Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
On Fri, Dec 23, 2022 at 3:39 PM Alvaro Karsz wrote: > > > This needs to be proposed to the virtio spec first. And actually we > > need more than this: > > > > 1) we still need a way to deal with the device without this feature > > 2) driver can't depend solely on what is advertised by the device (e.g > > device can choose to advertise a very long timeout) > > I think that I wasn't clear, sorry. > I'm not talking about a new virtio feature, I'm talking about a situation > when: > * virtio_net issues a control command. > * the device gets the command, but somehow, completes the command > after timeout. > * virtio_net assumes that the command failed (timeout), and issues a > different control command. > * virtio_net will then call virtqueue_wait_for_used, and will > immediately get the previous response (If I'm not wrong). > > So, this is not a new feature that I'm proposing, just a situation > that may occur due to cvq timeouts. > > Anyhow, your solution calling BAD_RING if we reach a timeout should > prevent this situation. Right, that is the goal. Thanks > > Thanks > ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
On Fri, Dec 23, 2022 at 4:05 PM Eugenio Perez Martin
wrote:
>
> On Fri, Dec 23, 2022 at 4:04 AM Jason Wang wrote:
> >
> > On Thu, Dec 22, 2022 at 5:19 PM Eugenio Perez Martin
> > wrote:
> > >
> > > On Thu, Dec 22, 2022 at 7:05 AM Jason Wang wrote:
> > > >
> > > > We used to busy waiting on the cvq command this tends to be
> > > > problematic since:
> > > >
> > > > 1) CPU could wait for ever on a buggy/malicous device
> > > > 2) There's no wait to terminate the process that triggers the cvq
> > > >command
> > > >
> > > > So this patch switch to use sleep with a timeout (1s) instead of busy
> > > > polling for the cvq command forever. This gives the scheduler a breath
> > > > and can let the process can respond to a signal.
> > > >
> > > > Signed-off-by: Jason Wang
> > > > ---
> > > > drivers/net/virtio_net.c | 15 ---
> > > > 1 file changed, 8 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 8225496ccb1e..69173049371f 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct
> > > > virtnet_info *vi)
> > > > vi->rx_mode_work_enabled = false;
> > > > spin_unlock_bh(&vi->rx_mode_lock);
> > > >
> > > > + virtqueue_wake_up(vi->cvq);
> > > > flush_work(&vi->rx_mode_work);
> > > > }
> > > >
> > > > @@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info
> > > > *vi, struct receive_queue *rq,
> > > > return !oom;
> > > > }
> > > >
> > > > +static void virtnet_cvq_done(struct virtqueue *cvq)
> > > > +{
> > > > + virtqueue_wake_up(cvq);
> > > > +}
> > > > +
> > > > static void skb_recv_done(struct virtqueue *rvq)
> > > > {
> > > > struct virtnet_info *vi = rvq->vdev->priv;
> > > > @@ -2024,12 +2030,7 @@ static bool virtnet_send_command(struct
> > > > virtnet_info *vi, u8 class, u8 cmd,
> > > > if (unlikely(!virtqueue_kick(vi->cvq)))
> > > > return vi->ctrl->status == VIRTIO_NET_OK;
> > > >
> > > > - /* Spin for a response, the kick causes an ioport write,
> > > > trapping
> > > > -* into the hypervisor, so the request should be handled
> > > > immediately.
> > > > -*/
> > > > - while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> > > > - !virtqueue_is_broken(vi->cvq))
> > > > - cpu_relax();
> > > > + virtqueue_wait_for_used(vi->cvq, &tmp);
> > > >
> > > > return vi->ctrl->status == VIRTIO_NET_OK;
> > > > }
> > > > @@ -3524,7 +3525,7 @@ static int virtnet_find_vqs(struct virtnet_info
> > > > *vi)
> > > >
> > > > /* Parameters for control virtqueue, if any */
> > > > if (vi->has_cvq) {
> > > > - callbacks[total_vqs - 1] = NULL;
> > > > + callbacks[total_vqs - 1] = virtnet_cvq_done;
> > >
> > > If we're using CVQ callback, what is the actual use of the timeout?
> >
> > Because we can't sleep forever since locks could be held like RTNL_LOCK.
> >
>
> Right, rtnl_lock kind of invalidates it for a general case.
>
> But do all of the commands need to take rtnl_lock? For example I see
> how we could remove it from ctrl_announce,
I think not, it's intended to serialize all cvq commands.
> so lack of ack may not be
> fatal for it.
Then there could be more than one cvq commands sent to the device, the
busy poll logic may not work.
And it's a hint that the device malfunctioned which is something that
the driver should be aware of.
Thanks
> Assuming a buggy device, we can take some cvq commands
> out of this fatal situation.
>
> This series already improves the current situation and my suggestion
> (if it's worth it) can be applied on top of it, so it is not a blocker
> at all.
