Re: [PATCH v15 00/13] s390/vfio-ap: dynamic configuration support

[Tony Krowiak]

On 4/8/21 4:38 PM, Halil Pasic wrote:
> On Tue,  6 Apr 2021 11:31:09 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > Tony Krowiak (13):
> >    s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks
> The subsequent patches, re introduce this circular locking dependency
> problem. See my kernel messages for the details. The link we severe
> in the above patch is re-introduced at several places. One of them is
> assign_adapter_store().

Like in the patch referenced above, the lockdep splat occurs when
the APCB masks are set which requires acquisition of the kvm lock.
Patch 08/13, allow hot plug/unplug of AP resources using mdev,
introduces code that updates the APCB masks whenever an
adapter, domain or control domain is assigned or unassigned
as well as when a queue device is probed or removed.
I think the solution from the patch above can be implemented
here to resolve this problem.

> Regards,
> Halil
>
> [  +0.000236] vfio_ap matrix: MDEV: Registered
> [  +0.037919] vfio_mdev 4f77ad87-1e62-4959-8b7a-c677c98d2194: Adding to iommu group 1
> [  +0.000092] vfio_mdev 4f77ad87-1e62-4959-8b7a-c677c98d2194: MDEV: group_id = 1
>
> [Apr 8 22:31] ======================================================
> [  +0.000002] WARNING: possible circular locking dependency detected
> [  +0.000002] 5.12.0-rc6-00016-g5bea90816c56 #57 Not tainted
> [  +0.000002] ------------------------------------------------------
> [  +0.000002] CPU 1/KVM/6651 is trying to acquire lock:
> [  +0.000002] 00000000cef9d508 (&matrix_dev->lock){+.+.}-{3:3}, at: handle_pqap+0x56/0x1c8 [vfio_ap]
> [  +0.000011]
>                but task is already holding lock:
> [  +0.000001] 00000000d41f4308 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x90/0x898 [kvm]
> [  +0.000038]
>                which lock already depends on the new lock.
>
> [  +0.000002]
>                the existing dependency chain (in reverse order) is:
> [  +0.000001]
>                -> #2 (&vcpu->mutex){+.+.}-{3:3}:
> [  +0.000004]        validate_chain+0x796/0xa20
> [  +0.000006]        __lock_acquire+0x420/0x7c8
> [  +0.000003]        lock_acquire.part.0+0xec/0x1e8
> [  +0.000002]        lock_acquire+0xb8/0x208
> [  +0.000002]        __mutex_lock+0xa2/0x928
> [  +0.000005]        mutex_lock_nested+0x32/0x40
> [  +0.000002]        kvm_s390_cpus_to_pv+0x4e/0xf8 [kvm]
> [  +0.000019]        kvm_s390_handle_pv+0x1ce/0x6b0 [kvm]
> [  +0.000018]        kvm_arch_vm_ioctl+0x3ec/0x550 [kvm]
> [  +0.000019]        kvm_vm_ioctl+0x40e/0x4a8 [kvm]
> [  +0.000018]        __s390x_sys_ioctl+0xc0/0x100
> [  +0.000004]        do_syscall+0x7e/0xd0
> [  +0.000043]        __do_syscall+0xc0/0xd8
> [  +0.000004]        system_call+0x72/0x98
> [  +0.000004]
>                -> #1 (&kvm->lock){+.+.}-{3:3}:
> [  +0.000004]        validate_chain+0x796/0xa20
> [  +0.000002]        __lock_acquire+0x420/0x7c8
> [  +0.000002]        lock_acquire.part.0+0xec/0x1e8
> [  +0.000002]        lock_acquire+0xb8/0x208
> [  +0.000003]        __mutex_lock+0xa2/0x928
> [  +0.000002]        mutex_lock_nested+0x32/0x40
> [  +0.000002]        kvm_arch_crypto_set_masks+0x4a/0x2b8 [kvm]
> [  +0.000018]        vfio_ap_mdev_refresh_apcb+0xd0/0xe0 [vfio_ap]
> [  +0.000003]        assign_adapter_store+0x1f2/0x240 [vfio_ap]
> [  +0.000003]        kernfs_fop_write_iter+0x13e/0x1e0
> [  +0.000003]        new_sync_write+0x10a/0x198
> [  +0.000003]        vfs_write.part.0+0x196/0x290
> [  +0.000002]        ksys_write+0x6c/0xf8
> [  +0.000003]        do_syscall+0x7e/0xd0
> [  +0.000002]        __do_syscall+0xc0/0xd8
> [  +0.000003]        system_call+0x72/0x98
> [  +0.000002]
>                -> #0 (&matrix_dev->lock){+.+.}-{3:3}:
> [  +0.000004]        check_noncircular+0x16e/0x190
> [  +0.000002]        check_prev_add+0xec/0xf38
> [  +0.000002]        validate_chain+0x796/0xa20
> [  +0.000002]        __lock_acquire+0x420/0x7c8
> [  +0.000002]        lock_acquire.part.0+0xec/0x1e8
> [  +0.000002]        lock_acquire+0xb8/0x208
> [  +0.000002]        __mutex_lock+0xa2/0x928
> [  +0.000002]        mutex_lock_nested+0x32/0x40
