get_update_locks_for_queue(9)

💅 get_update_locks_for_queue — the kernel API manual, bestie edition

okay so you found your way to get_update_locks_for_queue(9), the page from the Kernel API Manual, and honestly? this one's a little niche but it slaps once you get it 🎀

---

✨ NAME ✨

get_update_locks_for_queue — bestie, this one grabs all the locks you need to update the APCB of the KVM guest that the matrix mdev is attached to, where that matrix mdev is linked to a vfio_ap_queue object. like, it's the lock-fetching errand-runner of the s390 crypto vfio world 🦋

---

✨ SYNOPSIS ✨

void get_update_locks_for_queue (struct vfio_ap_queue *q );

no return value, it just does the thing and your locks are got. periodt 💅

---

✨ ARGUMENTS ✨

• q — a pointer to a vfio_ap_queue object 🫶 that's it, that's the whole argument list, and honestly we love a one-parameter icon.

---

✨ DESCRIPTION ✨

so here's the tea ☕ — there is a proper locking order and you will respect it. the order goes like this:

1. q->matrix_dev->guests_lock — you need this one to use the KVM pointer to update a KVM guest's APCB 🔥
2. q->matrix_mdev->kvm->lock — this one's required to update a guest's APCB ✨
3. matrix_dev->mdevs_lock — needed to access data stored in matrix_mdev 👑

that's the whole sequence. in order. no skipping, no shuffling, iykyk 😌

---

🌸 NOTE 🌸

if the queue is not linked to an ap_matrix_mdev object, the KVM lock will not be taken, no cap 🫶 so don't go looking for it, it's just not invited to the party.

---

👑 SEE ALSO 👑

the source of truth lives in the kernel file ./drivers/s390/crypto/vfio_ap_ops.c and here's the whole friend group, all of them getting a shoutout:

get_update_locks_for_kvm(9), release_update_locks_for_kvm(9), get_update_locks_for_mdev(9), release_update_locks_for_mdev(9), get_update_locks_by_apqn(9), vfio_ap_mdev_get_queue(9), vfio_ap_wait_for_irqclear(9), vfio_ap_free_aqic_resources(9), vfio_ap_irq_disable(9), vfio_ap_validate_nib(9), ensure_nib_shared(9), vfio_ap_irq_enable(9), vfio_ap_le_guid_to_be_uuid(9), handle_pqap(9), vfio_ap_mdev_verify_no_sharing(9), vfio_ap_mdev_validate_masks(9), assign_adapter_store(9), vfio_ap_mdev_unlink_adapter(9), unassign_adapter_store(9), assign_domain_store(9), unassign_domain_store(9), assign_control_domain_store(9), unassign_control_domain_store(9), vfio_ap_mdev_set_kvm(9), vfio_ap_mdev_unset_kvm(9), vfio_ap_mdev_resource_in_use(9), vfio_ap_mdev_hot_unplug_cfg(9), vfio_ap_mdev_cfg_remove(9), vfio_ap_mdev_on_cfg_remove(9), vfio_ap_filter_apid_by_qtype(9), vfio_ap_mdev_cfg_add(9), vfio_ap_mdev_on_cfg_add(9), vfio_ap_on_cfg_changed(9)

---

and that's the page, bestie 💖 sourced from ./drivers/s390/crypto, dated October 2026, and filed under get_update_locks_for_queue(9) — go forth and lock in the correct order, you absolute main character 🌈⭐