Re: [Qemu-devel] [PATCH] virtio: introduce grab/release_ioeventfd to fix vhost

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/11/2016 22:11, Alex Williamson wrote:
> On Fri, 11 Nov 2016 20:46:53 +0000
> Felipe Franciosi <felipe@nutanix.com> wrote:
> 
>> The trace you showed is exactly the same I encountered on vhost-scsi. And the one my (hacky) patched fixed. The summary of my investigation is on the patch description. I'm OOO so apologies for not being of more help. F.
> 
> Paolo's patch states that it overrides your patch, so I used Paolo's
> patch alone, but adding yours doesn't change anything, same assertion.
> Thanks,

Hmm it's late here and I could only reproduce with multiqueue.  Until I
reinstall the Windows VM with OVMF I'm grasping at straws, but these lines
should not be needed anymore now, so perhaps you can try this on top...

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 42467f1..c8a446e 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -247,7 +247,6 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign)
     }
 
     if (assign) {
-        assert(!bus->ioeventfd_started);
         r = event_notifier_init(notifier, 1);
         if (r < 0) {
             error_report("%s: unable to init event notifier: %s (%d)",
@@ -261,9 +260,6 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign)
         }
         return 0;
     } else {
-        if (!bus->ioeventfd_started) {
-            return 0;
-        }
         k->ioeventfd_assign(proxy, notifier, n, false);
     }
 

Michael, not yet s-o-b since I at least have to test vhost-scsi.

Paolo

> Alex
> 
>>> On 11 Nov 2016, at 20:38, Alex Williamson <alex.williamson@redhat.com> wrote:
>>>
>>> On Fri, 11 Nov 2016 20:28:55 +0100
>>> Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>   
>>>> Following the recent refactoring of virtio notifiers [1], more specifically
>>>> the patch ed08a2a0b ("virtio: use virtio_bus_set_host_notifier to
>>>> start/stop ioeventfd") that uses virtio_bus_set_host_notifier [2]
>>>> by default, core virtio code requires 'ioeventfd_started' to be set
>>>> to true/false when the host notifiers are configured.
>>>>
>>>> When vhost is stopped and started, however, there is a stop followed by
>>>> another start. Since ioeventfd_started was never set to true, the 'stop'
>>>> operation triggered by virtio_bus_set_host_notifier() will not result
>>>> in a call to virtio_pci_ioeventfd_assign(assign=false). This leaves
>>>> the memory regions with stale notifiers and results on the next start
>>>> triggering the following assertion:
>>>>
>>>>  kvm_mem_ioeventfd_add: error adding ioeventfd: File exists
>>>>  Aborted
>>>>
>>>> This patch reintroduces (hopefully in a cleaner way) the concept
>>>> that was present with ioeventfd_disabled before the refactoring.
>>>> When ioeventfd_grabbed>0, ioeventfd_started tracks whether ioeventfd
>>>> should be enabled or not, but ioeventfd is actually not started at
>>>> all until vhost releases the host notifiers.
>>>>
>>>> [1] http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg07748.html
>>>> [2] http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg07760.html
>>>>
>>>> Reported-by: Felipe Franciosi <felipe@nutanix.com>
>>>> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>> Reported-by: Alex Williamson <alex.williamson@redhat.com>
>>>> Fixes: ed08a2a0b ("virtio: use virtio_bus_set_host_notifier to start/stop ioeventfd")
>>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>>> ---
>>>>    You know you really screwed up when you get three Reported-bys...
>>>>    The patch is largish, but I've added lots of comments.
>>>>    It overrides Felipe's patch which did not for example fix vhost
>>>>    multiqueue (tests/vhost-user-test).