> [  +0.000003]        handle_pqap+0x56/0x1c8 [vfio_ap]
> [  +0.000002]        handle_pqap+0xe2/0x1d8 [kvm]
> [  +0.000019]        kvm_handle_sie_intercept+0x134/0x248 [kvm]
> [  +0.000019]        vcpu_post_run+0x2b6/0x580 [kvm]
> [  +0.000018]        __vcpu_run+0x27e/0x388 [kvm]
> [  +0.000019]        kvm_arch_vcpu_ioctl_run+0x10a/0x278 [kvm]
> [  +0.000018]        kvm_vcpu_ioctl+0x2cc/0x898 [kvm]
> [  +0.000018]        __s390x_sys_ioctl+0xc0/0x100
> [  +0.000003]        do_syscall+0x7e/0xd0
> [  +0.000002]        __do_syscall+0xc0/0xd8
> [  +0.000002]        system_call+0x72/0x98
> [  +0.000003]
>                other info that might help us debug this:
>
> [  +0.000001] Chain exists of:
>                  &matrix_dev->lock --> &kvm->lock --> &vcpu->mutex
>
> [  +0.000005]  Possible unsafe locking scenario:
>
> [  +0.000001]        CPU0                    CPU1
> [  +0.000001]        ----                    ----
> [  +0.000002]   lock(&vcpu->mutex);
> [  +0.000002]                                lock(&kvm->lock);
> [  +0.000002]                                lock(&vcpu->mutex);
> [  +0.000002]   lock(&matrix_dev->lock);
> [  +0.000002]
>                 *** DEADLOCK ***
>
> [  +0.000002] 2 locks held by CPU 1/KVM/6651:
> [  +0.000002]  #0: 00000000d41f4308 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x90/0x898 [kvm]
> [  +0.000023]  #1: 00000000da2fc508 (&kvm->srcu){....}-{0:0}, at: __vcpu_run+0x1ec/0x388 [kvm]
> [  +0.000021]
>                stack backtrace:
> [  +0.000002] CPU: 6 PID: 6651 Comm: CPU 1/KVM Not tainted 5.12.0-rc6-00016-g5bea90816c56 #57
> [  +0.000004] Hardware name: IBM 8561 T01 701 (LPAR)
> [  +0.000001] Call Trace:
> [  +0.000002]  [<00000002010e7ef0>] show_stack+0x90/0xf8
> [  +0.000007]  [<00000002010fb5b2>] dump_stack+0xba/0x108
> [  +0.000002]  [<000000020053feb6>] check_noncircular+0x16e/0x190
> [  +0.000003]  [<0000000200541424>] check_prev_add+0xec/0xf38
> [  +0.000002]  [<0000000200542a06>] validate_chain+0x796/0xa20
> [  +0.000003]  [<0000000200545430>] __lock_acquire+0x420/0x7c8
> [  +0.000002]  [<00000002005441a4>] lock_acquire.part.0+0xec/0x1e8
> [  +0.000002]  [<0000000200544358>] lock_acquire+0xb8/0x208
> [  +0.000003]  [<000000020110aeea>] __mutex_lock+0xa2/0x928
> [  +0.000002]  [<000000020110b7a2>] mutex_lock_nested+0x32/0x40
> [  +0.000003]  [<000003ff8060fb5e>] handle_pqap+0x56/0x1c8 [vfio_ap]
> [  +0.000003]  [<000003ff80597412>] handle_pqap+0xe2/0x1d8 [kvm]
> [  +0.000018]  [<000003ff8058c924>] kvm_handle_sie_intercept+0x134/0x248 [kvm]
> [  +0.000020]  [<000003ff80588e96>] vcpu_post_run+0x2b6/0x580 [kvm]
> [  +0.000019]  [<000003ff805893de>] __vcpu_run+0x27e/0x388 [kvm]
> [  +0.000018]  [<000003ff80589d0a>] kvm_arch_vcpu_ioctl_run+0x10a/0x278 [kvm]
> [  +0.000019]  [<000003ff805704d4>] kvm_vcpu_ioctl+0x2cc/0x898 [kvm]
> [  +0.000019]  [<0000000200801ee8>] __s390x_sys_ioctl+0xc0/0x100
> [  +0.000003]  [<000000020046e7ae>] do_syscall+0x7e/0xd0
> [  +0.000003]  [<00000002010ffc20>] __do_syscall+0xc0/0xd8
> [  +0.000002]  [<0000000201110c42>] system_call+0x72/0x98
> [  +0.000003] INFO: lockdep is turned off.
> [  +6.846296] vfio_mdev 4f77ad87-1e62-4959-8b7a-c677c98d2194: Removing from iommu group 1
> [  +0.000028] vfio_mdev 4f77ad87-1e62-4959-8b7a-c677c98d2194: MDEV: detaching iommu
> [  +0.007677] vfio_ap matrix: MDEV: Unregistering
>
>
> >    s390/vfio-ap: use new AP bus interface to search for queue devices
> >    s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c
> >    s390/vfio-ap: manage link between queue struct and matrix mdev
> >    s390/vfio-ap: introduce shadow APCB
> >    s390/vfio-ap: refresh guest's APCB by filtering APQNs assigned to mdev
> >    s390/vfio-ap: allow assignment of unavailable AP queues to mdev device
> >    s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device
> >    s390/zcrypt: driver callback to indicate resource in use
> >    s390/vfio-ap: implement in-use callback for vfio_ap driver
> >    s390/vfio-ap: sysfs attribute to display the guest's matrix
> >    s390/zcrypt: notify drivers on config changed and scan complete
> >      callbacks
> >    s390/vfio-ap: update docs to include dynamic config support