On 2025/04/10 22:45, Michael S. Tsirkin wrote:
On Thu, Apr 10, 2025 at 05:26:47PM +0900, Akihiko Odaki wrote:
On 2025/04/10 17:02, Michael S. Tsirkin wrote:
On Thu, Apr 10, 2025 at 04:54:41PM +0900, Akihiko Odaki wrote:
On 2025/04/10 16:48, 'Michael S. Tsirkin' via devel wrote:
On Thu, Apr 10, 2025 at 04:42:06PM +0900, Akihiko Odaki wrote:
virtio-net expects set_features() will be called when the feature set
used by the guest changes to update the number of virtqueues. Call it
during reset as reset clears all features and the queues added for
VIRTIO_NET_F_MQ or VIRTIO_NET_F_RSS will need to be removed.
Fixes: f9d6dbf0bf6e ("virtio-net: remove virtio queues if the guest doesn't support
multiqueue")
Buglink: https://issues.redhat.com/browse/RHEL-73842
Cc: qemu-sta...@nongnu.org
Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>
The issue seems specific to virtio net: rset is reset,
it is distict from set features.
Why not just call the necessary functionality from virtio_net_reset?
set_features is currently implemented only in virtio-net; virtio-gpu-base
also have a function set but it only has code to trace. If another device
implements the function in the future, I think the device will also want to
have it called during reset for the same reason with virtio-net.
virtio_reset() also calls set_status to update the status field so calling
set_features() is more aligned with the handling of the status field.
That came to be because writing 0 to status resets the virtio device.
For a while, this was the only way to reset vhost-user so we just
went along with it.
It is possible to have code to send a command to write 0 to status to
vhost-user in reset(), but calling set_status() in virtio_reset() is more
convenient and makes sense as the status is indeed being set to 0. I think
the same reasoning applies to features.
I don't know who makes assumptions that features are only set during
driver setup, though.
This will send an extra VHOST_USER_SET_FEATURES message for vhost-user,
for example.
I want to have a good reason to add this overhead.
This change won't add an extra VHOST_USER_SET_FEATURES message for
vhost-user because QEMU sends one when VIRTIO_CONFIG_S_DRIVER_OK is
being set for status. The only current implementers of set_features()
are virtio-net and virtio-gpu-base.
We may have more implementers of set_features() in the future though so
it can be worth to think of the semantics of set_features() before that.
When thinking of that, I found the current semantics of set_features()
is not aligned with set_status(), which is confusing. I hope changing
this in virtio_reset() will eliminate this source of confusion and
prevents a bug like what virtio-net has in the future.
---
hw/virtio/virtio.c | 86
+++++++++++++++++++++++++++---------------------------
1 file changed, 43 insertions(+), 43 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 85110bce3744..033e87cdd3b9 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2316,49 +2316,6 @@ void virtio_queue_enable(VirtIODevice *vdev, uint32_t
queue_index)
}
}
-void virtio_reset(void *opaque)
-{
- VirtIODevice *vdev = opaque;
- VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
- int i;
-
- virtio_set_status(vdev, 0);
- if (current_cpu) {
- /* Guest initiated reset */
- vdev->device_endian = virtio_current_cpu_endian();
- } else {
- /* System reset */
- vdev->device_endian = virtio_default_endian();
- }
-
- if (k->get_vhost) {
- struct vhost_dev *hdev = k->get_vhost(vdev);
- /* Only reset when vhost back-end is connected */
- if (hdev && hdev->vhost_ops) {
- vhost_reset_device(hdev);
- }
- }
-
- if (k->reset) {
- k->reset(vdev);
- }
-
- vdev->start_on_kick = false;
- vdev->started = false;
- vdev->broken = false;
- vdev->guest_features = 0;
- vdev->queue_sel = 0;
- vdev->status = 0;
- vdev->disabled = false;
- qatomic_set(&vdev->isr, 0);
- vdev->config_vector = VIRTIO_NO_VECTOR;
- virtio_notify_vector(vdev, vdev->config_vector);
-
- for(i = 0; i < VIRTIO_QUEUE_MAX; i++) {
- __virtio_queue_reset(vdev, i);
- }
-}
-
void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr)
{
if (!vdev->vq[n].vring.num) {
@@ -3169,6 +3126,49 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
return ret;
}
+void virtio_reset(void *opaque)
+{
+ VirtIODevice *vdev = opaque;
+ VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
+ int i;
+
+ virtio_set_status(vdev, 0);
+ if (current_cpu) {
+ /* Guest initiated reset */
+ vdev->device_endian = virtio_current_cpu_endian();
+ } else {
+ /* System reset */
+ vdev->device_endian = virtio_default_endian();
+ }
+
+ if (k->get_vhost) {
+ struct vhost_dev *hdev = k->get_vhost(vdev);
+ /* Only reset when vhost back-end is connected */
+ if (hdev && hdev->vhost_ops) {
+ vhost_reset_device(hdev);
+ }
+ }
+
+ if (k->reset) {
+ k->reset(vdev);
+ }
+
+ vdev->start_on_kick = false;
+ vdev->started = false;
+ vdev->broken = false;
+ virtio_set_features_nocheck(vdev, 0);
+ vdev->queue_sel = 0;
+ vdev->status = 0;
+ vdev->disabled = false;
+ qatomic_set(&vdev->isr, 0);
+ vdev->config_vector = VIRTIO_NO_VECTOR;
+ virtio_notify_vector(vdev, vdev->config_vector);
+
+ for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+ __virtio_queue_reset(vdev, i);
+ }
+}
+
static void virtio_device_check_notification_compatibility(VirtIODevice
*vdev,
Error **errp)
{
---
base-commit: 825b96dbcee23d134b691fc75618b59c5f53da32
change-id: 20250406-reset-5ed5248ee3c1
Best regards,
--
Akihiko Odaki <akihiko.od...@daynix.com>