>>>>
>>>> hw/virtio/vhost.c              | 11 ++++------
>>>> hw/virtio/virtio-bus.c         | 50 ++++++++++++++++++++++++++++++++++++------
>>>> hw/virtio/virtio.c             | 16 ++++++++++++++
>>>> include/hw/virtio/virtio-bus.h | 14 ++++++++++++
>>>> include/hw/virtio/virtio.h     |  2 ++
>>>> 5 files changed, 79 insertions(+), 14 deletions(-)  
>>>
>>> I'm not entirely sure what to apply this to, it has conflicts with
>>> MST's last pull request, so I applied it to mainline, which for me was:
>>>
>>> 6bbcb76 MAINTAINERS: Remove obsolete stable branches
>>>
>>> But this just gives me a different failure, QEMU reports:
>>>
>>> kvm_mem_ioeventfd_add: error adding ioeventfd: File exists
>>>
>>> gdb backtrace:
>>>
>>> Thread 4 "CPU 1/KVM" received signal SIGABRT, Aborted.
>>> [Switching to Thread 0x7f60e4ce9700 (LWP 12239)]
>>> 0x00007f60f582b765 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
>>> 54      return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
>>> (gdb) bt
>>> #0  0x00007f60f582b765 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
>>> #1  0x00007f60f582d36a in __GI_abort () at abort.c:89
>>> #2  0x000055af0a40a8f0 in kvm_mem_ioeventfd_add (listener=0x55af0b4d6e70, section=0x7f60e4ce5ef0, match_data=false, data=0, e=0x55af0c2e3690)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/kvm-all.c:898
>>> #3  0x000055af0a4111d6 in address_space_add_del_ioeventfds (as=0x55af0aedef00 <address_space_memory>, fds_new=0x7f60d8000c00, fds_new_nb=9, fds_old=0x7f60d4319e80, fds_old_nb=8)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/memory.c:757
>>> #4  0x000055af0a4114e4 in address_space_update_ioeventfds (as=0x55af0aedef00 <address_space_memory>) at /net/gimli/home/alwillia/Work/qemu.git/memory.c:803
>>> #5  0x000055af0a411d1c in memory_region_transaction_commit () at /net/gimli/home/alwillia/Work/qemu.git/memory.c:932
>>> #6  0x000055af0a414881 in memory_region_add_eventfd (mr=0x55af0bbcf740, addr=0, size=0, match_data=false, data=0, e=0x55af0c2e3690) at /net/gimli/home/alwillia/Work/qemu.git/memory.c:1984
>>> #7  0x000055af0a71b0a8 in virtio_pci_ioeventfd_assign (d=0x55af0bbcea20, notifier=0x55af0c2e3690, n=0, assign=true) at hw/virtio/virtio-pci.c:300
>>> #8  0x000055af0a7216f1 in virtio_bus_set_host_notifier (bus=0x55af0bbd6db8, n=0, assign=true) at hw/virtio/virtio-bus.c:257
>>> #9  0x000055af0a48180b in vhost_dev_enable_notifiers (hdev=0x55af0b4d4f10, vdev=0x55af0bbd6e30) at /net/gimli/home/alwillia/Work/qemu.git/hw/virtio/vhost.c:1198
>>> #10 0x000055af0a457941 in vhost_net_start_one (net=0x55af0b4d4f10, dev=0x55af0bbd6e30) at /net/gimli/home/alwillia/Work/qemu.git/hw/net/vhost_net.c:227
>>> #11 0x000055af0a457e2d in vhost_net_start (dev=0x55af0bbd6e30, ncs=0x55af0c7e1890, total_queues=1) at /net/gimli/home/alwillia/Work/qemu.git/hw/net/vhost_net.c:324
>>> #12 0x000055af0a4523f2 in virtio_net_vhost_status (n=0x55af0bbd6e30, status=7 '\a') at /net/gimli/home/alwillia/Work/qemu.git/hw/net/virtio-net.c:156
>>> #13 0x000055af0a45268e in virtio_net_set_status (vdev=0x55af0bbd6e30, status=7 '\a') at /net/gimli/home/alwillia/Work/qemu.git/hw/net/virtio-net.c:229
>>> #14 0x000055af0a478874 in virtio_set_status (vdev=0x55af0bbd6e30, val=7 '\a') at /net/gimli/home/alwillia/Work/qemu.git/hw/virtio/virtio.c:898
>>> #15 0x000055af0a71b3c0 in virtio_ioport_write (opaque=0x55af0bbcea20, addr=18, val=7) at hw/virtio/virtio-pci.c:383
>>> #16 0x000055af0a71b824 in virtio_pci_config_write (opaque=0x55af0bbcea20, addr=18, val=7, size=1) at hw/virtio/virtio-pci.c:508
