From: Eugenio Perez Martin <eperezma@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: kvm list <kvm@vger.kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@gmail.com>,
Jason Wang <jasowang@redhat.com>,
qemu-level <qemu-devel@nongnu.org>,
Daniel Daly <dandaly0@gmail.com>,
virtualization@lists.linux-foundation.org,
Liran Alon <liralon@gmail.com>, Eli Cohen <eli@mellanox.com>,
Nitin Shrivastav <nitin.shrivastav@broadcom.com>,
Alex Barba <alex.barba@broadcom.com>,
Christophe Fontaine <cfontain@redhat.com>,
Juan Quintela <quintela@redhat.com>,
Lee Ballard <ballle98@gmail.com>,
Lars Ganrot <lars.ganrot@gmail.com>,
Rob Miller <rob.miller@broadcom.com>,
Stefano Garzarella <sgarzare@redhat.com>,
Howard Cai <howard.cai@gmail.com>,
Parav Pandit <parav@mellanox.com>, vm <vmireyno@marvell.com>,
Salil Mehta <mehta.salil.lnk@gmail.com>,
Stephen Finucane <stephenfin@redhat.com>,
Xiao W Wang <xiao.w.wang@intel.com>,
Sean Mooney <smooney@redhat.com>,
Jim Harford <jim.harford@broadcom.com>,
Dmytro Kazantsev <dmytro.kazantsev@gmail.com>,
Siwei Liu <loseweigh@gmail.com>,
Harpreet Singh Anand <hanand@xilinx.com>,
Michael Lilja <ml@napatech.com>, Max Gurtovoy <maxgu14@gmail.com>
Subject: Re: [RFC PATCH 07/27] vhost: Route guest->host notification through qemu
Date: Thu, 21 Jan 2021 21:10:38 +0100 [thread overview]
Message-ID: <CAJaqyWcN2LWC+XmU6zSG-kgrfhGc4VXjG+zj2LgCe3haLfeRgg@mail.gmail.com> (raw)
In-Reply-To: <20201210115052.GG416119@stefanha-x1.localdomain>
On Thu, Dec 10, 2020 at 12:51 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> On Wed, Dec 09, 2020 at 06:08:14PM +0100, Eugenio Perez Martin wrote:
> > On Mon, Dec 7, 2020 at 6:42 PM Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > > On Fri, Nov 20, 2020 at 07:50:45PM +0100, Eugenio Pérez wrote:
> > > > +{
> > > > + struct vhost_vring_file file = {
> > > > + .index = idx
> > > > + };
> > > > + VirtQueue *vq = virtio_get_queue(dev->vdev, idx);
> > > > + VhostShadowVirtqueue *svq;
> > > > + int r;
> > > > +
> > > > + svq = g_new0(VhostShadowVirtqueue, 1);
> > > > + svq->vq = vq;
> > > > +
> > > > + r = event_notifier_init(&svq->hdev_notifier, 0);
> > > > + assert(r == 0);
> > > > +
> > > > + file.fd = event_notifier_get_fd(&svq->hdev_notifier);
> > > > + r = dev->vhost_ops->vhost_set_vring_kick(dev, &file);
> > > > + assert(r == 0);
> > > > +
> > > > + return svq;
> > > > +}
> > >
> > > I guess there are assumptions about the status of the device? Does the
> > > virtqueue need to be disabled when this function is called?
> > >
> >
> > Yes. Maybe an assertion checking the notification state?
>
> Sounds good.
>
> > > > +
> > > > +static int vhost_sw_live_migration_stop(struct vhost_dev *dev)
> > > > +{
> > > > + int idx;
> > > > +
> > > > + vhost_dev_enable_notifiers(dev, dev->vdev);
> > > > + for (idx = 0; idx < dev->nvqs; ++idx) {
> > > > + vhost_sw_lm_shadow_vq_free(dev->sw_lm_shadow_vq[idx]);
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int vhost_sw_live_migration_start(struct vhost_dev *dev)
> > > > +{
> > > > + int idx;
> > > > +
> > > > + for (idx = 0; idx < dev->nvqs; ++idx) {
> > > > + dev->sw_lm_shadow_vq[idx] = vhost_sw_lm_shadow_vq(dev, idx);
> > > > + }
> > > > +
> > > > + vhost_dev_disable_notifiers(dev, dev->vdev);
> > >
> > > There is a race condition if the guest kicks the vq while this is
> > > happening. The shadow vq hdev_notifier needs to be set so the vhost
> > > device checks the virtqueue for requests that slipped in during the
> > > race window.
