| Message ID | 20170526142858.19931-4-maxime.coquelin@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: > Vhost-kernel backend need needs > to receive IOTLB entry for used ring > information early, which is done by triggering a miss event on > its address. > > This patch extends this behaviour to all rings information, to be > compatible with vhost-user backend design. Why does vhost-user need it though? > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> > --- > v2: > - Revert back to existing behaviour, i.e. only send IOTLB updates > at ring enablement time, not at ring address setting time (mst). > - Extend IOTLB misses to all ring addresses, not only used ring. > > hw/virtio/vhost.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index 6eddb09..7867034 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) > if (vhost_dev_has_iommu(hdev)) { > hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); > > - /* Update used ring information for IOTLB to work correctly, > - * vhost-kernel code requires for this.*/ > + /* > + * Update rings information for IOTLB to work correctly, > + * vhost-kernel and vhost-user codes require for this. Better just say "Update ring info for vhost iotlb." The rest isn't really informative. > + */ > for (i = 0; i < hdev->nvqs; ++i) { > struct vhost_virtqueue *vq = hdev->vqs + i; > vhost_device_iotlb_miss(hdev, vq->used_phys, true); > + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); > + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); So I don't remember why does vhost in kernel want miss on used at start time. Jason, could you comment on this please? > } > } > return 0; > -- > 2.9.4
Hi Michael, On 05/30/2017 08:12 PM, Michael S. Tsirkin wrote: > On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: >> Vhost-kernel backend need > > needs > >> to receive IOTLB entry for used ring >> information early, which is done by triggering a miss event on >> its address. >> >> This patch extends this behaviour to all rings information, to be >> compatible with vhost-user backend design. > > Why does vhost-user need it though? For vhost-user, this simplifies the backend design because generally, the backend sends IOTLB miss requests from processing threads through the slave channel, and receives resulting IOTLB updates in vhost-user protocol thread. The only exception is for these rings info, where IOTLB miss requests are sent from vhost-user protocol thread (in the SET_VRING_ENABLE request handler), so the resulting IOTLB update is only handled by the backend when the rings are enabled, which is too late. It could be possible to overcome this issue, but I think it would make the design more complex or less efficient. I see several options: 1. Change the IOTLB miss request so that the master sends the IOTLB update as reply, instead of the reply-ack. It would mean that IOTLB updates/invalidations would be sent either via the master channel or the slave channel. On QEMU side, it means diverging from kernel backend implementation. On backend side, it means having possibly multiple threads writing to the IOTLB cache. 2. In vhost-user protocol thread, when handling SET_VRING_ENABLE, send IOTLB miss request without setting the reply-ack flag, and poll the vhost-user socket to read the resulting IOTLB update. The problem is that other requests could be pending in the socket's buffer, and so it would end-up nesting multiple requests handling. 3. Don't interpret rings info in the vhost-user protocol thread, but only in the processing threads. The advantage is that it would address the remark you made on patch 6 that invalidates are not affecting ring info. The downside being the overhead induced by checking whether the ring info are valid every time it is being used. I haven't prototyped this solution, but I expected the performance regression to be a blocker. 4. In SET_VRING_ENABLE, don't enable the ring if needed entries are not in IOTLB cache. Just send the IOTLB misses without reply-ack flag and postpone enable when handling IOTLB updates. It will be a little more complex solution than current one, but it may be the less impacting compared to the other 3 options. Thinking again, maybe trying solution would be worth the effort, and could be extended also to disable the rings when receiving invalidates that affect rings info. What do you think? > >> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> >> --- >> v2: >> - Revert back to existing behaviour, i.e. only send IOTLB updates >> at ring enablement time, not at ring address setting time (mst). >> - Extend IOTLB misses to all ring addresses, not only used ring. >> >> hw/virtio/vhost.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >> index 6eddb09..7867034 100644 >> --- a/hw/virtio/vhost.c >> +++ b/hw/virtio/vhost.c >> @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) >> if (vhost_dev_has_iommu(hdev)) { >> hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); >> >> - /* Update used ring information for IOTLB to work correctly, >> - * vhost-kernel code requires for this.*/ >> + /* >> + * Update rings information for IOTLB to work correctly, >> + * vhost-kernel and vhost-user codes require for this. > > Better just say "Update ring info for vhost iotlb." > > The rest isn't really informative. Ok. > > > >> + */ >> for (i = 0; i < hdev->nvqs; ++i) { >> struct vhost_virtqueue *vq = hdev->vqs + i; >> vhost_device_iotlb_miss(hdev, vq->used_phys, true); >> + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); >> + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); > > So I don't remember why does vhost in kernel want miss on used > at start time. > > Jason, could you comment on this please? > > > >> } >> } >> return 0; >> -- >> 2.9.4 Thanks, Maxime
