drivers/virt/acrn/irqfd.c

// SPDX-License-Identifier: GPL-2.0
/*
 * ACRN HSM irqfd: use eventfd objects to inject virtual interrupts
 *
 * Copyright (C) 2020 Intel Corporation. All rights reserved.
 *
 * Authors:
 *	Shuo Liu <shuo.a.liu@intel.com>
 *	Yakui Zhao <yakui.zhao@intel.com>
 */

#include <linux/eventfd.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>

#include "acrn_drv.h"

/* Cleanup work has been queued; set via test_and_set_bit(). */
#define HSM_IRQFD_FLAG_SHUTDOWN	0

/**
 * struct hsm_irqfd - Properties of HSM irqfd
 * @vm:		Associated VM pointer
 * @wait:	Entry of wait-queue
 * @shutdown:	Async shutdown work
 * @eventfd:	Associated eventfd
 * @list:	Entry within &acrn_vm.irqfds of irqfds of a VM
 * @pt:		Structure for select/poll on the associated eventfd
 * @msi:	MSI data
 * @flags:	Internal lifecycle flags (HSM_IRQFD_FLAG_*)
 */
struct hsm_irqfd {
	struct acrn_vm		*vm;
	wait_queue_entry_t	wait;
	struct work_struct	shutdown;
	struct eventfd_ctx	*eventfd;
	struct list_head	list;
	poll_table		pt;
	struct acrn_msi_entry	msi;
	unsigned long		flags;
};

static void acrn_irqfd_inject(struct hsm_irqfd *irqfd)
{
	struct acrn_vm *vm = irqfd->vm;

	acrn_msi_inject(vm, irqfd->msi.msi_addr,
			irqfd->msi.msi_data);
}

/* Queue the cleanup work at most once. Safe from atomic context. */
static void hsm_irqfd_queue_shutdown(struct hsm_irqfd *irqfd)
{
	if (!test_and_set_bit(HSM_IRQFD_FLAG_SHUTDOWN, &irqfd->flags))
		queue_work(irqfd->vm->irqfd_wq, &irqfd->shutdown);
}

/* Sole owner of @irqfd: unhook waitqueue, drop eventfd ref, free. */
static void hsm_irqfd_shutdown_work(struct work_struct *work)
{
	struct hsm_irqfd *irqfd = container_of(work, struct hsm_irqfd,
					       shutdown);
	struct acrn_vm *vm = irqfd->vm;
	u64 cnt;

	mutex_lock(&vm->irqfds_lock);
	if (!list_empty(&irqfd->list))
		list_del_init(&irqfd->list);
	mutex_unlock(&vm->irqfds_lock);

	eventfd_ctx_remove_wait_queue(irqfd->eventfd, &irqfd->wait, &cnt);
	eventfd_ctx_put(irqfd->eventfd);
	kfree(irqfd);
}

/* Called with wqh->lock held and interrupts disabled */
static int hsm_irqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode,
			    int sync, void *key)
{
	unsigned long poll_bits = (unsigned long)key;
	struct hsm_irqfd *irqfd;

	irqfd = container_of(wait, struct hsm_irqfd, wait);

	if (poll_bits & POLLIN)
		/* An event has been signaled, inject an interrupt */
		acrn_irqfd_inject(irqfd);

	if (poll_bits & POLLHUP)
		/* Defer teardown to the cleanup work; can't sleep here. */
		hsm_irqfd_queue_shutdown(irqfd);

	return 0;
}

static void hsm_irqfd_poll_func(struct file *file, wait_queue_head_t *wqh,
				poll_table *pt)
{
	struct hsm_irqfd *irqfd;

	irqfd = container_of(pt, struct hsm_irqfd, pt);
	add_wait_queue(wqh, &irqfd->wait);
}

/*
 * Assign an eventfd to a VM and create a HSM irqfd associated with the
 * eventfd. The properties of the HSM irqfd are built from a &struct
 * acrn_irqfd.
 */
static int acrn_irqfd_assign(struct acrn_vm *vm, struct acrn_irqfd *args)
{
	struct eventfd_ctx *eventfd = NULL;
	struct hsm_irqfd *irqfd, *tmp;
	__poll_t events;
	int ret = 0;

	irqfd = kzalloc_obj(*irqfd);
	if (!irqfd)
		return -ENOMEM;

	irqfd->vm = vm;
	memcpy(&irqfd->msi, &args->msi, sizeof(args->msi));
	INIT_LIST_HEAD(&irqfd->list);
	INIT_WORK(&irqfd->shutdown, hsm_irqfd_shutdown_work);

