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

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 10/4/22 1:36 PM, Christian Borntraeger wrote:
> 
> 
> 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)


Looks like this can be solved with EXPORT_SYMBOL_GPL(vfio_file_is_group);

Also:

arch/s390/kvm/../../../virt/kvm/vfio.c:64:28: warning: ‘kvm_vfio_file_iommu_group’ defined but not used [-Wunused-function]
   64 | static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~

kvm_vfio_file_iommu_group looks like it is now SPAPR-only

> 
> 
> Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> 
> At least the vfio-ap part

Nope, with this s390 vfio-pci at least breaks:

[  132.943389] kernel BUG at lib/list_debug.c:53!
[  132.943406] monitor event: 0040 ilc:2 [#1] SMP 
[  132.943410] Modules linked in: vfio_pci kvm vfio_pci_core irqbypass vfio_virqfd vhost_vsock vmw_vsock_virtio_transport_common vsock vhost vhost_iotlb nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defr
ag_ipv4 ip_set nf_tables nfnetlink sunrpc mlx5_ib ism smc ib_uverbs ib_core uvdevice s390_trng tape_3590 tape tape_class eadm_sch vfio_ccw mdev vfio_iommu_type1 vfio zcrypt_cex4 sch_fq_codel configfs ghash_s390 prng chacha_s390 libchacha mlx5_core aes_s390 des_s390 libdes sha3_512_s390 nvme sha3_256_s390 sha512_s390 sh
a256_s390 nvme_core sha1_s390 sha_common zfcp scsi_transport_fc pkey zcrypt rng_core autofs4 [last unloaded: vfio_pci]
[  132.943457] CPU: 12 PID: 4991 Comm: nose2 Tainted: G        W          6.0.0-rc4 #40
[  132.943460] Hardware name: IBM 3931 A01 782 (LPAR)
[  132.943462] Krnl PSW : 0704c00180000000 00000000cbc90568 (__list_del_entry_valid+0xd8/0xf0)
[  132.943469]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
[  132.943474] Krnl GPRS: 8000000000000001 0000000900000027 000000000000004e 00000000ccc1ffe0
[  132.943477]            00000000fffeffff 00000009fc290000 0000000000000000 0000000000000080
[  132.943480]            00000000acc86438 0000000000000000 00000000acc86420 00000000a1492800
[  132.943483]            00000000922a0000 000003ffb9dce260 00000000cbc90564 0000038004a6b9f8
[  132.943489] Krnl Code: 00000000cbc90558: c0200045eff3        larl    %r2,00000000cc54e53e
[  132.943489]            00000000cbc9055e: c0e50022c7d9        brasl   %r14,00000000cc0e9510
[  132.943489]           #00000000cbc90564: af000000            mc      0,0
[  132.943489]           >00000000cbc90568: b9040032            lgr     %r3,%r2
[  132.943489]            00000000cbc9056c: c0200045efd4        larl    %r2,00000000cc54e514
[  132.943489]            00000000cbc90572: c0e50022c7cf        brasl   %r14,00000000cc0e9510
[  132.943489]            00000000cbc90578: af000000            mc      0,0
[  132.943489]            00000000cbc9057c: 0707                bcr     0,%r7
[  132.943510] Call Trace:
[  132.943512]  [<00000000cbc90568>] __list_del_entry_valid+0xd8/0xf0 
[  132.943515] ([<00000000cbc90564>] __list_del_entry_valid+0xd4/0xf0)
[  132.943518]  [<000003ff8011a1b8>] vfio_group_detach_container+0x88/0x170 [vfio] 
[  132.943524]  [<000003ff801176c0>] vfio_device_remove_group.isra.0+0xb0/0x1e0 [vfio] 
[  132.943529]  [<000003ff804f9e54>] vfio_pci_core_unregister_device+0x34/0x80 [vfio_pci_core] 
[  132.943535]  [<000003ff804ae1c4>] vfio_pci_remove+0x2c/0x40 [vfio_pci] 
[  132.943539]  [<00000000cbd58c3c>] pci_device_remove+0x3c/0x98 
[  132.943542]  [<00000000cbdbdbce>] device_release_driver_internal+0x1c6/0x288 
[  132.943545]  [<00000000cbd4e284>] pci_stop_bus_device+0x94/0xc0 
[  132.943549]  [<00000000cbd4e570>] pci_stop_and_remove_bus_device_locked+0x30/0x48 
[  132.943552]  [<00000000cb55d980>] zpci_bus_remove_device+0x68/0xa8 
[  132.943555]  [<00000000cb556e82>] zpci_deconfigure_device+0x3a/0xe0 
[  132.943558]  [<00000000cbd65d04>] power_write_file+0x7c/0x130 
[  132.943561]  [<00000000cb8fbc90>] kernfs_fop_write_iter+0x138/0x210 
[  132.943565]  [<00000000cb837344>] vfs_write+0x194/0x2e0 "
[  132.943568]  [<00000000cb8376fa>] ksys_write+0x6a/0xf8 
[  132.943571]  [<00000000cc0f918c>] __do_syscall+0x1d4/0x200 
[  132.943575]  [<00000000cc107e42>] system_call+0x82/0xb0 
[  132.943577] Last Breaking-Event-Address:
[  132.943579]  [<00000000cc0e955c>] _printk+0x4c/0x58
[  132.943585] Kernel panic - not syncing: Fatal exception: panic_on_oops