On 05/30/2017 11:06 PM, Maxime Coquelin wrote: > Hi Michael, > > On 05/30/2017 08:12 PM, Michael S. Tsirkin wrote: >> On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: >>> Vhost-kernel backend need >> >> needs >> >>> to receive IOTLB entry for used ring >>> information early, which is done by triggering a miss event on >>> its address. >>> >>> This patch extends this behaviour to all rings information, to be >>> compatible with vhost-user backend design. >> >> Why does vhost-user need it though? > > For vhost-user, this simplifies the backend design because generally, > the backend sends IOTLB miss requests from processing threads through > the slave channel, and receives resulting IOTLB updates in vhost-user > protocol thread. > > The only exception is for these rings info, where IOTLB miss requests > are sent from vhost-user protocol thread (in the SET_VRING_ENABLE > request handler), so the resulting IOTLB update is only handled by > the backend when the rings are enabled, which is too late. > > It could be possible to overcome this issue, but I think it would > make the design more complex or less efficient. I see several options: > > 1. Change the IOTLB miss request so that the master sends the IOTLB > update as reply, instead of the reply-ack. It would mean that IOTLB > updates/invalidations would be sent either via the master channel or > the slave channel. On QEMU side, it means diverging from kernel backend > implementation. On backend side, it means having possibly multiple > threads writing to the IOTLB cache. > > 2. In vhost-user protocol thread, when handling SET_VRING_ENABLE, send > IOTLB miss request without setting the reply-ack flag, and poll the > vhost-user socket to read the resulting IOTLB update. The problem is > that other requests could be pending in the socket's buffer, and so it > would end-up nesting multiple requests handling. > > 3. Don't interpret rings info in the vhost-user protocol thread, but > only in the processing threads. The advantage is that it would address > the remark you made on patch 6 that invalidates are not affecting ring > info. The downside being the overhead induced by checking whether the > ring info are valid every time it is being used. I haven't prototyped > this solution, but I expected the performance regression to be a > blocker. > > 4. In SET_VRING_ENABLE, don't enable the ring if needed entries are not > in IOTLB cache. Just send the IOTLB misses without reply-ack flag and > postpone enable when handling IOTLB updates. It will be a little more > complex solution than current one, but it may be the less impacting > compared to the other 3 options. > > > Thinking again, maybe trying solution would be worth the effort, and s/solution/solution 4/ > could be extended also to disable the rings when receiving invalidates > that affect rings info. > > What do you think? > >> >>> >>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> >>> --- >>> v2: >>> - Revert back to existing behaviour, i.e. only send IOTLB updates >>> at ring enablement time, not at ring address setting time (mst). >>> - Extend IOTLB misses to all ring addresses, not only used ring. >>> >>> hw/virtio/vhost.c | 8 ++++++-- >>> 1 file changed, 6 insertions(+), 2 deletions(-) >>> >>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>> index 6eddb09..7867034 100644 >>> --- a/hw/virtio/vhost.c >>> +++ b/hw/virtio/vhost.c >>> @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, >>> VirtIODevice *vdev) >>> if (vhost_dev_has_iommu(hdev)) { >>> hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); >>> - /* Update used ring information for IOTLB to work correctly, >>> - * vhost-kernel code requires for this.*/ >>> + /* >>> + * Update rings information for IOTLB to work correctly, >>> + * vhost-kernel and vhost-user codes require for this. >> >> Better just say "Update ring info for vhost iotlb." >> >> The rest isn't really informative. > > Ok. > >> >> >> >>> + */ >>> for (i = 0; i < hdev->nvqs; ++i) { >>> struct vhost_virtqueue *vq = hdev->vqs + i; >>> vhost_device_iotlb_miss(hdev, vq->used_phys, true); >>> + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); >>> + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); >> >> So I don't remember why does vhost in kernel want miss on used >> at start time. >> >> Jason, could you comment on this please? >> >> >> >>> } >>> } >>> return 0; >>> -- >>> 2.9.4 > > Thanks, > Maxime
