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

Christian Borntraeger
2022-10-04T15:45:11Z

Am 04.10.22 um 17:40 schrieb Jason Gunthorpe:
> On Tue, Oct 04, 2022 at 05:19:07PM +0200, Christian Borntraeger wrote:
>> Am 27.09.22 um 22:05 schrieb Alex Williamson:
>>> On Mon, 26 Sep 2022 13:03:56 -0400
>>> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
>>>
>>>> On 9/22/22 8:06 PM, Jason Gunthorpe wrote:
>>>>> The iommu_group comes from the struct device that a driver has been bound
>>>>> to and then created a struct vfio_device against. To keep the iommu layer
>>>>> sane we want to have a simple rule that only an attached driver should be
>>>>> using the iommu API. Particularly only an attached driver should hold
>>>>> ownership.
>>>>>
>>>>> In VFIO's case since it uses the group APIs and it shares between
>>>>> different drivers it is a bit more complicated, but the principle still
>>>>> holds.
>>>>>
>>>>> Solve this by waiting for all users of the vfio_group to stop before
>>>>> allowing vfio_unregister_group_dev() to complete. This is done with a new
>>>>> completion to know when the users go away and an additional refcount to
>>>>> keep track of how many device drivers are sharing the vfio group. The last
>>>>> driver to be unregistered will clean up the group.
>>>>>
>>>>> This solves crashes in the S390 iommu driver that come because VFIO ends
>>>>> up racing releasing ownership (which attaches the default iommu_domain to
>>>>> the device) with the removal of that same device from the iommu
>>>>> driver. This is a side case that iommu drivers should not have to cope
>>>>> with.
>>>>>
>>>>> iommu driver failed to attach the default/blocking domain
>>>>> WARNING: CPU: 0 PID: 5082 at drivers/iommu/iommu.c:1961 iommu_detach_group+0x6c/0x80
>>>>> Modules linked in: macvtap macvlan tap vfio_pci vfio_pci_core irqbypass vfio_virqfd kvm 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_defrag_ipv4 ip_set nf_tables nfnetlink mlx5_ib sunrpc ib_uverbs ism smc uvdevice ib_core s390_trng eadm_sch tape_3590 tape tape_class vfio_ccw mdev vfio_iommu_type1 vfio zcrypt_cex4 sch_fq_codel configfs ghash_s390 prng chacha_s390 libchacha aes_s390 mlx5_core des_s390 libdes sha3_512_s390 nvme sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common nvme_core zfcp scsi_transport_fc pkey zcrypt rng_core autofs4
>>>>> CPU: 0 PID: 5082 Comm: qemu-system-s39 Tainted: G W 6.0.0-rc3 #5
>>>>> Hardware name: IBM 3931 A01 782 (LPAR)
>>>>> Krnl PSW : 0704c00180000000 000000095bb10d28 (iommu_detach_group+0x70/0x80)
>>>>> 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
>>>>> Krnl GPRS: 0000000000000001 0000000900000027 0000000000000039 000000095c97ffe0
>>>>> 00000000fffeffff 00000009fc290000 00000000af1fda50 00000000af590b58
>>>>> 00000000af1fdaf0 0000000135c7a320 0000000135e52258 0000000135e52200
>>>>> 00000000a29e8000 00000000af590b40 000000095bb10d24 0000038004b13c98
>>>>> Krnl Code: 000000095bb10d18: c020003d56fc larl %r2,000000095c2bbb10
>>>>> 000000095bb10d1e: c0e50019d901 brasl %r14,000000095be4bf20
>>>>> #000000095bb10d24: af000000 mc 0,0
>>>>> >000000095bb10d28: b904002a lgr %r2,%r10
>>>>> 000000095bb10d2c: ebaff0a00004 lmg %r10,%r15,160(%r15)
>>>>> 000000095bb10d32: c0f4001aa867 brcl 15,000000095be65e00
>>>>> 000000095bb10d38: c004002168e0 brcl 0,000000095bf3def8
>>>>> 000000095bb10d3e: eb6ff0480024 stmg %r6,%r15,72(%r15)
>>>>> Call Trace:
>>>>> [<000000095bb10d28>] iommu_detach_group+0x70/0x80
>>>>> ([<000000095bb10d24>] iommu_detach_group+0x6c/0x80)
>>>>> [<000003ff80243b0e>] vfio_iommu_type1_detach_group+0x136/0x6c8 [vfio_iommu_type1]
>>>>> [<000003ff80137780>] __vfio_group_unset_container+0x58/0x158 [vfio]
>>>>> [<000003ff80138a16>] vfio_group_fops_unl_ioctl+0x1b6/0x210 [vfio]
>>>>> pci 0004:00:00.0: Removing from iommu group 4
>>>>> [<000000095b5b62e8>] __s390x_sys_ioctl+0xc0/0x100
>>>>> [<000000095be5d3b4>] __do_syscall+0x1d4/0x200
>>>>> [<000000095be6c072>] system_call+0x82/0xb0
>>>>> Last Breaking-Event-Address:
>>>>> [<000000095be4bf80>] __warn_printk+0x60/0x68
>>>>>