> > >
> >
> > I'm not sure if I follow you. If I understand correctly,
> > vhost_dev_disable_notifiers calls virtio_bus_cleanup_host_notifier,
> > and the latter calls virtio_queue_host_notifier_read. That's why the
> > documentation says "This might actually run the qemu handlers right
> > away, so virtio in qemu must be completely setup when this is
> > called.". Am I missing something?
>
> There are at least two cases:
>
> 1. Virtqueue kicks that come before vhost_dev_disable_notifiers().
> vhost_dev_disable_notifiers() notices that and calls
> virtio_queue_notify_vq(). Will handle_sw_lm_vq() be invoked or is the
> device's vq handler function invoked?
>
As I understand both the code and your question, no kick can call
handle_sw_lm_vq before vhost_dev_disable_notifiers (in particular,
before memory_region_add_eventfd calls in
virtio_{pci,mmio,ccw}_ioeventfd_assign(true) calls. So these will be
handled by the device.
> 2. Virtqueue kicks that come in after vhost_dev_disable_notifiers()
> returns. We hold the QEMU global mutex so the vCPU thread cannot
> perform MMIO/PIO dispatch immediately. The vCPU thread's
> ioctl(KVM_RUN) has already returned and will dispatch dispatch the
> MMIO/PIO access inside QEMU as soon as the global mutex is released.
> In other words, we're not taking the kvm.ko ioeventfd path but
> memory_region_dispatch_write_eventfds() should signal the ioeventfd
> that is registered at the time the dispatch occurs. Is that eventfd
> handled by handle_sw_lm_vq()?
>
I didn't think on that case, but it's being very difficult for me to
reproduce that behavior. It should be handled by handle_sw_lm_vq, but
maybe I'm trusting too much in vhost_dev_disable_notifiers.
> Neither of these cases are obvious from the code. At least comments
> would help but I suspect restructuring the code so the critical
> ioeventfd state changes happen in a sequence would make it even clearer.
Could you expand on this? That change is managed entirely by
virtio_bus_set_host_notifier, and the virtqueue callback is already
changed before the call to vhost_dev_disable_notifiers(). Did you mean
to restructure virtio_bus_set_host_notifier or
vhost_dev_disable_notifiers maybe?
Thanks!
next prev parent reply other threads:[~2021-01-21 20:13 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-20 18:50 [RFC PATCH 00/27] vDPA software assisted live migration Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 01/27] vhost: Add vhost_dev_can_log Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 02/27] vhost: Add device callback in vhost_migration_log Eugenio Pérez
2020-12-07 16:19 ` Stefan Hajnoczi
2020-12-09 12:20 ` Eugenio Perez Martin
2020-11-20 18:50 ` [RFC PATCH 03/27] vhost: Move log resize/put to vhost_dev_set_log Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 04/27] vhost: add vhost_kernel_set_vring_enable Eugenio Pérez
2020-12-07 16:43 ` Stefan Hajnoczi
2020-12-09 12:00 ` Eugenio Perez Martin
2020-12-09 16:08 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 05/27] vhost: Add hdev->dev.sw_lm_vq_handler Eugenio Pérez
2020-12-07 16:52 ` Stefan Hajnoczi
2020-12-09 15:02 ` Eugenio Perez Martin
2020-12-10 11:30 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 06/27] virtio: Add virtio_queue_get_used_notify_split Eugenio Pérez
2020-12-07 16:58 ` Stefan Hajnoczi
2021-01-12 18:21 ` Eugenio Perez Martin
2021-03-02 11:22 ` Stefan Hajnoczi
2021-03-02 18:34 ` Eugenio Perez Martin
2021-03-08 10:46 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 07/27] vhost: Route guest->host notification through qemu Eugenio Pérez