On 2017年05月31日 02:12, Michael S. Tsirkin wrote: > On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: >> Vhost-kernel backend need > needs > >> to receive IOTLB entry for used ring >> information early, which is done by triggering a miss event on >> its address. >> >> This patch extends this behaviour to all rings information, to be >> compatible with vhost-user backend design. > Why does vhost-user need it though? > >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> >> --- >> v2: >> - Revert back to existing behaviour, i.e. only send IOTLB updates >> at ring enablement time, not at ring address setting time (mst). >> - Extend IOTLB misses to all ring addresses, not only used ring. >> >> hw/virtio/vhost.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >> index 6eddb09..7867034 100644 >> --- a/hw/virtio/vhost.c >> +++ b/hw/virtio/vhost.c >> @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) >> if (vhost_dev_has_iommu(hdev)) { >> hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); >> >> - /* Update used ring information for IOTLB to work correctly, >> - * vhost-kernel code requires for this.*/ >> + /* >> + * Update rings information for IOTLB to work correctly, >> + * vhost-kernel and vhost-user codes require for this. > Better just say "Update ring info for vhost iotlb." > > The rest isn't really informative. > > > >> + */ >> for (i = 0; i < hdev->nvqs; ++i) { >> struct vhost_virtqueue *vq = hdev->vqs + i; >> vhost_device_iotlb_miss(hdev, vq->used_phys, true); >> + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); >> + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); > So I don't remember why does vhost in kernel want miss on used > at start time. > > Jason, could you comment on this please? In vhost_vq_init_access() we try to update used flags and fetch last_used_idx, this requires we cache its translation in advance. We don't support IOTLB miss on control path (ioctl) now, so I choose to update IOTLB. Thanks > > > >> } >> } >> return 0; >> -- >> 2.9.4
Hi Michael, On 05/30/2017 11:11 PM, Maxime Coquelin wrote: > > > On 05/30/2017 11:06 PM, Maxime Coquelin wrote: >> Hi Michael, >> >> On 05/30/2017 08:12 PM, Michael S. Tsirkin wrote: >>> On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: >>>> Vhost-kernel backend need >>> >>> needs >>> >>>> to receive IOTLB entry for used ring >>>> information early, which is done by triggering a miss event on >>>> its address. >>>> >>>> This patch extends this behaviour to all rings information, to be >>>> compatible with vhost-user backend design. >>> >>> Why does vhost-user need it though? >> >> For vhost-user, this simplifies the backend design because generally, >> the backend sends IOTLB miss requests from processing threads through >> the slave channel, and receives resulting IOTLB updates in vhost-user >> protocol thread. >> >> The only exception is for these rings info, where IOTLB miss requests >> are sent from vhost-user protocol thread (in the SET_VRING_ENABLE >> request handler), so the resulting IOTLB update is only handled by >> the backend when the rings are enabled, which is too late. >> >> It could be possible to overcome this issue, but I think it would >> make the design more complex or less efficient. I see several options: >> >> 1. Change the IOTLB miss request so that the master sends the IOTLB >> update as reply, instead of the reply-ack. It would mean that IOTLB >> updates/invalidations would be sent either via the master channel or >> the slave channel. On QEMU side, it means diverging from kernel backend >> implementation. On backend side, it means having possibly multiple >> threads writing to the IOTLB cache. >> >> 2. In vhost-user protocol thread, when handling SET_VRING_ENABLE, send >> IOTLB miss request without setting the reply-ack flag, and poll the >> vhost-user socket to read the resulting IOTLB update. The problem is >> that other requests could be pending in the socket's buffer, and so it >> would end-up nesting multiple requests handling. >> >> 3. Don't interpret rings info in the vhost-user protocol thread, but >> only in the processing threads. The advantage is that it would address >> the remark you made on patch 6 that invalidates are not affecting ring >> info. The downside being the overhead induced by checking whether the >> ring info are valid every time it is being used. I haven't prototyped >> this solution, but I expected the performance regression to be a >> blocker. >> >> 4. In SET_VRING_ENABLE, don't enable the ring if needed entries are >> not in IOTLB cache. Just send the IOTLB misses without reply-ack flag >> and postpone enable when handling IOTLB updates. It will be a little >> more complex solution than current one, but it may be the less >> impacting compared to the other 3 options. >> >> >> Thinking again, maybe trying solution would be worth the effort, and > > s/solution/solution 4/ > >> could be extended also to disable the rings when receiving invalidates >> that affect rings info. >> >> What do you think? I have made some tests to see if solution 4 would work, and while it could work most of the times, it is really fragile as deadlock would happen if either slave or master sockets buffers are full. This is issue also impact solution 1 above. Regards, Maxime