>>> #17 0x000055af0a4102fd in memory_region_write_accessor (mr=0x55af0bbcf310, addr=18, value=0x7f60e4ce64b8, size=1, shift=0, mask=255, attrs=...)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/memory.c:526
>>> #18 0x000055af0a410515 in access_with_adjusted_size (addr=18, value=0x7f60e4ce64b8, size=1, access_size_min=1, access_size_max=4, access=
>>>    0x55af0a410213 <memory_region_write_accessor>, mr=0x55af0bbcf310, attrs=...) at /net/gimli/home/alwillia/Work/qemu.git/memory.c:592
>>> #19 0x000055af0a412c55 in memory_region_dispatch_write (mr=0x55af0bbcf310, addr=18, data=7, size=1, attrs=...) at /net/gimli/home/alwillia/Work/qemu.git/memory.c:1323
>>> #20 0x000055af0a3be583 in address_space_write_continue (as=0x55af0aedede0 <address_space_io>, addr=49458, attrs=..., buf=0x7f6110aa0000 "\a", len=1, addr1=18, l=1, mr=0x55af0bbcf310)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/exec.c:2621
>>> #21 0x000055af0a3be6cb in address_space_write (as=0x55af0aedede0 <address_space_io>, addr=49458, attrs=..., buf=0x7f6110aa0000 "\a", len=1)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/exec.c:2666
>>> #22 0x000055af0a3bea57 in address_space_rw (as=0x55af0aedede0 <address_space_io>, addr=49458, attrs=..., buf=0x7f6110aa0000 "\a", len=1, is_write=true)
>>>    at /net/gimli/home/alwillia/Work/qemu.git/exec.c:2768
>>> #23 0x000055af0a40c8d7 in kvm_handle_io (port=49458, attrs=..., data=0x7f6110aa0000, direction=1, size=1, count=1) at /net/gimli/home/alwillia/Work/qemu.git/kvm-all.c:1800
>>> #24 0x000055af0a40cddd in kvm_cpu_exec (cpu=0x55af0b9c33f0) at /net/gimli/home/alwillia/Work/qemu.git/kvm-all.c:1958
>>> #25 0x000055af0a3f3c58 in qemu_kvm_cpu_thread_fn (arg=0x55af0b9c33f0) at /net/gimli/home/alwillia/Work/qemu.git/cpus.c:998
>>> #26 0x00007f60f5bc05ca in start_thread (arg=0x7f60e4ce9700) at pthread_create.c:333
>>> #27 0x00007f60f58fa0ed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>
>>> If I'm applying it to the wrong place, let me know.  Thanks,
>>>
>>> Alex
>>>   
>>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>>>> index 131f164..a8b5ab8 100644
>>>> --- a/hw/virtio/vhost.c
>>>> +++ b/hw/virtio/vhost.c
>>>> @@ -1186,17 +1186,14 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
>>>> int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
>>>> {
>>>>     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
>>>> -    VirtioBusState *vbus = VIRTIO_BUS(qbus);
>>>> -    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
>>>>     int i, r, e;
>>>>
>>>> -    if (!k->ioeventfd_assign) {
>>>> +    r = virtio_device_grab_ioeventfd(vdev);
>>>> +    if (r < 0) {
>>>>         error_report("binding does not support host notifiers");
>>>> -        r = -ENOSYS;
>>>>         goto fail;
>>>>     }
>>>>
>>>> -    virtio_device_stop_ioeventfd(vdev);
>>>>     for (i = 0; i < hdev->nvqs; ++i) {
>>>>         r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i,
>>>>                                          true);
>>>> @@ -1216,7 +1213,7 @@ fail_vq:
>>>>         }
>>>>         assert (e >= 0);
>>>>     }
>>>> -    virtio_device_start_ioeventfd(vdev);
>>>> +    virtio_device_release_ioeventfd(vdev);
>>>> fail:
>>>>     return r;
>>>> }
>>>> @@ -1239,7 +1236,7 @@ void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
>>>>         }
>>>>         assert (r >= 0);
>>>>     }
>>>> -    virtio_device_start_ioeventfd(vdev);
>>>> +    virtio_device_release_ioeventfd(vdev);
>>>> }
>>>>
>>>> /* Test and clear event pending status.
