* [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists @ 2025-12-11 9:05 Aaron Lo 2025-12-11 13:14 ` Michael S. Tsirkin 2025-12-11 14:22 ` Daniel P. Berrangé 0 siblings, 2 replies; 5+ messages in thread From: Aaron Lo @ 2025-12-11 9:05 UTC (permalink / raw) To: qemu-devel; +Cc: Michael S. Tsirkin, David Hildenbrand, qemu-trivial, Aaron Lo The VirtIO specification (section 5.5.2) states that the stats queue is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is negotiated. QEMU currently creates the statsq unconditionally. This patch guards statsq creation so it occurs only when the feature bit is enabled. Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 Signed-off-by: Aaron Lo <aaronlo0929@gmail.com> --- hw/virtio/virtio-balloon.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index 02cdd807d7..f5d4d5f60c 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); - s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); + + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_STATS_VQ)) { + s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); + } if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize(DeviceState *dev) virtio_delete_queue(s->ivq); virtio_delete_queue(s->dvq); - virtio_delete_queue(s->svq); + if (s->svq) { + virtio_delete_queue(s->svq); + } if (s->free_page_vq) { virtio_delete_queue(s->free_page_vq); } --- base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 change-id: 20251211-balloon-check-stats-feature-7ea658e038ce Best regards, -- Aaron Lo <aaronlo0929@gmail.com> ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists 2025-12-11 9:05 [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists Aaron Lo @ 2025-12-11 13:14 ` Michael S. Tsirkin 2025-12-11 14:22 ` Daniel P. Berrangé 1 sibling, 0 replies; 5+ messages in thread From: Michael S. Tsirkin @ 2025-12-11 13:14 UTC (permalink / raw) To: Aaron Lo; +Cc: qemu-devel, David Hildenbrand, qemu-trivial On Thu, Dec 11, 2025 at 03:05:49AM -0600, Aaron Lo wrote: > The VirtIO specification (section 5.5.2) states that the stats queue > is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is > negotiated. QEMU currently creates the statsq unconditionally. > > This patch guards statsq creation so it occurs only when the > feature bit is enabled. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 > > Signed-off-by: Aaron Lo <aaronlo0929@gmail.com> did you test this with linux guests and with free page hinting? The issue is that sadly everyone is out of spec here. We will have to fix the spec. > --- > hw/virtio/virtio-balloon.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index 02cdd807d7..f5d4d5f60c 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) > > s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > - s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > + > + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_STATS_VQ)) { > + s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > + } > > if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, > @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize(DeviceState *dev) > > virtio_delete_queue(s->ivq); > virtio_delete_queue(s->dvq); > - virtio_delete_queue(s->svq); > + if (s->svq) { > + virtio_delete_queue(s->svq); > + } > if (s->free_page_vq) { > virtio_delete_queue(s->free_page_vq); > } > > --- > base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 > change-id: 20251211-balloon-check-stats-feature-7ea658e038ce > > Best regards, > -- > Aaron Lo <aaronlo0929@gmail.com> ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists 2025-12-11 9:05 [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists Aaron Lo 2025-12-11 13:14 ` Michael S. Tsirkin @ 2025-12-11 14:22 ` Daniel P. Berrangé 2025-12-11 20:15 ` Aaron Lo 1 sibling, 1 reply; 5+ messages in thread From: Daniel P. Berrangé @ 2025-12-11 14:22 UTC (permalink / raw) To: Aaron Lo; +Cc: qemu-devel, Michael S. Tsirkin, David Hildenbrand, qemu-trivial On Thu, Dec 11, 2025 at 03:05:49AM -0600, Aaron Lo wrote: > The VirtIO specification (section 5.5.2) states that the stats queue > is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is > negotiated. QEMU currently creates the statsq unconditionally. > > This patch guards statsq creation so it occurs only when the > feature bit is enabled. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 > > Signed-off-by: Aaron Lo <aaronlo0929@gmail.com> > --- > hw/virtio/virtio-balloon.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index 02cdd807d7..f5d4d5f60c 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) > > s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > - s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > + > + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_STATS_VQ)) { > + s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > + } This seems like a change that is liable to break live migration state compatibility, as IIUC the queues are encoded in the state ? > > if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, > @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize(DeviceState *dev) > > virtio_delete_queue(s->ivq); > virtio_delete_queue(s->dvq); > - virtio_delete_queue(s->svq); > + if (s->svq) { > + virtio_delete_queue(s->svq); > + } > if (s->free_page_vq) { > virtio_delete_queue(s->free_page_vq); > } > > --- > base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 > change-id: 20251211-balloon-check-stats-feature-7ea658e038ce > > Best regards, > -- > Aaron Lo <aaronlo0929@gmail.com> > > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists 2025-12-11 14:22 ` Daniel P. Berrangé @ 2025-12-11 20:15 ` Aaron Lo 2025-12-11 22:18 ` Michael S. Tsirkin 0 siblings, 1 reply; 5+ messages in thread From: Aaron Lo @ 