On Tue, May 30, 2017 at 11:06:54PM +0200, Maxime Coquelin wrote: > Hi Michael, > > On 05/30/2017 08:12 PM, Michael S. Tsirkin wrote: > > On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: > > > Vhost-kernel backend need > > > > needs > > > > > to receive IOTLB entry for used ring > > > information early, which is done by triggering a miss event on > > > its address. > > > > > > This patch extends this behaviour to all rings information, to be > > > compatible with vhost-user backend design. > > > > Why does vhost-user need it though? > > For vhost-user, this simplifies the backend design because generally, > the backend sends IOTLB miss requests from processing threads through > the slave channel, and receives resulting IOTLB updates in vhost-user > protocol thread. > > The only exception is for these rings info, where IOTLB miss requests > are sent from vhost-user protocol thread (in the SET_VRING_ENABLE > request handler), so the resulting IOTLB update is only handled by > the backend when the rings are enabled, which is too late. > > It could be possible to overcome this issue, but I think it would > make the design more complex or less efficient. I see several options: > > 1. Change the IOTLB miss request so that the master sends the IOTLB > update as reply, instead of the reply-ack. It would mean that IOTLB > updates/invalidations would be sent either via the master channel or > the slave channel. On QEMU side, it means diverging from kernel backend > implementation. On backend side, it means having possibly multiple > threads writing to the IOTLB cache. > > 2. In vhost-user protocol thread, when handling SET_VRING_ENABLE, send > IOTLB miss request without setting the reply-ack flag, and poll the > vhost-user socket to read the resulting IOTLB update. The problem is > that other requests could be pending in the socket's buffer, and so it > would end-up nesting multiple requests handling. > > 3. Don't interpret rings info in the vhost-user protocol thread, but > only in the processing threads. The advantage is that it would address > the remark you made on patch 6 that invalidates are not affecting ring > info. The downside being the overhead induced by checking whether the > ring info are valid every time it is being used. I haven't prototyped > this solution, but I expected the performance regression to be a > blocker. > > 4. In SET_VRING_ENABLE, don't enable the ring if needed entries are not in > IOTLB cache. Just send the IOTLB misses without reply-ack flag and postpone > enable when handling IOTLB updates. It will be a little more complex > solution than current one, but it may be the less impacting compared to the > other 3 options. > > > Thinking again, maybe trying solution would be worth the effort, and could > be extended also to disable the rings when receiving invalidates > that affect rings info. > > What do you think? I'm fine with 3 or 4 generally. But pls note that if the ring crosses a page boundary (e.g. ring size > page size) and when not using hugetlbfs, there is no guarantee a single DMA address covers the whole ring. > > > > > > > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> > > > --- > > > v2: > > > - Revert back to existing behaviour, i.e. only send IOTLB updates > > > at ring enablement time, not at ring address setting time (mst). > > > - Extend IOTLB misses to all ring addresses, not only used ring. > > > > > > hw/virtio/vhost.c | 8 ++++++-- > > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > > > index 6eddb09..7867034 100644 > > > --- a/hw/virtio/vhost.c > > > +++ b/hw/virtio/vhost.c > > > @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) > > > if (vhost_dev_has_iommu(hdev)) { > > > hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); > > > - /* Update used ring information for IOTLB to work correctly, > > > - * vhost-kernel code requires for this.*/ > > > + /* > > > + * Update rings information for IOTLB to work correctly, > > > + * vhost-kernel and vhost-user codes require for this. > > > > Better just say "Update ring info for vhost iotlb." > > > > The rest isn't really informative. > > Ok. > > > > > > > > > > + */ > > > for (i = 0; i < hdev->nvqs; ++i) { > > > struct vhost_virtqueue *vq = hdev->vqs + i; > > > vhost_device_iotlb_miss(hdev, vq->used_phys, true); > > > + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); > > > + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); > > > > So I don't remember why does vhost in kernel want miss on used > > at start time. > > > > Jason, could you comment on this please? > > > > > > > > > } > > > } > > > return 0; > > > -- > > > 2.9.4 > > Thanks, > Maxime