>
> > >
> > > I'd say there is no right choice neither in the right timeout value
> > > nor in the action to take.
> >
> > In the next version, I tend to put BAD_RING() to prevent future requests.
> >
> > > Why not simply trigger the cmd and do all
> > > the changes at command return?
> >
> > I don't get this, sorry.
> >
>
> It's actually expanding the first point so you already answered it :).
>
> Thanks!
>
> > >
> > > I suspect the reason is that it complicates the code. For example,
> > > having the possibility of many in flight commands, races between their
> > > completion, etc.
> >
> > Actually the cvq command was serialized through RTNL_LOCK, so we don't
> > need to worry about this.
> >
> > In the next version I can add ASSERT_RTNL().
> >
> > Thanks
> >
> > > The virtio standard does not even cover unordered
> > > used commands if I'm not wrong.
> > >
> > > Is there any other fundamental reason?
> > >
> > > Thanks!
> > >
> > > > names[total_vqs - 1] = "control";
> > > > }
> > > >
> > > > --
> > > > 2.25.1
> > > >
> > >
> >
>
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Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
> This needs to be proposed to the virtio spec first. And actually we > need more than this: > > 1) we still need a way to deal with the device without this feature > 2) driver can't depend solely on what is advertised by the device (e.g > device can choose to advertise a very long timeout) I think that I wasn't clear, sorry. I'm not talking about a new virtio feature, I'm talking about a situation when: * virtio_net issues a control command. * the device gets the command, but somehow, completes the command after timeout. * virtio_net assumes that the command failed (timeout), and issues a different control command. * virtio_net will then call virtqueue_wait_for_used, and will immediately get the previous response (If I'm not wrong). So, this is not a new feature that I'm proposing, just a situation that may occur due to cvq timeouts. Anyhow, your solution calling BAD_RING if we reach a timeout should prevent this situation. Thanks ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
On Thu, Dec 22, 2022 at 5:19 PM Eugenio Perez Martin
wrote:
>
> On Thu, Dec 22, 2022 at 7:05 AM Jason Wang wrote:
> >
> > We used to busy waiting on the cvq command this tends to be
> > problematic since:
> >
> > 1) CPU could wait for ever on a buggy/malicous device
> > 2) There's no wait to terminate the process that triggers the cvq
> >command
> >
> > So this patch switch to use sleep with a timeout (1s) instead of busy
> > polling for the cvq command forever. This gives the scheduler a breath
> > and can let the process can respond to a signal.
> >
> > Signed-off-by: Jason Wang
> > ---
> > drivers/net/virtio_net.c | 15 ---
> > 1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 8225496ccb1e..69173049371f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info
> > *vi)
> > vi->rx_mode_work_enabled = false;
> > spin_unlock_bh(&vi->rx_mode_lock);
> >
> > + virtqueue_wake_up(vi->cvq);
> > flush_work(&vi->rx_mode_work);
> > }
> >
> > @@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi,
> > struct receive_queue *rq,
> > return !oom;
> > }
> >
> > +static void virtnet_cvq_done(struct virtqueue *cvq)
> > +{
> > + virtqueue_wake_up(cvq);
> > +}
> > +
> > static void skb_recv_done(struct virtqueue *rvq)
> > {
> > struct virtnet_info *vi = rvq->vdev->priv;
> > @@ -2024,12 +2030,7 @@ static bool virtnet_send_command(struct virtnet_info
> > *vi, u8 class, u8 cmd,
> > if (unlikely(!virtqueue_kick(vi->cvq)))
> > return vi->ctrl->status == VIRTIO_NET_OK;
> >
> > - /* Spin for a response, the kick causes an ioport write, trapping
> > -* into the hypervisor, so the request should be handled
> > immediately.
> > -*/
> > - while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> > - !virtqueue_is_broken(vi->cvq))
> > - cpu_relax();
> > + virtqueue_wait_for_used(vi->cvq, &tmp);
> >
> > return vi->ctrl->status == VIRTIO_NET_OK;
> > }
> > @@ -3524,7 +3525,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >
> > /* Parameters for control virtqueue, if any */
> > if (vi->has_cvq) {
> > - callbacks[total_vqs - 1] = NULL;
> > + callbacks[total_vqs - 1] = virtnet_cvq_done;
>
> If we're using CVQ callback, what is the actual use of the timeout?
Because we can't sleep forever since locks could be held like RTNL_LOCK.
>
> I'd say there is no right choice neither in the right timeout value
> nor in the action to take.
In the next version, I tend to put BAD_RING() to prevent future requests.
> Why not simply trigger the cmd and do all
> the changes at command return?
I don't get this, sorry.
>
> I suspect the reason is that it complicates the code. For example,
> having the possibility of many in flight commands, races between their
> completion, etc.
Actually the cvq command was serialized through RTNL_LOCK, so we don't
need to worry about this.
In the next version I can add ASSERT_RTNL().
