Reviewed-by: Raphael Norwitz <raphael.s.norwitz@gmail.com>
On Wed, Aug 13, 2025 at 12:56 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
> hw/virtio/vhost.c | 71 ++++++++++++++++++++++++++---------------------
> 1 file changed, 40 insertions(+), 31 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index a8f8b85012..f9163ba895 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1553,11 +1553,49 @@ static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
> }
> }
>
> +static bool check_memslots(struct vhost_dev *hdev, Error **errp)
> +{
> + unsigned int used, reserved, limit;
> +
> + limit = hdev->vhost_ops->vhost_backend_memslots_limit(hdev);
> + if (limit < MEMORY_DEVICES_SAFE_MAX_MEMSLOTS &&
> + memory_devices_memslot_auto_decision_active()) {
> + error_setg(errp, "some memory device (like virtio-mem)"
> + " decided how many memory slots to use based on the overall"
> + " number of memory slots; this vhost backend would further"
> + " restricts the overall number of memory slots");
> + error_append_hint(errp, "Try plugging this vhost backend before"
> + " plugging such memory devices.\n");
> + return false;
> + }
> +
> + /*
> + * The listener we registered properly setup the number of required
> + * memslots in vhost_commit().
> + */
> + used = hdev->mem->nregions;
> +
> + /*
> + * We assume that all reserved memslots actually require a real memslot
> + * in our vhost backend. This might not be true, for example, if the
> + * memslot would be ROM. If ever relevant, we can optimize for that --
> + * but we'll need additional information about the reservations.
> + */
> + reserved = memory_devices_get_reserved_memslots();
> + if (used + reserved > limit) {
> + error_setg(errp, "vhost backend memory slots limit (%d) is less"
> + " than current number of used (%d) and reserved (%d)"
> + " memory slots for memory devices.", limit, used, reserved);
> + return false;
> + }
> +
> + return true;
> +}
> +
> int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> VhostBackendType backend_type, uint32_t busyloop_timeout,
> Error **errp)
> {
> - unsigned int used, reserved, limit;
> uint64_t features;
> int i, r, n_initialized_vqs = 0;
>
> @@ -1584,19 +1622,6 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> goto fail;
> }
>
> - limit = hdev->vhost_ops->vhost_backend_memslots_limit(hdev);
> - if (limit < MEMORY_DEVICES_SAFE_MAX_MEMSLOTS &&
> - memory_devices_memslot_auto_decision_active()) {
> - error_setg(errp, "some memory device (like virtio-mem)"
> - " decided how many memory slots to use based on the overall"
> - " number of memory slots; this vhost backend would further"
> - " restricts the overall number of memory slots");
> - error_append_hint(errp, "Try plugging this vhost backend before"
> - " plugging such memory devices.\n");
> - r = -EINVAL;
> - goto fail;
> - }
> -
> for (i = 0; i < hdev->nvqs; ++i, ++n_initialized_vqs) {
> r = vhost_virtqueue_init(hdev, hdev->vqs + i, hdev->vq_index + i,
> busyloop_timeout);
> @@ -1655,23 +1680,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> memory_listener_register(&hdev->memory_listener, &address_space_memory);
> QLIST_INSERT_HEAD(&vhost_devices, hdev, entry);
>
> - /*
> - * The listener we registered properly setup the number of required
> - * memslots in vhost_commit().
> - */
> - used = hdev->mem->nregions;
> -
> - /*
> - * We assume that all reserved memslots actually require a real memslot
> - * in our vhost backend. This might not be true, for example, if the
> - * memslot would be ROM. If ever relevant, we can optimize for that --
> - * but we'll need additional information about the reservations.
> - */
> - reserved = memory_devices_get_reserved_memslots();
> - if (used + reserved > limit) {
> - error_setg(errp, "vhost backend memory slots limit (%d) is less"
> - " than current number of used (%d) and reserved (%d)"
> - " memory slots for memory devices.", limit, used, reserved);
> + if (!check_memslots(hdev, errp)) {
> r = -EINVAL;
> goto fail;
> }
> --
> 2.48.1
>
>