0  4. Okt 17:16 .
>>> 43593 0 dr-xr-xr-x. 9 root root  0  4. Okt 17:16 ..
>>> 65252 0 lr-x------. 1 root root 64  4. Okt 17:42 0 -> /dev/null
>>> 65253 0 lrwx------. 1 root root 64  4. Okt 17:42 1 -> 'socket:[51479]'
>>> 65261 0 lrwx------. 1 root root 64  4. Okt 17:42 10 -> 'anon_inode:[eventfd]'
>>> 65262 0 lrwx------. 1 root root 64  4. Okt 17:42 11 -> 'socket:[51485]'
>>> 65263 0 lrwx------. 1 root root 64  4. Okt 17:42 12 -> 'socket:[51487]'
>>> 65264 0 lrwx------. 1 root root 64  4. Okt 17:42 13 -> 'socket:[51486]'
>>> 65265 0 lrwx------. 1 root root 64  4. Okt 17:42 14 -> 'anon_inode:[eventfd]'
>>> 65266 0 lrwx------. 1 root root 64  4. Okt 17:42 15 -> 'socket:[60421]'
>>> 65267 0 lrwx------. 1 root root 64  4. Okt 17:42 16 -> 'anon_inode:[eventfd]'
>>> 65268 0 lrwx------. 1 root root 64  4. Okt 17:42 17 -> 'socket:[28008]'
>>> 65269 0 l-wx------. 1 root root 64  4. Okt 17:42 18 -> /run/libvirt/nodedev/driver.pid
>>> 65270 0 lrwx------. 1 root root 64  4. Okt 17:42 19 -> 'socket:[28818]'
>>> 65254 0 lrwx------. 1 root root 64  4. Okt 17:42 2 -> 'socket:[51479]'
>>> 65271 0 lr-x------. 1 root root 64  4. Okt 17:42 20 -> '/dev/vfio/3 (deleted)'
>>
>> Seems like a userspace bug to keep the group FD open after the /dev/
>> file has been deleted :|
>>
>> What do you think about this?
>>
>> commit a54a852b1484b1605917a8f4d80691db333b25ed
>> Author: Jason Gunthorpe <jgg@ziepe.ca>
>> Date:   Tue Oct 4 13:14:37 2022 -0300
>>
>>      vfio: Make the group FD disassociate from the iommu_group
>>      Allow the vfio_group struct to exist with a NULL iommu_group pointer. When
>>      the pointer is NULL the vfio_group users promise not to touch the
>>      iommu_group. This allows a driver to be hot unplugged while userspace is
>>      keeping the group FD open.
>>      SPAPR mode is excluded from this behavior because of how it wrongly hacks
>>      part of its iommu interface through KVM. Due to this we loose control over
>>      what it is doing and cannot revoke the iommu_group usage in the IOMMU
>>      layer via vfio_group_detach_container().
>>      Thus, for SPAPR the group FDs must still be closed before a device can be
>>      hot unplugged.
>>      This fixes a userspace regression where we learned that virtnodedevd
>>      leaves a group FD open even though the /dev/ node for it has been deleted
>>      and all the drivers for it unplugged.
>>      Fixes: ca5f21b25749 ("vfio: Follow a strict lifetime for struct iommu_group")
>>      Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>>      Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>
> Almost :-)
>
> drivers/vfio/vfio_main.c: In function 'vfio_file_is_group':
> drivers/vfio/vfio_main.c:1606:47: error: expected ')' before ';' token
>  1606 |         return (file->f_op == &vfio_group_fops;
>       |                ~                              ^
>       |                                               )
> drivers/vfio/vfio_main.c:1606:48: error: expected ';' before '}' token
>  1606 |         return (file->f_op == &vfio_group_fops;
>       |                                                ^
>       |                                                ;
>  1607 | }
>       | ~
>
>
> With that fixed I get:
>
> ERROR: modpost: "vfio_file_is_group" [drivers/vfio/pci/vfio-pci-core.ko] undefined!
>
> With that worked around (m -> y)
>
>
> Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>
> At least the vfio-ap part

Matthew, Eric, can you verify this on top of vfio-next with vfio-ccw and vfio pci?