text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (C) 2017 - Cambridge Greys Ltd
   * Copyright (C) 2011 - 2014 Cisco Systems Inc
   * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
   *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
   */
  
  #include <linux/cpumask.h>
  #include <linux/hardirq.h>
  #include <linux/interrupt.h>
  #include <linux/kernel_stat.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/seq_file.h>
  #include <linux/slab.h>
  #include <as-layout.h>
  #include <kern_util.h>
  #include <os.h>
  #include <irq_user.h>
  
  
  extern void free_irqs(void);
  
  /* When epoll triggers we do not know why it did so
   * we can also have different IRQs for read and write.
   * This is why we keep a small irq_fd array for each fd -
   * one entry per IRQ type
   */
  
  struct irq_entry {
  	struct irq_entry *next;
  	int fd;
  	struct irq_fd *irq_array[MAX_IRQ_TYPE + 1];
  };
  
  static struct irq_entry *active_fds;
  
  static DEFINE_SPINLOCK(irq_lock);
  
  static void irq_io_loop(struct irq_fd *irq, struct uml_pt_regs *regs)
  {
  /*
   * irq->active guards against reentry
   * irq->pending accumulates pending requests
   * if pending is raised the irq_handler is re-run
   * until pending is cleared
   */
  	if (irq->active) {
  		irq->active = false;
  		do {
  			irq->pending = false;
  			do_IRQ(irq->irq, regs);
  		} while (irq->pending && (!irq->purge));
  		if (!irq->purge)
  			irq->active = true;
  	} else {
  		irq->pending = true;
  	}
  }
  
  void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
  {
  	struct irq_entry *irq_entry;
  	struct irq_fd *irq;
  
  	int n, i, j;
  
  	while (1) {
  		/* This is now lockless - epoll keeps back-referencesto the irqs
  		 * which have trigger it so there is no need to walk the irq
  		 * list and lock it every time. We avoid locking by turning off
  		 * IO for a specific fd by executing os_del_epoll_fd(fd) before
  		 * we do any changes to the actual data structures
  		 */
  		n = os_waiting_for_events_epoll();
  
  		if (n <= 0) {
  			if (n == -EINTR)
  				continue;
  			else
  				break;
  		}
  
  		for (i = 0; i < n ; i++) {
  			/* Epoll back reference is the entry with 3 irq_fd
  			 * leaves - one for each irq type.
  			 */
  			irq_entry = (struct irq_entry *)
  				os_epoll_get_data_pointer(i);
  			for (j = 0; j < MAX_IRQ_TYPE ; j++) {
  				irq = irq_entry->irq_array[j];
  				if (irq == NULL)
  					continue;
  				if (os_epoll_triggered(i, irq->events) > 0)
  					irq_io_loop(irq, regs);
  				if (irq->purge) {
  					irq_entry->irq_array[j] = NULL;
  					kfree(irq);
  				}
  			}
  		}
  	}
  
  	free_irqs();
  }
  
  static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
  {
  	int i;
  	int events = 0;
  	struct irq_fd *irq;
  
  	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
  		irq = irq_entry->irq_array[i];
  		if (irq != NULL)
  			events = irq->events | events;
  	}
  	if (events > 0) {
  	/* os_add_epoll will call os_mod_epoll if this already exists */
  		return os_add_epoll_fd(events, irq_entry->fd, irq_entry);
  	}
  	/* No events - delete */
  	return os_del_epoll_fd(irq_entry->fd);
  }
  
  
  
  static int activate_fd(int irq, int fd, int type, void *dev_id)
  {
  	struct irq_fd *new_fd;
  	struct irq_entry *irq_entry;
  	int i, err, events;
  	unsigned long flags;
  
  	err = os_set_fd_async(fd);
  	if (err < 0)
  		goto out;
  
  	spin_lock_irqsave(&irq_lock, flags);
  
  	/* Check if we have an entry for this fd */
  
  	err = -EBUSY;
  	for (irq_entry = active_fds;
  		irq_entry != NULL; irq_entry = irq_entry->next) {
  		if (irq_entry->fd == fd)
  			break;
  	}
  
  	if (irq_entry == NULL) {
  		/* This needs to be atomic as it may be called from an
  		 * IRQ context.
  		 */
  		irq_entry = kmalloc(sizeof(struct irq_entry), GFP_ATOMIC);
  		if (irq_entry == NULL) {
  			printk(KERN_ERR
  				"Failed to allocate new IRQ entry\n");
  			goto out_unlock;
  		}
  		irq_entry->fd = fd;
  		for (i = 0; i < MAX_IRQ_TYPE; i++)
  			irq_entry->irq_array[i] = NULL;
  		irq_entry->next = active_fds;
  		active_fds = irq_entry;
  	}
  