>>>>> It indicates that domain->ops->attach_dev() failed because the driver has
>>>>> already passed the point of destructing the device.
>>>>>
>>>>> Fixes: 9ac8545199a1 ("iommu: Fix use-after-free in iommu_release_device")
>>>>> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
>>>>> Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
>>>>> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>>>>> ---
>>>>> drivers/vfio/vfio.h | 8 +++++
>>>>> drivers/vfio/vfio_main.c | 68 ++++++++++++++++++++++++++--------------
>>>>> 2 files changed, 53 insertions(+), 23 deletions(-)
>>>>>
>>>>> v2
>>>>> - Rebase on the vfio struct device series and the container.c series
>>>>> - Drop patches 1 & 2, we need to have working error unwind, so another
>>>>> test is not a problem
>>>>> - Fold iommu_group_remove_device() into vfio_device_remove_group() so
>>>>> that it forms a strict pairing with the two allocation functions.
>>>>> - Drop the iommu patch from the series, it needs more work and discussion
>>>>> v1 https://lore.kernel.org/r/0-v1-ef00ffecea52+2cb-iommu_group_lifetime_jgg@nvidia.com
>>>>>
>>>>> This could probably use another quick sanity test due to all the rebasing,
>>>>> Alex if you are happy let's wait for Matthew.
>>>>
>>>> I have been re-running the same series of tests on this version (on top of vfio-next) and this still resolves the reported issue. Thanks Jason!
>>>
>>> Thanks all. Applied to vfio next branch for v6.1. Thanks,
>>
>> So now I have bisected this to a regression in our KVM CI for vfio-ap. Our testcase MultipleMdevAPMatrixTestCase hangs forever.
>> I see virtnodedevd spinning 100% and "mdevctl stop --uuid=d70d7685-a1b5-47a1-bdea-336925e0a95d" seems to wait for something:
>>
>> [ 186.815543] task:mdevctl state:D stack: 0 pid: 1639 ppid: 1604 flags:0x00000001
>> [ 186.815546] Call Trace:
>> [ 186.815547] [<0000002baf277386>] __schedule+0x296/0x650
>> [ 186.815549] [<0000002baf2777a2>] schedule+0x62/0x108
>> [ 186.815551] [<0000002baf27db20>] schedule_timeout+0xc0/0x108
>> [ 186.815553] [<0000002baf278166>] __wait_for_common+0xc6/0x250
>> [ 186.815556] [<000003ff800c263a>] vfio_device_remove_group.isra.0+0xb2/0x118 [vfio]
>> [ 186.815561] [<000003ff805caadc>] vfio_ap_mdev_remove+0x2c/0x198 [vfio_ap]
>> [ 186.815565] [<0000002baef1d4de>] device_release_driver_internal+0x1c6/0x288
>> [ 186.815570] [<0000002baef1b27c>] bus_remove_device+0x10c/0x198
>> [ 186.815572] [<0000002baef14b54>] device_del+0x19c/0x3e0
>> [ 186.815575] [<000003ff800d9e3a>] mdev_device_remove+0xb2/0x108 [mdev]
>> [ 186.815579] [<000003ff800da096>] remove_store+0x7e/0x90 [mdev]
>> [ 186.815581] [<0000002baea53c30>] kernfs_fop_write_iter+0x138/0x210
>> [ 186.815586] [<0000002bae98e310>] vfs_write+0x1a0/0x2f0
>> [ 186.815588] [<0000002bae98e6d8>] ksys_write+0x70/0x100
>> [ 186.815590] [<0000002baf26fe2c>] __do_syscall+0x1d4/0x200
>> [ 186.815593] [<0000002baf27eb42>] system_call+0x82/0xb0
>
> 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)'
65272 0 lr-x------. 1 root root 64 4. Okt 17:42 21 -> anon_inode:inotify
65273 0 lr-x------. 1 root root 64 4. Okt 17:42 23 -> 'pipe:[30158]'
65274 0 lr-x------. 1 root root 64 4. Okt 17:42 25 -> 'pipe:[30159]'
51481 0 lrwx------. 1 root root 64 4. Okt 17:16 3 -> 'socket:[43590]'
65255 0 lrwx------. 1 root root 64 4. Okt 17:42 4 -> 'socket:[43591]'
65256 0 lrwx------. 1 root root 64 4. Okt 17:42 5 -> 'socket:[30947]'
65257 0 lrwx------. 1 root root 64 4. Okt 17:42 6 -> 'socket:[51483]'
65258 0 l-wx------. 1 root root 64 4. Okt 17:42 7 -> /run/virtnodedevd.pid
65259 0 lr-x------. 1 root root 64 4. Okt 17:42 8 -> 'pipe:[51484]'
65260 0 l-wx------. 1 root root 64 4. Okt 17:42 9 -> 'pipe:[51484]'

/proc/mdevctl/fd
59494 0 dr-x------. 2 root root 0 4. Okt 17:16 .
59493 0 dr-xr-xr-x. 9 root root 0 4. Okt 17:16 ..
59495 0 lrwx------. 1 root root 64 4. Okt 17:16 0 -> /dev/null
59496 0 l-wx------. 1 root root 64 4. Okt 17:16 1 -> 'pipe:[30158]'
59497 0 l-wx------. 1 root root 64 4. Okt 17:16 2 -> 'pipe:[30159]'
59498 0 l-wx------. 1 root root 64 4. Okt 17:16 3 -> /sys/devices/vfio_ap/matrix/d70d7685-a1b5-47a1-bdea-336925e0a95d/remove