Re: [PATCH RFC 09/15] hw/virtio/vhost-shadow-virtqueue: specified vring placement

--Dl4fy5/Nk4W7j/qR
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

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.
>=20
> Adds the option to specify vring placement by providing a vring base
> address before starting the svq.
>=20
> 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(-)
>=20
> 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, Vir=
tIODevice *vdev,
> =20
>      svq->vring.num =3D virtio_queue_get_num(vdev, virtio_get_queue_index=
(vq));
>      svq->num_free =3D svq->vring.num;
> -    svq->vring.desc =3D mmap(NULL, vhost_svq_driver_area_size(svq),
> -                           PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON=
YMOUS,
> -                           -1, 0);
>      desc_size =3D sizeof(vring_desc_t) * svq->vring.num;
> -    svq->vring.avail =3D (void *)((char *)svq->vring.desc + desc_size);
> -    svq->vring.used =3D mmap(NULL, vhost_svq_device_area_size(svq),
> -                           PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON=
YMOUS,
> -                           -1, 0);
> +    if (svq->base_addr =3D=3D NULL) {
> +        svq->vring.desc =3D mmap(NULL, vhost_svq_driver_area_size(svq),
> +                            PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANO=
NYMOUS,
> +                            -1, 0);
> +        svq->vring.avail =3D (void *)((char *)svq->vring.desc + desc_siz=
e);
> +        svq->vring.used =3D mmap(NULL, vhost_svq_device_area_size(svq),
> +                            PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANO=
NYMOUS,
> +                            -1, 0);
> +    } else {
> +        svq->vring.desc =3D (void *) svq->base_addr;
> +        svq->vring.avail =3D (void *)((char *)svq->vring.desc + desc_siz=
e);
> +        svq->vring.used =3D (void *)((char *)svq->base_addr +
> +                          vhost_svq_driver_area_size(svq));
> +    }
>      svq->desc_state =3D g_new0(SVQDescState, svq->vring.num);
>      if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_IN_ORDER)) {
>          svq->batch_last.id =3D VIRTIO_RING_NOT_IN_BATCH;
> @@ -929,6 +936,7 @@ VhostShadowVirtqueue *vhost_svq_new(const VhostShadow=
VirtqueueOps *ops,
>      event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
>      svq->ops =3D ops;
>      svq->ops_opaque =3D ops_opaque;
> +    svq->base_addr =3D NULL;
>      return svq;
>  }
> =20
> 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 {
> =20
>      /* 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.

--Dl4fy5/Nk4W7j/qR
Content-Type: application/pgp-signature; name=signature.asc

-----BEGIN PGP SIGNATURE-----

iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmpoyVwACgkQnKSrs4Gr
c8jUuwgAvMc/G3tOhj0RTFEXylyhHMcyDAfcvVg+19MNnwq8RSuEjpwK7ongL+Do
s3rzWOVKWxQS8RMFhq0E1zXoLWZ0+nt3Ziqi2XBOj28SEiO3eZyfXMQ6lC1UYo1i
ZiN0+qHov/H69XAb8cKJgt4xKyiLhVEZfC/DKBzNzVOiFHApRfzdPQapfqTXA4PJ
5z0v+rRysNK9dCaLDf6hqlXki1xWm3M877IeDEztVtof0FolUwLgy4DM9r8lwEdi
efKoa9g6Jb083QGMMCKEzXR5wkxvrIVsbIc/OonhN8XDNjJNPpiaZeLlDj0WddGb
BECKOD1lZ+YB9/soytLlda2bjV2M8g==
=jc6J
-----END PGP SIGNATURE-----

--Dl4fy5/Nk4W7j/qR--