	CLASS(fd, f)(args->fd);
	if (fd_empty(f)) {
		ret = -EBADF;
		goto out;
	}

	eventfd = eventfd_ctx_fileget(fd_file(f));
	if (IS_ERR(eventfd)) {
		ret = PTR_ERR(eventfd);
		goto out;
	}

	irqfd->eventfd = eventfd;

	/*
	 * Install custom wake-up handling to be notified whenever underlying
	 * eventfd is signaled.
	 */
	init_waitqueue_func_entry(&irqfd->wait, hsm_irqfd_wakeup);
	init_poll_funcptr(&irqfd->pt, hsm_irqfd_poll_func);

	/*
	 * Hold irqfds_lock across waitqueue install and list_add so the
	 * irqfd is not visible to deassign/deinit before its waitqueue
	 * entry is in place, and any racing EPOLLHUP cleanup work blocks
	 * on irqfds_lock until publication completes.
	 */
	mutex_lock(&vm->irqfds_lock);
	list_for_each_entry(tmp, &vm->irqfds, list) {
		if (irqfd->eventfd != tmp->eventfd)
			continue;
		ret = -EBUSY;
		mutex_unlock(&vm->irqfds_lock);
		goto fail;
	}

	events = vfs_poll(fd_file(f), &irqfd->pt);
	list_add_tail(&irqfd->list, &vm->irqfds);
	if (events & EPOLLIN)
		acrn_irqfd_inject(irqfd);
	mutex_unlock(&vm->irqfds_lock);

	return 0;
fail:
	eventfd_ctx_put(eventfd);
out:
	kfree(irqfd);
	return ret;
}

static int acrn_irqfd_deassign(struct acrn_vm *vm,
			       struct acrn_irqfd *args)
{
	struct hsm_irqfd *irqfd, *tmp;
	struct eventfd_ctx *eventfd;

	eventfd = eventfd_ctx_fdget(args->fd);
	if (IS_ERR(eventfd))
		return PTR_ERR(eventfd);

	mutex_lock(&vm->irqfds_lock);
	list_for_each_entry_safe(irqfd, tmp, &vm->irqfds, list) {
		if (irqfd->eventfd == eventfd) {
			list_del_init(&irqfd->list);
			hsm_irqfd_queue_shutdown(irqfd);
			break;
		}
	}
	mutex_unlock(&vm->irqfds_lock);
	eventfd_ctx_put(eventfd);

	/* Wait for cleanup work to finish so the eventfd is fully detached. */
	flush_workqueue(vm->irqfd_wq);

	return 0;
}

int acrn_irqfd_config(struct acrn_vm *vm, struct acrn_irqfd *args)
{
	int ret;

	if (args->flags & ACRN_IRQFD_FLAG_DEASSIGN)
		ret = acrn_irqfd_deassign(vm, args);
	else
		ret = acrn_irqfd_assign(vm, args);

	return ret;
}

int acrn_irqfd_init(struct acrn_vm *vm)
{
	INIT_LIST_HEAD(&vm->irqfds);
	mutex_init(&vm->irqfds_lock);
	vm->irqfd_wq = alloc_workqueue("acrn_irqfd-%u", WQ_PERCPU, 0, vm->vmid);
	if (!vm->irqfd_wq)
		return -ENOMEM;

	dev_dbg(acrn_dev.this_device, "VM %u irqfd init.\n", vm->vmid);
	return 0;
}

void acrn_irqfd_deinit(struct acrn_vm *vm)
{
	struct hsm_irqfd *irqfd, *next;

	dev_dbg(acrn_dev.this_device, "VM %u irqfd deinit.\n", vm->vmid);

	mutex_lock(&vm->irqfds_lock);
	list_for_each_entry_safe(irqfd, next, &vm->irqfds, list) {
		list_del_init(&irqfd->list);
		hsm_irqfd_queue_shutdown(irqfd);
	}
	mutex_unlock(&vm->irqfds_lock);

	/* Drain all cleanup work before tearing the workqueue down. */
	flush_workqueue(vm->irqfd_wq);
	destroy_workqueue(vm->irqfd_wq);
}