On Thu, Jul 23, 2026 at 03:30:08PM -0700, Connor Kite wrote: > By default svq vrings are placed in an anonymous memory map. As svqs > will be leveraged to enable memory isolation in vhost-user, it is useful > to be able to place the vrings in a shared isolation memory region. > > Adds the option to specify vring placement by providing a vring base > address before starting the svq. > > Signed-off-by: Connor Kite <[email protected]> > --- > hw/virtio/vhost-shadow-virtqueue.c | 22 +++++++++++++++------- > hw/virtio/vhost-shadow-virtqueue.h | 3 +++ > 2 files changed, 18 insertions(+), 7 deletions(-) > > diff --git a/hw/virtio/vhost-shadow-virtqueue.c > b/hw/virtio/vhost-shadow-virtqueue.c > index eb86c1ee37..9e3c359f50 100644 > --- a/hw/virtio/vhost-shadow-virtqueue.c > +++ b/hw/virtio/vhost-shadow-virtqueue.c > @@ -857,14 +857,21 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, > VirtIODevice *vdev, > > svq->vring.num = virtio_queue_get_num(vdev, virtio_get_queue_index(vq)); > svq->num_free = svq->vring.num; > - svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq), > - PROT_READ | PROT_WRITE, MAP_SHARED | > MAP_ANONYMOUS, > - -1, 0); > desc_size = sizeof(vring_desc_t) * svq->vring.num; > - svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); > - svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq), > - PROT_READ | PROT_WRITE, MAP_SHARED | > MAP_ANONYMOUS, > - -1, 0); > + if (svq->base_addr == NULL) { > + svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq), > + PROT_READ | PROT_WRITE, MAP_SHARED | > MAP_ANONYMOUS, > + -1, 0); > + svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); > + svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq), > + PROT_READ | PROT_WRITE, MAP_SHARED | > MAP_ANONYMOUS, > + -1, 0); > + } else { > + svq->vring.desc = (void *) svq->base_addr; > + svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); > + svq->vring.used = (void *)((char *)svq->base_addr + > + vhost_svq_driver_area_size(svq)); > + } > svq->desc_state = g_new0(SVQDescState, svq->vring.num); > if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_IN_ORDER)) { > svq->batch_last.id = VIRTIO_RING_NOT_IN_BATCH; > @@ -929,6 +936,7 @@ VhostShadowVirtqueue *vhost_svq_new(const > VhostShadowVirtqueueOps *ops, > event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND); > svq->ops = ops; > svq->ops_opaque = ops_opaque; > + svq->base_addr = NULL; > return svq; > } > > diff --git a/hw/virtio/vhost-shadow-virtqueue.h > b/hw/virtio/vhost-shadow-virtqueue.h > index ccfeee36d7..39f69e6455 100644 > --- a/hw/virtio/vhost-shadow-virtqueue.h > +++ b/hw/virtio/vhost-shadow-virtqueue.h > @@ -148,6 +148,9 @@ typedef struct VhostShadowVirtqueue { > > /* Size of SVQ vring free descriptors */ > uint16_t num_free; > + > + /* Location assigned to vrings if not in default anon memory map*/ > + hwaddr *base_addr;
Why is base_addr a hwaddr? This is QEMU memory, not guest RAM. I expected this to be void *. A size needs to be at least documented here to reduce the chance of memory bugs. Even better would be an interface like vhost_svq_vring_total_size() so the caller can fetch the number of bytes before allocating the memory.
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