  	/* Check if we are trying to re-register an interrupt for a
  	 * particular fd
  	 */
  
  	if (irq_entry->irq_array[type] != NULL) {
  		printk(KERN_ERR
  			"Trying to reregister IRQ %d FD %d TYPE %d ID %p\n",
  			irq, fd, type, dev_id
  		);
  		goto out_unlock;
  	} else {
  		/* New entry for this fd */
  
  		err = -ENOMEM;
  		new_fd = kmalloc(sizeof(struct irq_fd), GFP_ATOMIC);
  		if (new_fd == NULL)
  			goto out_unlock;
  
  		events = os_event_mask(type);
  
  		*new_fd = ((struct irq_fd) {
  			.id		= dev_id,
  			.irq		= irq,
  			.type		= type,
  			.events		= events,
  			.active		= true,
  			.pending	= false,
  			.purge		= false
  		});
  		/* Turn off any IO on this fd - allows us to
  		 * avoid locking the IRQ loop
  		 */
  		os_del_epoll_fd(irq_entry->fd);
  		irq_entry->irq_array[type] = new_fd;
  	}
  
  	/* Turn back IO on with the correct (new) IO event mask */
  	assign_epoll_events_to_irq(irq_entry);
  	spin_unlock_irqrestore(&irq_lock, flags);
  	maybe_sigio_broken(fd, (type != IRQ_NONE));
  
  	return 0;
  out_unlock:
  	spin_unlock_irqrestore(&irq_lock, flags);
  out:
  	return err;
  }
  
  /*
   * Walk the IRQ list and dispose of any unused entries.
   * Should be done under irq_lock.
   */
  
  static void garbage_collect_irq_entries(void)
  {
  	int i;
  	bool reap;
  	struct irq_entry *walk;
  	struct irq_entry *previous = NULL;
  	struct irq_entry *to_free;
  
  	if (active_fds == NULL)
  		return;
  	walk = active_fds;
  	while (walk != NULL) {
  		reap = true;
  		for (i = 0; i < MAX_IRQ_TYPE ; i++) {
  			if (walk->irq_array[i] != NULL) {
  				reap = false;
  				break;
  			}
  		}
  		if (reap) {
  			if (previous == NULL)
  				active_fds = walk->next;
  			else
  				previous->next = walk->next;
  			to_free = walk;
  		} else {
  			to_free = NULL;
  		}
  		walk = walk->next;
  		kfree(to_free);
  	}
  }
  
  /*
   * Walk the IRQ list and get the descriptor for our FD
   */
  
  static struct irq_entry *get_irq_entry_by_fd(int fd)
  {
  	struct irq_entry *walk = active_fds;
  
  	while (walk != NULL) {
  		if (walk->fd == fd)
  			return walk;
  		walk = walk->next;
  	}
  	return NULL;
  }
  
  
  /*
   * Walk the IRQ list and dispose of an entry for a specific
   * device, fd and number. Note - if sharing an IRQ for read
   * and writefor the same FD it will be disposed in either case.
   * If this behaviour is undesirable use different IRQ ids.
   */
  
  #define IGNORE_IRQ 1
  #define IGNORE_DEV (1<<1)
  
  static void do_free_by_irq_and_dev(
  	struct irq_entry *irq_entry,
  	unsigned int irq,
  	void *dev,
  	int flags
  )
  {
  	int i;
  	struct irq_fd *to_free;
  