>>>> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
>>>> index bf61f66..42467f1 100644
>>>> --- a/hw/virtio/virtio-bus.c
>>>> +++ b/hw/virtio/virtio-bus.c
>>>> @@ -147,6 +147,38 @@ void virtio_bus_set_vdev_config(VirtioBusState *bus, uint8_t *config)
>>>>     }
>>>> }
>>>>
>>>> +int virtio_bus_grab_ioeventfd(VirtioBusState *bus)
>>>> +{
>>>> +    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
>>>> +
>>>> +    /* vhost can be used even if ioeventfd=off in the proxy device,
>>>> +     * so do not check k->ioeventfd_enabled.
>>>> +     */
>>>> +    if (!k->ioeventfd_assign) {
>>>> +        return -ENOSYS;
>>>> +    }
>>>> +
>>>> +    if (bus->ioeventfd_grabbed == 0 && bus->ioeventfd_started) {
>>>> +        virtio_bus_stop_ioeventfd(bus);
>>>> +        /* Remember that we need to restart ioeventfd
>>>> +         * when ioeventfd_grabbed becomes zero.
>>>> +         */
>>>> +        bus->ioeventfd_started = true;
>>>> +    }
>>>> +    bus->ioeventfd_grabbed++;
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +void virtio_bus_release_ioeventfd(VirtioBusState *bus)
>>>> +{
>>>> +    assert(bus->ioeventfd_grabbed != 0);
>>>> +    if (--bus->ioeventfd_grabbed == 0 && bus->ioeventfd_started) {
>>>> +        /* Force virtio_bus_start_ioeventfd to act.  */
>>>> +        bus->ioeventfd_started = false;
>>>> +        virtio_bus_start_ioeventfd(bus);
>>>> +    }
>>>> +}
>>>> +
>>>> int virtio_bus_start_ioeventfd(VirtioBusState *bus)
>>>> {
>>>>     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
>>>> @@ -161,10 +193,12 @@ int virtio_bus_start_ioeventfd(VirtioBusState *bus)
>>>>     if (bus->ioeventfd_started) {
>>>>         return 0;
>>>>     }
>>>> -    r = vdc->start_ioeventfd(vdev);
>>>> -    if (r < 0) {
>>>> -        error_report("%s: failed. Fallback to userspace (slower).", __func__);
>>>> -        return r;
>>>> +    if (!bus->ioeventfd_grabbed) {
>>>> +        r = vdc->start_ioeventfd(vdev);
>>>> +        if (r < 0) {
>>>> +            error_report("%s: failed. Fallback to userspace (slower).", __func__);
>>>> +            return r;
>>>> +        }
>>>>     }
>>>>     bus->ioeventfd_started = true;
>>>>     return 0;
>>>> @@ -179,9 +213,11 @@ void virtio_bus_stop_ioeventfd(VirtioBusState *bus)
>>>>         return;
>>>>     }
>>>>
>>>> -    vdev = virtio_bus_get_device(bus);
>>>> -    vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
>>>> -    vdc->stop_ioeventfd(vdev);
>>>> +    if (!bus->ioeventfd_grabbed) {
>>>> +        vdev = virtio_bus_get_device(bus);
>>>> +        vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
>>>> +        vdc->stop_ioeventfd(vdev);
>>>> +    }
>>>>     bus->ioeventfd_started = false;
>>>> }
>>>>
>>>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>>>> index bcbcfe0..89b0b80 100644
>>>> --- a/hw/virtio/virtio.c
>>>> +++ b/hw/virtio/virtio.c
>>>> @@ -2202,6 +2202,22 @@ void virtio_device_stop_ioeventfd(VirtIODevice *vdev)
