On Wed, Oct 15, 2025 at 05:58:02PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
> Reviewed-by: Raphael Norwitz <[email protected]>
> Reviewed-by: Daniil Tatianin <[email protected]>
This needs a better commit log.
the subject makes it look like it's merely adding a helper
but it is not the case: e.g. errors are now handled
somewhat differently.
Pls document the thinking process explaining why it does not
matter. CB.
> ---
> 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 34846edf36..56a812b06b 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1572,12 +1572,50 @@ static int vhost_dev_get_features(struct vhost_dev
> *hdev,
> return r;
> }
>
> +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
This comment worked in the original code but not now.
The listener here is memory_listener_register which yes happens to
be called before check_memslots but it is far from obvious.
> + * 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)
> {
> uint64_t features[VIRTIO_FEATURES_NU64S];
> - unsigned int used, reserved, limit;
> int i, r, n_initialized_vqs = 0;
>
> hdev->vdev = NULL;
> @@ -1603,19 +1641,6 @@ 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);
> @@ -1674,23 +1699,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void
> *opaque,
> memory_listener_register(&hdev->memory_listener, &address_space_memory);
So it looks like with your change
this will temporarily register the listener
restricting the number of slots, then check and unregister.
Is this ever a problem?
commit log needs better documentation why.
> 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