  	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
  		if (irq_entry->irq_array[i] != NULL) {
  			if (
  			((flags & IGNORE_IRQ) ||
  				(irq_entry->irq_array[i]->irq == irq)) &&
  			((flags & IGNORE_DEV) ||
  				(irq_entry->irq_array[i]->id == dev))
  			) {
  				/* Turn off any IO on this fd - allows us to
  				 * avoid locking the IRQ loop
  				 */
  				os_del_epoll_fd(irq_entry->fd);
  				to_free = irq_entry->irq_array[i];
  				irq_entry->irq_array[i] = NULL;
  				assign_epoll_events_to_irq(irq_entry);
  				if (to_free->active)
  					to_free->purge = true;
  				else
  					kfree(to_free);
  			}
  		}
  	}
  }
  
  void free_irq_by_fd(int fd)
  {
  	struct irq_entry *to_free;
  	unsigned long flags;
  
  	spin_lock_irqsave(&irq_lock, flags);
  	to_free = get_irq_entry_by_fd(fd);
  	if (to_free != NULL) {
  		do_free_by_irq_and_dev(
  			to_free,
  			-1,
  			NULL,
  			IGNORE_IRQ | IGNORE_DEV
  		);
  	}
  	garbage_collect_irq_entries();
  	spin_unlock_irqrestore(&irq_lock, flags);
  }
  EXPORT_SYMBOL(free_irq_by_fd);
  
  static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
  {
  	struct irq_entry *to_free;
  	unsigned long flags;
  
  	spin_lock_irqsave(&irq_lock, flags);
  	to_free = active_fds;
  	while (to_free != NULL) {
  		do_free_by_irq_and_dev(
  			to_free,
  			irq,
  			dev,
  			0
  		);
  		to_free = to_free->next;
  	}
  	garbage_collect_irq_entries();
  	spin_unlock_irqrestore(&irq_lock, flags);
  }
  
  
  void deactivate_fd(int fd, int irqnum)
  {
  	struct irq_entry *to_free;
  	unsigned long flags;
  
  	os_del_epoll_fd(fd);
  	spin_lock_irqsave(&irq_lock, flags);
  	to_free = get_irq_entry_by_fd(fd);
  	if (to_free != NULL) {
  		do_free_by_irq_and_dev(
  			to_free,
  			irqnum,
  			NULL,
  			IGNORE_DEV
  		);
  	}
  	garbage_collect_irq_entries();
  	spin_unlock_irqrestore(&irq_lock, flags);
  	ignore_sigio_fd(fd);
  }
  EXPORT_SYMBOL(deactivate_fd);
  
  /*
   * Called just before shutdown in order to provide a clean exec
   * environment in case the system is rebooting.  No locking because
   * that would cause a pointless shutdown hang if something hadn't
   * released the lock.
   */
  int deactivate_all_fds(void)
  {
  	struct irq_entry *to_free;
  
  	/* Stop IO. The IRQ loop has no lock so this is our
  	 * only way of making sure we are safe to dispose
  	 * of all IRQ handlers
  	 */
  	os_set_ioignore();
  	to_free = active_fds;
  	while (to_free != NULL) {
  		do_free_by_irq_and_dev(
  			to_free,
  			-1,
  			NULL,
  			IGNORE_IRQ | IGNORE_DEV
  		);
  		to_free = to_free->next;
  	}
  	/* don't garbage collect - we can no longer call kfree() here */
  	os_close_epoll_fd();
  	return 0;
  }
  
  /*
   * do_IRQ handles all normal device IRQs (the special
   * SMP cross-CPU interrupts have their own specific
   * handlers).
   */
  unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
  {
  	struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
  	irq_enter();
  	generic_handle_irq(irq);
  	irq_exit();
  	set_irq_regs(old_regs);
  	return 1;
  }
  
  void um_free_irq(unsigned int irq, void *dev)
  {
  	free_irq_by_irq_and_dev(irq, dev);
  	free_irq(irq, dev);
  }
  EXPORT_SYMBOL(um_free_irq);
  
  int um_request_irq(unsigned int irq, int fd, int type,
  		   irq_handler_t handler,
  		   unsigned long irqflags, const char * devname,
  		   void *dev_id)
  {
  	int err;
  
  	if (fd != -1) {
  		err = activate_fd(irq, fd, type, dev_id);
  		if (err)
  			return err;
  	}
  
  	return request_irq(irq, handler, irqflags, devname, dev_id);
  }
  
  EXPORT_SYMBOL(um_request_irq);
  
  /*
   * irq_chip must define at least enable/disable and ack when
   * the edge handler is used.
   */
  static void dummy(struct irq_data *d)
  {
  }
  