>>>>     virtio_bus_stop_ioeventfd(vbus);
>>>> }
>>>>
>>>> +int virtio_device_grab_ioeventfd(VirtIODevice *vdev)
>>>> +{
>>>> +    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
>>>> +    VirtioBusState *vbus = VIRTIO_BUS(qbus);
>>>> +
>>>> +    return virtio_bus_grab_ioeventfd(vbus);
>>>> +}
>>>> +
>>>> +void virtio_device_release_ioeventfd(VirtIODevice *vdev)
>>>> +{
>>>> +    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
>>>> +    VirtioBusState *vbus = VIRTIO_BUS(qbus);
>>>> +
>>>> +    virtio_bus_release_ioeventfd(vbus);
>>>> +}
>>>> +
>>>> static void virtio_device_class_init(ObjectClass *klass, void *data)
>>>> {
>>>>     /* Set the default value here. */
>>>> diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
>>>> index fdf7fda..8a51e2c 100644
>>>> --- a/include/hw/virtio/virtio-bus.h
>>>> +++ b/include/hw/virtio/virtio-bus.h
>>>> @@ -97,6 +97,16 @@ struct VirtioBusState {
>>>>      * Set if ioeventfd has been started.
>>>>      */
>>>>     bool ioeventfd_started;
>>>> +
>>>> +    /*
>>>> +     * Set if ioeventfd has been grabbed by vhost.  When ioeventfd
>>>> +     * is grabbed by vhost, we track its started/stopped state (which
>>>> +     * depends in turn on the virtio status register), but do not
>>>> +     * register a handler for the ioeventfd.  When ioeventfd is
>>>> +     * released, if ioeventfd_started is true we finally register
>>>> +     * the handler so that QEMU's device model can use ioeventfd.
>>>> +     */
>>>> +    int ioeventfd_grabbed;
>>>> };
>>>>
>>>> void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp);
>>>> @@ -131,6 +141,10 @@ bool virtio_bus_ioeventfd_enabled(VirtioBusState *bus);
>>>> int virtio_bus_start_ioeventfd(VirtioBusState *bus);
>>>> /* Stop the ioeventfd. */
>>>> void virtio_bus_stop_ioeventfd(VirtioBusState *bus);
>>>> +/* Tell the bus that vhost is grabbing the ioeventfd. */
>>>> +int virtio_bus_grab_ioeventfd(VirtioBusState *bus);
>>>> +/* bus that vhost is not using the ioeventfd anymore. */
>>>> +void virtio_bus_release_ioeventfd(VirtioBusState *bus);
>>>> /* Switch from/to the generic ioeventfd handler */
>>>> int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign);
>>>>
>>>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>>>> index ac65d6a..35ede30 100644
>>>> --- a/include/hw/virtio/virtio.h
>>>> +++ b/include/hw/virtio/virtio.h
>>>> @@ -270,6 +270,8 @@ void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
>>>>                                                 bool with_irqfd);
>>>> int virtio_device_start_ioeventfd(VirtIODevice *vdev);
>>>> void virtio_device_stop_ioeventfd(VirtIODevice *vdev);
>>>> +int virtio_device_grab_ioeventfd(VirtIODevice *vdev);
>>>> +void virtio_device_release_ioeventfd(VirtIODevice *vdev);
>>>> bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev);
>>>> EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
>>>> void virtio_queue_host_notifier_read(EventNotifier *n);  
>>>   
> 
> 
>