On Wed, May 31, 2017 at 05:20:21PM +0200, Maxime Coquelin wrote: > Hi Michael, > > On 05/30/2017 11:11 PM, Maxime Coquelin wrote: > > > > > > On 05/30/2017 11:06 PM, Maxime Coquelin wrote: > > > Hi Michael, > > > > > > On 05/30/2017 08:12 PM, Michael S. Tsirkin wrote: > > > > On Fri, May 26, 2017 at 04:28:55PM +0200, Maxime Coquelin wrote: > > > > > Vhost-kernel backend need > > > > > > > > needs > > > > > > > > > to receive IOTLB entry for used ring > > > > > information early, which is done by triggering a miss event on > > > > > its address. > > > > > > > > > > This patch extends this behaviour to all rings information, to be > > > > > compatible with vhost-user backend design. > > > > > > > > Why does vhost-user need it though? > > > > > > For vhost-user, this simplifies the backend design because generally, > > > the backend sends IOTLB miss requests from processing threads through > > > the slave channel, and receives resulting IOTLB updates in vhost-user > > > protocol thread. > > > > > > The only exception is for these rings info, where IOTLB miss requests > > > are sent from vhost-user protocol thread (in the SET_VRING_ENABLE > > > request handler), so the resulting IOTLB update is only handled by > > > the backend when the rings are enabled, which is too late. > > > > > > It could be possible to overcome this issue, but I think it would > > > make the design more complex or less efficient. I see several options: > > > > > > 1. Change the IOTLB miss request so that the master sends the IOTLB > > > update as reply, instead of the reply-ack. It would mean that IOTLB > > > updates/invalidations would be sent either via the master channel or > > > the slave channel. On QEMU side, it means diverging from kernel backend > > > implementation. On backend side, it means having possibly multiple > > > threads writing to the IOTLB cache. > > > > > > 2. In vhost-user protocol thread, when handling SET_VRING_ENABLE, send > > > IOTLB miss request without setting the reply-ack flag, and poll the > > > vhost-user socket to read the resulting IOTLB update. The problem is > > > that other requests could be pending in the socket's buffer, and so it > > > would end-up nesting multiple requests handling. > > > > > > 3. Don't interpret rings info in the vhost-user protocol thread, but > > > only in the processing threads. The advantage is that it would address > > > the remark you made on patch 6 that invalidates are not affecting ring > > > info. The downside being the overhead induced by checking whether the > > > ring info are valid every time it is being used. I haven't prototyped > > > this solution, but I expected the performance regression to be a > > > blocker. > > > > > > 4. In SET_VRING_ENABLE, don't enable the ring if needed entries are > > > not in IOTLB cache. Just send the IOTLB misses without reply-ack > > > flag and postpone enable when handling IOTLB updates. It will be a > > > little more complex solution than current one, but it may be the > > > less impacting compared to the other 3 options. > > > > > > > > > Thinking again, maybe trying solution would be worth the effort, and > > > > s/solution/solution 4/ > > > > > could be extended also to disable the rings when receiving invalidates > > > that affect rings info. > > > > > > What do you think? > > I have made some tests to see if solution 4 would work, and while it > could work most of the times, it is really fragile as deadlock would > happen if either slave or master sockets buffers are full. This is issue > also impact solution 1 above. > > Regards, > Maxime Pls try 3 above. I don't see why would a single conditional branch be so expensive.
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index 6eddb09..7867034 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -1552,11 +1552,15 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev) if (vhost_dev_has_iommu(hdev)) { hdev->vhost_ops->vhost_set_iotlb_callback(hdev, true); - /* Update used ring information for IOTLB to work correctly, - * vhost-kernel code requires for this.*/ + /* + * Update rings information for IOTLB to work correctly, + * vhost-kernel and vhost-user codes require for this. + */ for (i = 0; i < hdev->nvqs; ++i) { struct vhost_virtqueue *vq = hdev->vqs + i; vhost_device_iotlb_miss(hdev, vq->used_phys, true); + vhost_device_iotlb_miss(hdev, vq->desc_phys, true); + vhost_device_iotlb_miss(hdev, vq->avail_phys, true); } } return 0;
Vhost-kernel backend need to receive IOTLB entry for used ring information early, which is done by triggering a miss event on its address. This patch extends this behaviour to all rings information, to be compatible with vhost-user backend design. Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> --- v2: - Revert back to existing behaviour, i.e. only send IOTLB updates at ring enablement time, not at ring address setting time (mst). - Extend IOTLB misses to all ring addresses, not only used ring. hw/virtio/vhost.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)