  /* This is used for everything else than the timer. */
  static struct irq_chip normal_irq_type = {
  	.name = "SIGIO",
  	.irq_disable = dummy,
  	.irq_enable = dummy,
  	.irq_ack = dummy,
  	.irq_mask = dummy,
  	.irq_unmask = dummy,
  };
  
  static struct irq_chip SIGVTALRM_irq_type = {
  	.name = "SIGVTALRM",
  	.irq_disable = dummy,
  	.irq_enable = dummy,
  	.irq_ack = dummy,
  	.irq_mask = dummy,
  	.irq_unmask = dummy,
  };
  
  void __init init_IRQ(void)
  {
  	int i;
  
  	irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);
  
  
  	for (i = 1; i <= LAST_IRQ; i++)
  		irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
  	/* Initialize EPOLL Loop */
  	os_setup_epoll();
  }
  
  /*
   * IRQ stack entry and exit:
   *
   * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
   * and switch over to the IRQ stack after some preparation.  We use
   * sigaltstack to receive signals on a separate stack from the start.
   * These two functions make sure the rest of the kernel won't be too
   * upset by being on a different stack.  The IRQ stack has a
   * thread_info structure at the bottom so that current et al continue
   * to work.
   *
   * to_irq_stack copies the current task's thread_info to the IRQ stack
   * thread_info and sets the tasks's stack to point to the IRQ stack.
   *
   * from_irq_stack copies the thread_info struct back (flags may have
   * been modified) and resets the task's stack pointer.
   *
   * Tricky bits -
   *
   * What happens when two signals race each other?  UML doesn't block
   * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
   * could arrive while a previous one is still setting up the
   * thread_info.
   *
   * There are three cases -
   *     The first interrupt on the stack - sets up the thread_info and
   * handles the interrupt
   *     A nested interrupt interrupting the copying of the thread_info -
   * can't handle the interrupt, as the stack is in an unknown state
   *     A nested interrupt not interrupting the copying of the
   * thread_info - doesn't do any setup, just handles the interrupt
   *
   * The first job is to figure out whether we interrupted stack setup.
   * This is done by xchging the signal mask with thread_info->pending.
   * If the value that comes back is zero, then there is no setup in
   * progress, and the interrupt can be handled.  If the value is
   * non-zero, then there is stack setup in progress.  In order to have
   * the interrupt handled, we leave our signal in the mask, and it will
   * be handled by the upper handler after it has set up the stack.
   *
   * Next is to figure out whether we are the outer handler or a nested
   * one.  As part of setting up the stack, thread_info->real_thread is
   * set to non-NULL (and is reset to NULL on exit).  This is the
   * nesting indicator.  If it is non-NULL, then the stack is already
   * set up and the handler can run.
   */
  
  static unsigned long pending_mask;
  
  unsigned long to_irq_stack(unsigned long *mask_out)
  {
  	struct thread_info *ti;
  	unsigned long mask, old;
  	int nested;
  
  	mask = xchg(&pending_mask, *mask_out);
  	if (mask != 0) {
  		/*
  		 * If any interrupts come in at this point, we want to
  		 * make sure that their bits aren't lost by our
  		 * putting our bit in.  So, this loop accumulates bits
  		 * until xchg returns the same value that we put in.
  		 * When that happens, there were no new interrupts,
  		 * and pending_mask contains a bit for each interrupt
  		 * that came in.
  		 */
  		old = *mask_out;
  		do {
  			old |= mask;
  			mask = xchg(&pending_mask, old);
  		} while (mask != old);
  		return 1;
  	}
  
  	ti = current_thread_info();
  	nested = (ti->real_thread != NULL);
  	if (!nested) {
  		struct task_struct *task;
  		struct thread_info *tti;
  
  		task = cpu_tasks[ti->cpu].task;
  		tti = task_thread_info(task);
  
  		*ti = *tti;
  		ti->real_thread = tti;
  		task->stack = ti;
  	}
  
  	mask = xchg(&pending_mask, 0);
  	*mask_out |= mask | nested;
  	return 0;
  }
  
  unsigned long from_irq_stack(int nested)
  {
  	struct thread_info *ti, *to;
  	unsigned long mask;
  
  	ti = current_thread_info();
  
  	pending_mask = 1;
  
  	to = ti->real_thread;
  	current->stack = to;
  	ti->real_thread = NULL;
  	*to = *ti;
  
  	mask = xchg(&pending_mask, 0);
  	return mask & ~1;
  }
  
  