2020-12-07 17:42 ` Stefan Hajnoczi
2020-12-09 17:08 ` Eugenio Perez Martin
2020-12-10 11:50 ` Stefan Hajnoczi
2021-01-21 20:10 ` Eugenio Perez Martin [this message]
2020-11-20 18:50 ` [RFC PATCH 08/27] vhost: Add a flag for software assisted Live Migration Eugenio Pérez
2020-12-08 7:20 ` Stefan Hajnoczi
2020-12-09 17:57 ` Eugenio Perez Martin
2020-11-20 18:50 ` [RFC PATCH 09/27] vhost: Route host->guest notification through qemu Eugenio Pérez
2020-12-08 7:34 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 10/27] vhost: Allocate shadow vring Eugenio Pérez
2020-12-08 7:49 ` Stefan Hajnoczi
2020-12-08 8:17 ` Stefan Hajnoczi
2020-12-09 18:15 ` Eugenio Perez Martin
2020-11-20 18:50 ` [RFC PATCH 11/27] virtio: const-ify all virtio_tswap* functions Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 12/27] virtio: Add virtio_queue_full Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 13/27] vhost: Send buffers to device Eugenio Pérez
2020-12-08 8:16 ` Stefan Hajnoczi
2020-12-09 18:41 ` Eugenio Perez Martin
2020-12-10 11:55 ` Stefan Hajnoczi
2021-01-22 18:18 ` Eugenio Perez Martin
[not found] ` <CAJaqyWdNeaboGaSsXPA8r=mUsbctFLzACFKLX55yRQpTvjqxJw@mail.gmail.com>
2021-03-22 10:51 ` Stefan Hajnoczi
2021-03-22 15:55 ` Eugenio Perez Martin
2021-03-22 17:40 ` Stefan Hajnoczi
2021-03-24 19:04 ` Eugenio Perez Martin
2021-03-24 19:56 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 14/27] virtio: Remove virtio_queue_get_used_notify_split Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 15/27] vhost: Do not invalidate signalled used Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 16/27] virtio: Expose virtqueue_alloc_element Eugenio Pérez
2020-12-08 8:25 ` Stefan Hajnoczi
2020-12-09 18:46 ` Eugenio Perez Martin
2020-12-10 11:57 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 17/27] vhost: add vhost_vring_set_notification_rcu Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 18/27] vhost: add vhost_vring_poll_rcu Eugenio Pérez
2020-12-08 8:41 ` Stefan Hajnoczi
2020-12-09 18:48 ` Eugenio Perez Martin
2020-11-20 18:50 ` [RFC PATCH 19/27] vhost: add vhost_vring_get_buf_rcu Eugenio Pérez
2020-11-20 18:50 ` [RFC PATCH 20/27] vhost: Return used buffers Eugenio Pérez
2020-12-08 8:50 ` Stefan Hajnoczi
2020-11-20 18:50 ` [RFC PATCH 21/27] vhost: Add vhost_virtqueue_memory_unmap Eugenio Pérez
2020-11-20 18:51 ` [RFC PATCH 22/27] vhost: Add vhost_virtqueue_memory_map Eugenio Pérez
2020-11-20 18:51 ` [RFC PATCH 23/27] vhost: unmap qemu's shadow virtqueues on sw live migration Eugenio Pérez
2020-11-27 15:29 ` Stefano Garzarella
2020-11-30 7:54 ` Eugenio Perez Martin
2020-11-20 18:51 ` [RFC PATCH 24/27] vhost: iommu changes Eugenio Pérez
2020-12-08 9:02 ` Stefan Hajnoczi
2020-11-20 18:51 ` [RFC PATCH 25/27] vhost: Do not commit vhost used idx on vhost_virtqueue_stop Eugenio Pérez
2020-11-20 19:35 ` Eugenio Perez Martin
2020-11-20 18:51 ` [RFC PATCH 26/27] vhost: Add vhost_hdev_can_sw_lm Eugenio Pérez
2020-11-20 18:51 ` [RFC PATCH 27/27] vhost: forbid vhost devices logging Eugenio Pérez
2020-11-20 19:03 ` [RFC PATCH 00/27] vDPA software assisted live migration Eugenio Perez Martin
2020-11-20 19:30 ` no-reply
2020-11-25 7:08 ` Jason Wang
2020-11-25 12:03 ` Eugenio Perez Martin
2020-11-25 12:14 ` Eugenio Perez Martin
2020-11-26 3:07 ` Jason Wang
2020-11-27 15:44 ` Stefano Garzarella
2020-12-08 9:37 ` Stefan Hajnoczi
2020-12-09 9:26 ` Jason Wang
2020-12-09 15:57 ` Stefan Hajnoczi
2020-12-10 9:12 ` Jason Wang
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