kernel/linux.git/drivers/vhost/vhost.h, branch v6.12.80

vhost: Reintroduce kthread API and add mode selection

2025-08-15T10:13:58+00:00

[ Upstream commit 7d9896e9f6d02d8aa85e63f736871f96c59a5263 ] Since commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads"), the vhost uses vhost_task and operates as a child of the owner thread. This is required for correct CPU usage accounting, especially when using containers. However, this change has caused confusion for some legacy userspace applications, and we didn't notice until it's too late. Unfortunately, it's too late to revert - we now have userspace depending both on old and new behaviour :( To address the issue, reintroduce kthread mode for vhost workers and provide a configuration to select between kthread and task worker. - Add 'fork_owner' parameter to vhost_dev to let users select kthread or task mode. Default mode is task mode(VHOST_FORK_OWNER_TASK). - Reintroduce kthread mode support: * Bring back the original vhost_worker() implementation, and renamed to vhost_run_work_kthread_list(). * Add cgroup support for the kthread * Introduce struct vhost_worker_ops: - Encapsulates create / stop / wake‑up callbacks. - vhost_worker_create() selects the proper ops according to inherit_owner. - Userspace configuration interface: * New IOCTLs: - VHOST_SET_FORK_FROM_OWNER lets userspace select task mode (VHOST_FORK_OWNER_TASK) or kthread mode (VHOST_FORK_OWNER_KTHREAD) - VHOST_GET_FORK_FROM_OWNER reads the current worker mode * Expose module parameter 'fork_from_owner_default' to allow system administrators to configure the default mode for vhost workers * Kconfig option CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL controls whether these IOCTLs and the parameter are available - The VHOST_NEW_WORKER functionality requires fork_owner to be set to true, with validation added to ensure proper configuration This partially reverts or improves upon: commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads") commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray") Fixes: 6e890c5d5021 ("vhost: use vhost_tasks for worker threads"), Signed-off-by: Cindy Lu Message-Id: <20250714071333.59794-2-lulu@redhat.com> Signed-off-by: Michael S. Tsirkin Acked-by: Jason Wang Tested-by: Lei Yang Signed-off-by: Sasha Levin

vhost_task: Handle SIGKILL by flushing work and exiting

2024-05-22T12:31:15+00:00

Instead of lingering until the device is closed, this has us handle SIGKILL by: 1. marking the worker as killed so we no longer try to use it with new virtqueues and new flush operations. 2. setting the virtqueue to worker mapping so no new works are queued. 3. running all the exiting works. Suggested-by: Edward Adam Davis Reported-and-tested-by: syzbot+98edc2df894917b3431f@syzkaller.appspotmail.com Message-Id: Signed-off-by: Mike Christie Message-Id: <20240316004707.45557-9-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

vhost: Remove vhost_vq_flush

2024-05-22T12:31:15+00:00

vhost_vq_flush is no longer used so remove it. Signed-off-by: Mike Christie Message-Id: <20240316004707.45557-5-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

eventfd: simplify eventfd_signal()

2023-11-28T13:08:38+00:00

Ever since the eventfd type was introduced back in 2007 in commit e1ad7468c77d ("signal/timer/event: eventfd core") the eventfd_signal() function only ever passed 1 as a value for @n. There's no point in keeping that additional argument. Link: https://lore.kernel.org/r/20231122-vfs-eventfd-signal-v2-2-bd549b14ce0c@kernel.org Acked-by: Xu Yilun Acked-by: Andrew Donnellan # ocxl Acked-by: Eric Farman # s390 Reviewed-by: Jan Kara Reviewed-by: Jens Axboe Signed-off-by: Christian Brauner

vhost: Make parameter name match of vhost_get_vq_desc()

2023-07-03T16:15:15+00:00

The parameter name in the function declaration and definition should be the same. drivers/vhost/vhost.h, int vhost_get_vq_desc(..., unsigned int iov_count,...); drivers/vhost/vhost.c, int vhost_get_vq_desc(..., unsigned int iov_size,...) Signed-off-by: Xianting Tian Message-Id: <20230621093835.36878-1-xianting.tian@linux.alibaba.com> Signed-off-by: Michael S. Tsirkin

vhost: Allow worker switching while work is queueing

2023-07-03T16:15:14+00:00

This patch drops the requirement that we can only switch workers if work has not been queued by using RCU for the vq based queueing paths and a mutex for the device wide flush. We can also use this to support SIGKILL properly in the future where we should exit almost immediately after getting that signal. With this patch, when get_signal returns true, we can set the vq->worker to NULL and do a synchronize_rcu to prevent new work from being queued to the vhost_task that has been killed. Signed-off-by: Mike Christie Message-Id: <20230626232307.97930-18-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

vhost: allow userspace to create workers

2023-07-03T16:15:14+00:00

For vhost-scsi with 3 vqs or more and a workload that tries to use them in parallel like: fio --filename=/dev/sdb --direct=1 --rw=randrw --bs=4k \ --ioengine=libaio --iodepth=128 --numjobs=3 the single vhost worker thread will become a bottlneck and we are stuck at around 500K IOPs no matter how many jobs, virtqueues, and CPUs are used. To better utilize virtqueues and available CPUs, this patch allows userspace to create workers and bind them to vqs. You can have N workers per dev and also share N workers with M vqs on that dev. This patch adds the interface related code and the next patch will hook vhost-scsi into it. The patches do not try to hook net and vsock into the interface because: 1. multiple workers don't seem to help vsock. The problem is that with only 2 virtqueues we never fully use the existing worker when doing bidirectional tests. This seems to match vhost-scsi where we don't see the worker as a bottleneck until 3 virtqueues are used. 2. net already has a way to use multiple workers. Signed-off-by: Mike Christie Message-Id: <20230626232307.97930-16-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

vhost: replace single worker pointer with xarray

2023-07-03T16:15:14+00:00

The next patch allows userspace to create multiple workers per device, so this patch replaces the vhost_worker pointer with an xarray so we can store mupltiple workers and look them up. Signed-off-by: Mike Christie Message-Id: <20230626232307.97930-15-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

vhost: remove vhost_work_queue

2023-07-03T16:15:14+00:00

vhost_work_queue is no longer used. Each driver is using the poll or vq based queueing, so remove vhost_work_queue. Signed-off-by: Mike Christie Message-Id: <20230626232307.97930-13-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin

vhost: convert poll work to be vq based

2023-07-03T16:15:13+00:00

This has the drivers pass in their poll to vq mapping and then converts the core poll code to use the vq based helpers. In the next patches we will allow vqs to be handled by different workers, so to allow drivers to execute operations like queue, stop, flush, etc on specific polls/vqs we need to know the mappings. Signed-off-by: Mike Christie Message-Id: <20230626232307.97930-8-michael.christie@oracle.com> Signed-off-by: Michael S. Tsirkin