2025-12-11 20:15 UTC (permalink / raw) To: "Daniel P. Berrangé" Cc: qemu-devel, Michael S. Tsirkin, David Hildenbrand, qemu-trivial [-- Attachment #1: Type: text/plain, Size: 2897 bytes --] Hi Daniel and Michael, Thanks for the quick feedback. Given the migration concerns and issues with the spec itself, I think it’ll be best to drop the code changes for now. Thanks again for the guidance, Aaron > On Dec 11, 2025, at 8:22 AM, Daniel P. Berrangé <berrange@redhat.com> wrote: > > On Thu, Dec 11, 2025 at 03:05:49AM -0600, Aaron Lo wrote: >> The VirtIO specification (section 5.5.2) states that the stats queue >> is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is >> negotiated. QEMU currently creates the statsq unconditionally. >> >> This patch guards statsq creation so it occurs only when the >> feature bit is enabled. >> >> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 >> >> Signed-off-by: Aaron Lo <aaronlo0929@gmail.com> >> --- >> hw/virtio/virtio-balloon.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c >> index 02cdd807d7..f5d4d5f60c 100644 >> --- a/hw/virtio/virtio-balloon.c >> +++ b/hw/virtio/virtio-balloon.c >> @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) >> >> s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); >> s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); >> - s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); >> + >> + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_STATS_VQ)) { >> + s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); >> + } > > This seems like a change that is liable to break live migration > state compatibility, as IIUC the queues are encoded in the state ? > >> >> if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { >> s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, >> @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize(DeviceState *dev) >> >> virtio_delete_queue(s->ivq); >> virtio_delete_queue(s->dvq); >> - virtio_delete_queue(s->svq); >> + if (s->svq) { >> + virtio_delete_queue(s->svq); >> + } >> if (s->free_page_vq) { >> virtio_delete_queue(s->free_page_vq); >> } >> >> --- >> base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 >> change-id: 20251211-balloon-check-stats-feature-7ea658e038ce >> >> Best regards, >> -- >> Aaron Lo <aaronlo0929@gmail.com> >> >> > > With regards, > Daniel > -- > |: https://berrange.com <https://berrange.com/> -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org <https://libvirt.org/> -o- https://fstop138.berrange.com <https://fstop138.berrange.com/> :| > |: https://entangle-photo.org <https://entangle-photo.org/> -o- https://www.instagram.com/dberrange :| [-- Attachment #2: Type: text/html, Size: 16197 bytes --] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists 2025-12-11 20:15 ` Aaron Lo @ 2025-12-11 22:18 ` Michael S. Tsirkin 0 siblings, 0 replies; 5+ messages in thread From: Michael S. Tsirkin @ 2025-12-11 22:18 UTC (permalink / raw) To: Aaron Lo Cc: "Daniel P. Berrangé", qemu-devel, David Hildenbrand, qemu-trivial On Thu, Dec 11, 2025 at 02:15:58PM -0600, Aaron Lo wrote: > Hi Daniel and Michael, > > Thanks for the quick feedback. > > Given the migration concerns and issues with the spec itself, I think it’ll be > best to drop the code changes for now. > > Thanks again for the guidance, > Aaron You can do the spec changes though ;) > > On Dec 11, 2025, at 8:22 AM, Daniel P. Berrangé <berrange@redhat.com> > wrote: > > On Thu, Dec 11, 2025 at 03:05:49AM -0600, Aaron Lo wrote: > > The VirtIO specification (section 5.5.2) states that the stats queue > is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is > negotiated. QEMU currently creates the statsq unconditionally. > > This patch guards statsq creation so it occurs only when the > feature bit is enabled. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 > > Signed-off-by: Aaron Lo <aaronlo0929@gmail.com> > --- > hw/virtio/virtio-balloon.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index 02cdd807d7..f5d4d5f60c 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize > (DeviceState *dev, Error **errp) > > s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > - s->svq = virtio_add_queue(vdev, 128, > virtio_balloon_receive_stats); > + > + if (virtio_has_feature(s->host_features, > VIRTIO_BALLOON_F_STATS_VQ)) { > + s->svq = virtio_add_queue(vdev, 128, > virtio_balloon_receive_stats); > + } > > > This seems like a change that is liable to break live migration > state compatibility, as IIUC the queues are encoded in the state ? > > > > if (virtio_has_feature(s->host_features, > VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, > @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize > (DeviceState *dev) > > virtio_delete_queue(s->ivq); > virtio_delete_queue(s->dvq); > - virtio_delete_queue(s->svq); > + if (s->svq) { > + virtio_delete_queue(s->svq); > + } > if (s->free_page_vq) { > virtio_delete_queue(s->free_page_vq); > } > > --- > base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 > change-id: 20251211-balloon-check-stats-feature-7ea658e038ce > > Best regards, > -- > Aaron Lo <aaronlo0929@gmail.com> > > > > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange > :| > |: https://libvirt.org -o- https://fstop138.berrange.com > :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange > :| > > ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2025-12-11 22:19 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2025-12-11 9:05 [PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists Aaron Lo 2025-12-11 13:14 ` Michael S. Tsirkin 2025-12-11 14:22 ` Daniel P. Berrangé 2025-12-11 20:15 ` Aaron Lo 2025-12-11 22:18 ` Michael S. Tsirkin
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