Thanks
> The virtio standard does not even cover unordered
> used commands if I'm not wrong.
>
> Is there any other fundamental reason?
>
> Thanks!
>
> > names[total_vqs - 1] = "control";
> > }
> >
> > --
> > 2.25.1
> >
>
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Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
On Thu, Dec 22, 2022 at 11:55 PM Alvaro Karsz wrote: > > My point is that the device may complete the control command after the > timeout, This needs to be proposed to the virtio spec first. And actually we need more than this: 1) we still need a way to deal with the device without this feature 2) driver can't depend solely on what is advertised by the device (e.g device can choose to advertise a very long timeout) > so, if I'm not mistaken, next time we send a control command and call > virtqueue_wait_for_used we'll get the previous response. > In the next version, I will first put BAD_RING() to prevent future requests for cvq. Note that the patch can't fix all the issues, we need more things on top. But it's a good step and it will behave much better than the current code. Thanks ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
My point is that the device may complete the control command after the timeout, so, if I'm not mistaken, next time we send a control command and call virtqueue_wait_for_used we'll get the previous response. ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
Hi Alvaro: On Thu, Dec 22, 2022 at 2:44 PM Alvaro Karsz wrote: > > Hi Jason, > > Adding timeout to the cvq is a great idea IMO. > > > - /* Spin for a response, the kick causes an ioport write, trapping > > -* into the hypervisor, so the request should be handled > > immediately. > > -*/ > > - while (!virtqueue_get_buf(vi->cvq, &tmp) && > > - !virtqueue_is_broken(vi->cvq)) > > - cpu_relax(); > > + virtqueue_wait_for_used(vi->cvq, &tmp); > > Do you think that we should continue like nothing happened in case of a > timeout? We could, but we should not depend on a device to do this since it's not reliable. More below. > Shouldn't we reset the device? We can't depend on device, there's probably another loop in reset(): E.g in vp_reset() we had: while (vp_modern_get_status(mdev)) msleep(1); > What happens if a device completes the control command after timeout? Maybe we could have a BAD_RING() here in this case (and more check in vq->broken in this case). Thanks > > Thanks > > Alvaro > ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
Hi Jason, Adding timeout to the cvq is a great idea IMO. > - /* Spin for a response, the kick causes an ioport write, trapping > -* into the hypervisor, so the request should be handled immediately. > -*/ > - while (!virtqueue_get_buf(vi->cvq, &tmp) && > - !virtqueue_is_broken(vi->cvq)) > - cpu_relax(); > + virtqueue_wait_for_used(vi->cvq, &tmp); Do you think that we should continue like nothing happened in case of a timeout? Shouldn't we reset the device? What happens if a device completes the control command after timeout? Thanks Alvaro ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
[RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
We used to busy waiting on the cvq command this tends to be
problematic since:
1) CPU could wait for ever on a buggy/malicous device
2) There's no wait to terminate the process that triggers the cvq
command
So this patch switch to use sleep with a timeout (1s) instead of busy
polling for the cvq command forever. This gives the scheduler a breath
and can let the process can respond to a signal.
Signed-off-by: Jason Wang
---
drivers/net/virtio_net.c | 15 ---
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 8225496ccb1e..69173049371f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -405,6 +405,7 @@ static void disable_rx_mode_work(struct virtnet_info *vi)
vi->rx_mode_work_enabled = false;
spin_unlock_bh(&vi->rx_mode_lock);
+ virtqueue_wake_up(vi->cvq);
flush_work(&vi->rx_mode_work);
}
@@ -1497,6 +1498,11 @@ static bool try_fill_recv(struct virtnet_info *vi,
struct receive_queue *rq,
return !oom;
}
+static void virtnet_cvq_done(struct virtqueue *cvq)
+{
+ virtqueue_wake_up(cvq);
+}
+
static void skb_recv_done(struct virtqueue *rvq)
{
struct virtnet_info *vi = rvq->vdev->priv;
@@ -2024,12 +2030,7 @@ static bool virtnet_send_command(struct virtnet_info
*vi, u8 class, u8 cmd,
if (unlikely(!virtqueue_kick(vi->cvq)))
return vi->ctrl->status == VIRTIO_NET_OK;
- /* Spin for a response, the kick causes an ioport write, trapping
-* into the hypervisor, so the request should be handled immediately.
-*/
- while (!virtqueue_get_buf(vi->cvq, &tmp) &&
- !virtqueue_is_broken(vi->cvq))
- cpu_relax();
+ virtqueue_wait_for_used(vi->cvq, &tmp);
return vi->ctrl->status == VIRTIO_NET_OK;
}
@@ -3524,7 +3525,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
/* Parameters for control virtqueue, if any */
if (vi->has_cvq) {
- callbacks[total_vqs - 1] = NULL;
+ callbacks[total_vqs - 1] = virtnet_cvq_done;
names[total_vqs - 1] = "control";
}
--
2.25.1
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