On Mon, Mar 4, 2024 at 6:09 PM Jonah Palmer <jonah.pal...@oracle.com> wrote:
>
>
>
> On 3/1/24 2:31 PM, Eugenio Perez Martin wrote:
> > On Fri, Mar 1, 2024 at 2:44 PM Jonah Palmer <jonah.pal...@oracle.com> wrote:
> >>
> >> Add support to virtio-pci devices for handling the extra data sent
> >> from the driver to the device when the VIRTIO_F_NOTIFICATION_DATA
> >> transport feature has been negotiated.
> >>
> >> The extra data that's passed to the virtio-pci device when this
> >> feature is enabled varies depending on the device's virtqueue
> >> layout.
> >>
> >> In a split virtqueue layout, this data includes:
> >> - upper 16 bits: last_avail_idx
> >> - lower 16 bits: virtqueue index
> >>
> >> In a packed virtqueue layout, this data includes:
> >> - upper 16 bits: 1-bit wrap counter & 15-bit last_avail_idx
> >> - lower 16 bits: virtqueue index
> >>
> >> Signed-off-by: Jonah Palmer <jonah.pal...@oracle.com>
> >> ---
> >> hw/virtio/virtio-pci.c | 13 ++++++++++---
> >> hw/virtio/virtio.c | 13 +++++++++++++
> >> include/hw/virtio/virtio.h | 1 +
> >> 3 files changed, 24 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> >> index 1a7039fb0c..c7c577b177 100644
> >> --- a/hw/virtio/virtio-pci.c
> >> +++ b/hw/virtio/virtio-pci.c
> >> @@ -384,7 +384,7 @@ static void virtio_ioport_write(void *opaque, uint32_t
> >> addr, uint32_t val)
> >> {
> >> VirtIOPCIProxy *proxy = opaque;
> >> VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
> >> - uint16_t vector;
> >> + uint16_t vector, vq_idx;
> >> hwaddr pa;
> >>
> >> switch (addr) {
> >> @@ -408,8 +408,15 @@ static void virtio_ioport_write(void *opaque,
> >> uint32_t addr, uint32_t val)
> >> vdev->queue_sel = val;
> >> break;
> >> case VIRTIO_PCI_QUEUE_NOTIFY:
> >> - if (val < VIRTIO_QUEUE_MAX) {
> >> - virtio_queue_notify(vdev, val);
> >> + if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA)) {
> >> + vq_idx = val & 0xFFFF;
> >
> > Nitpick, but since vq_idx is already a uint16_t the & 0xFFFF is not
> > needed.
>
> Ah okay. I wasn't sure if it was worthwhile to keep the '& 0xFFFF' in or
> not for the sake of clarity and good practice. In that case I could just
> do away with vq_idx here and use explicit casting on 'val'.
>
> > I think it's cleaner just to call virtio_set_notification data
> > in the has_feature(...) condition, but I'm happy with this too.
>
> Do you mean something like:
>
> if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA) &&
> virtio_set_notification_data(vdev, vq_idx, val)) {
> ...
> }
>
Sorry I was not clear, I meant just to take out the common code of the
conditionals:
vq_idx = val;
if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA) {
virtio_set_notification_data(vdev, val);
}
> Though I'm not sure what would then go in the body of this conditional,
> especially if I did something like:
>
> case VIRTIO_PCI_QUEUE_NOTIFY:
> if ((uint16_t)val < VIRTIO_QUEUE_MAX) {
> if (virtio_vdev_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA) &&
> virtio_set_notification_data(vdev, val)) {
> // Not sure what to put here other than a no-op
> }
>
> virtio_queue_notify(vdev, (uint16_t)val);
> }
> break;
>
> But I'm not sure if you'd prefer this explicit casting of 'val' over
> implicit casting like:
>
> uint16_t vq_idx = val;
>
> >
> >> + virtio_set_notification_data(vdev, vq_idx, val);
> >> + } else {
> >> + vq_idx = val;
> >> + }
> >> +
> >> + if (vq_idx < VIRTIO_QUEUE_MAX) {
> >> + virtio_queue_notify(vdev, vq_idx);
> >> }
> >> break;
> >> case VIRTIO_PCI_STATUS:
> >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >> index d229755eae..a61f69b7fd 100644
> >> --- a/hw/virtio/virtio.c
> >> +++ b/hw/virtio/virtio.c
> >> @@ -2052,6 +2052,19 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t
> >> val)
> >> return 0;
> >> }
> >>
> >> +void virtio_set_notification_data(VirtIODevice *vdev, uint16_t i,
> >> uint32_t data)
> >> +{
> >> + VirtQueue *vq = &vdev->vq[i];
> >> +
> >> + if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >> + vq->last_avail_wrap_counter = (data >> 31) & 0x1;
> >> + vq->last_avail_idx = (data >> 16) & 0x7FFF;
> >> + } else {
> >> + vq->last_avail_idx = (data >> 16) & 0xFFFF;
> >> + }
> >
> > It should not set last_avail_idx, only shadow_avail_idx. Otherwise,
> > QEMU can only see the descriptors placed after the notification.
> >
> > Or am I missing something?
> >
> > In that regard, I would call this function
> > "virtqueue_set_shadow_avail_idx". But I'm very bad at naming :).
>
> Ah that's right. This would make Qemu skip processing descriptors that
> might've been made available before the notification but after the
> host's last check of last_avail_idx. In other words, ignoring available
> descriptors that were placed before the notification but not yet
> processed. Good catch, thank you!
>
> So, for the packed VQ layout, we'll still want to save the wrap counter
> but for the shadow_avail_idx, right? E.g.
>
> if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> vq->shadow_avail_wrap_counter = (data >> 31) & 0x1;
> vq->shadow_avail_idx = (data >> 16) & 0x7FFF;
> } else {
> vq->shadow_avail_idx = (data >> 16);
> }
>
Right, I was not clear enough again :). You probably have guessed
already but not modifying avail_wrap_counter would make QEMu to read
the wrong index too.
Thanks!
> >
> > The rest looks good to me.
> >
> > Thanks!
> >
> >> + vq->shadow_avail_idx = vq->last_avail_idx;
> >> +}
> >> +
> >> static enum virtio_device_endian virtio_default_endian(void)
> >> {
> >> if (target_words_bigendian()) {
> >> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> >> index c8f72850bc..c92d8afc42 100644
> >> --- a/include/hw/virtio/virtio.h
> >> +++ b/include/hw/virtio/virtio.h
> >> @@ -345,6 +345,7 @@ void virtio_queue_reset(VirtIODevice *vdev, uint32_t
> >> queue_index);
> >> void virtio_queue_enable(VirtIODevice *vdev, uint32_t queue_index);
> >> void virtio_update_irq(VirtIODevice *vdev);
> >> int virtio_set_features(VirtIODevice *vdev, uint64_t val);
> >> +void virtio_set_notification_data(VirtIODevice *vdev, uint16_t i,
> >> uint32_t data);
> >>
> >> /* Base devices. */
> >> typedef struct VirtIOBlkConf VirtIOBlkConf;
> >> --
> >> 2.39.3
> >>
> >
>
