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Subject: Re: [PATCH v3 0/8] vhost: Reset batched descriptors on SET_VRING_BASE
 call
From:   Christian Borntraeger <borntraeger@de.ibm.com>
To:     Eugenio Perez Martin <eperezma@redhat.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
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        <virtualization@lists.linux-foundation.org>,
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        Cornelia Huck <cohuck@redhat.com>
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Date:   Wed, 1 Apr 2020 21:13:23 +0200
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>> Would it be possible to investigate when qemu launches the offending ioctls?
> 
> During guest reboot. This is obvious, no?
> 


For example during reboot we do re-setup the virt queues:

#1  0x00000000010f3e7a in vhost_kernel_set_vring_base (dev=0x21f5f30, ring=0x3ff84d74e88) at /home/cborntra/REPOS/qemu/hw/virtio/vhost-backend.c:126
#2  0x00000000010f2f92 in vhost_virtqueue_start (idx=0, vq=0x21f6180, vdev=0x241d570, dev=0x21f5f30) at /home/cborntra/REPOS/qemu/hw/virtio/vhost.c:1016
#3  vhost_dev_start (hdev=hdev@entry=0x21f5f30, vdev=vdev@entry=0x241d570) at /home/cborntra/REPOS/qemu/hw/virtio/vhost.c:1646
#4  0x00000000011c265a in vhost_net_start_one (dev=0x241d570, net=0x21f5f30) at /home/cborntra/REPOS/qemu/hw/net/vhost_net.c:236
#5  vhost_net_start (dev=dev@entry=0x241d570, ncs=0x2450f40, total_queues=total_queues@entry=1) at /home/cborntra/REPOS/qemu/hw/net/vhost_net.c:338
#6  0x00000000010cfdfe in virtio_net_vhost_status (status=15 '\017', n=0x241d570) at /home/cborntra/REPOS/qemu/hw/net/virtio-net.c:250
#7  virtio_net_set_status (vdev=0x241d570, status=<optimized out>) at /home/cborntra/REPOS/qemu/hw/net/virtio-net.c:331
#8  0x00000000010eaef4 in virtio_set_status (vdev=vdev@entry=0x241d570, val=<optimized out>) at /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1956
#9  0x000000000110ba78 in virtio_ccw_cb (sch=0x2422c30, ccw=...) at /home/cborntra/REPOS/qemu/hw/s390x/virtio-ccw.c:509
#10 0x00000000011053fc in css_interpret_ccw (sch=sch@entry=0x2422c30, ccw_addr=<optimized out>, suspend_allowed=suspend_allowed@entry=false) at /home/cborntra/REPOS/qemu/hw/s390x/css.c:1108
#11 0x000000000110557c in sch_handle_start_func_virtual (sch=0x2422c30) at /home/cborntra/REPOS/qemu/hw/s390x/css.c:1162
#12 do_subchannel_work_virtual (sch=0x2422c30) at /home/cborntra/REPOS/qemu/hw/s390x/css.c:1256
#13 0x0000000001168592 in ioinst_handle_ssch (cpu=cpu@entry=0x234b920, reg1=<optimized out>, ipb=<optimized out>, ra=ra@entry=0) at /home/cborntra/REPOS/qemu/target/s390x/ioinst.c:218
#14 0x0000000001170012 in handle_b2 (ipa1=<optimized out>, run=0x3ff97880000, cpu=0x234b920) at /home/cborntra/REPOS/qemu/target/s390x/kvm.c:1279
#15 handle_instruction (run=0x3ff97880000, cpu=0x234b920) at /home/cborntra/REPOS/qemu/target/s390x/kvm.c:1664
#16 handle_intercept (cpu=0x234b920) at /home/cborntra/REPOS/qemu/target/s390x/kvm.c:1747
#17 kvm_arch_handle_exit (cs=cs@entry=0x234b920, run=run@entry=0x3ff97880000) at /home/cborntra/REPOS/qemu/target/s390x/kvm.c:1937
#18 0x00000000010972dc in kvm_cpu_exec (cpu=cpu@entry=0x234b920) at /home/cborntra/REPOS/qemu/accel/kvm/kvm-all.c:2445
#19 0x00000000010784f6 in qemu_kvm_cpu_thread_fn (arg=0x234b920) at /home/cborntra/REPOS/qemu/cpus.c:1246
#20 qemu_kvm_cpu_thread_fn (arg=arg@entry=0x234b920) at /home/cborntra/REPOS/qemu/cpus.c:1218
#21 0x00000000013891fa in qemu_thread_start (args=0x2372f30) at /home/cborntra/REPOS/qemu/util/qemu-thread-posix.c:519
#22 0x000003ff93809ed6 in start_thread () from target:/lib64/libpthread.so.0
#23 0x000003ff93705e46 in thread_start () from target:/lib64/libc.so.6