* launcher controls and communicates with the Guest. For example,
* the first write will tell us the Guest's memory layout and entry
* point. A read will run the Guest until something happens, such as
- * a signal or the Guest doing a NOTIFY out to the Launcher. There is
- * also a way for the Launcher to attach eventfds to particular NOTIFY
- * values instead of returning from the read() call.
+ * a signal or the Guest accessing a device.
:*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/sched.h>
-#include <linux/eventfd.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/export.h>
#include "lg.h"
-/*L:056
- * Before we move on, let's jump ahead and look at what the kernel does when
- * it needs to look up the eventfds. That will complete our picture of how we
- * use RCU.
- *
- * The notification value is in cpu->pending_notify: we return true if it went
- * to an eventfd.
- */
-bool send_notify_to_eventfd(struct lg_cpu *cpu)
-{
- unsigned int i;
- struct lg_eventfd_map *map;
-
- /* We only connect LHCALL_NOTIFY to event fds, not other traps. */
- if (cpu->pending.trap != LGUEST_TRAP_ENTRY)
- return false;
-
- /*
- * This "rcu_read_lock()" helps track when someone is still looking at
- * the (RCU-using) eventfds array. It's not actually a lock at all;
- * indeed it's a noop in many configurations. (You didn't expect me to
- * explain all the RCU secrets here, did you?)
- */
- rcu_read_lock();
- /*
- * rcu_dereference is the counter-side of rcu_assign_pointer(); it
- * makes sure we don't access the memory pointed to by
- * cpu->lg->eventfds before cpu->lg->eventfds is set. Sounds crazy,
- * but Alpha allows this! Paul McKenney points out that a really
- * aggressive compiler could have the same effect:
- * http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html
- *
- * So play safe, use rcu_dereference to get the rcu-protected pointer:
- */
- map = rcu_dereference(cpu->lg->eventfds);
- /*
- * Simple array search: even if they add an eventfd while we do this,
- * we'll continue to use the old array and just won't see the new one.
- */
- for (i = 0; i < map->num; i++) {
- if (map->map[i].addr == cpu->pending.addr) {
- eventfd_signal(map->map[i].event, 1);
- cpu->pending.trap = 0;
- break;
- }
- }
- /* We're done with the rcu-protected variable cpu->lg->eventfds. */
- rcu_read_unlock();
-
- /* If we cleared the notification, it's because we found a match. */
- return cpu->pending.trap == 0;
-}
-
-/*L:055
- * One of the more tricksy tricks in the Linux Kernel is a technique called
- * Read Copy Update. Since one point of lguest is to teach lguest journeyers
- * about kernel coding, I use it here. (In case you're curious, other purposes
- * include learning about virtualization and instilling a deep appreciation for
- * simplicity and puppies).
- *
- * We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we
- * add new eventfds without ever blocking readers from accessing the array.
- * The current Launcher only does this during boot, so that never happens. But
- * Read Copy Update is cool, and adding a lock risks damaging even more puppies
- * than this code does.
- *
- * We allocate a brand new one-larger array, copy the old one and add our new
- * element. Then we make the lg eventfd pointer point to the new array.
- * That's the easy part: now we need to free the old one, but we need to make
- * sure no slow CPU somewhere is still looking at it. That's what
- * synchronize_rcu does for us: waits until every CPU has indicated that it has
- * moved on to know it's no longer using the old one.
- *
- * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
- */
-static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
-{
- struct lg_eventfd_map *new, *old = lg->eventfds;
-
- /*
- * We don't allow notifications on value 0 anyway (pending_notify of
- * 0 means "nothing pending").
- */
- if (!addr)
- return -EINVAL;
-
- /*
- * Replace the old array with the new one, carefully: others can
- * be accessing it at the same time.
- */
- new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
- GFP_KERNEL);
- if (!new)
- return -ENOMEM;
-
- /* First make identical copy. */
- memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
- new->num = old->num;
-
- /* Now append new entry. */
- new->map[new->num].addr = addr;
- new->map[new->num].event = eventfd_ctx_fdget(fd);
- if (IS_ERR(new->map[new->num].event)) {
- int err = PTR_ERR(new->map[new->num].event);
- kfree(new);
- return err;
- }
- new->num++;
-
- /*
- * Now put new one in place: rcu_assign_pointer() is a fancy way of
- * doing "lg->eventfds = new", but it uses memory barriers to make
- * absolutely sure that the contents of "new" written above is nailed
- * down before we actually do the assignment.
- *
- * We have to think about these kinds of things when we're operating on
- * live data without locks.
- */
- rcu_assign_pointer(lg->eventfds, new);
-
- /*
- * We're not in a big hurry. Wait until no one's looking at old
- * version, then free it.
- */
- synchronize_rcu();
- kfree(old);
-
- return 0;
-}
-
/*L:052
- * Receiving notifications from the Guest is usually done by attaching a
- * particular LHCALL_NOTIFY value to an event filedescriptor. The eventfd will
- * become readable when the Guest does an LHCALL_NOTIFY with that value.
- *
- * This is really convenient for processing each virtqueue in a separate
- * thread.
- */
-static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
-{
- unsigned long addr, fd;
- int err;
-
- if (get_user(addr, input) != 0)
- return -EFAULT;
- input++;
- if (get_user(fd, input) != 0)
- return -EFAULT;
-
- /*
- * Just make sure two callers don't add eventfds at once. We really
- * only need to lock against callers adding to the same Guest, so using
- * the Big Lguest Lock is overkill. But this is setup, not a fast path.
- */
- mutex_lock(&lguest_lock);
- err = add_eventfd(lg, addr, fd);
- mutex_unlock(&lguest_lock);
-
- return err;
-}
-
-/* The Launcher can get the registers, and also set some of them. */
+ The Launcher can get the registers, and also set some of them.
+*/
static int getreg_setup(struct lg_cpu *cpu, const unsigned long __user *input)
{
unsigned long which;
goto unlock;
}
- lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
- if (!lg->eventfds) {
- err = -ENOMEM;
- goto free_lg;
- }
- lg->eventfds->num = 0;
-
/* Populate the easy fields of our "struct lguest" */
lg->mem_base = (void __user *)args[0];
lg->pfn_limit = args[1];
/* This is the first cpu (cpu 0) and it will start booting at args[2] */
err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
if (err)
- goto free_eventfds;
+ goto free_lg;
/*
* Initialize the Guest's shadow page tables. This allocates
free_regs:
/* FIXME: This should be in free_vcpu */
free_page(lg->cpus[0].regs_page);
-free_eventfds:
- kfree(lg->eventfds);
free_lg:
kfree(lg);
unlock:
return initialize(file, input);
case LHREQ_IRQ:
return user_send_irq(cpu, input);
- case LHREQ_EVENTFD:
- return attach_eventfd(lg, input);
case LHREQ_GETREG:
return getreg_setup(cpu, input);
case LHREQ_SETREG:
mmput(lg->cpus[i].mm);
}
- /* Release any eventfds they registered. */
- for (i = 0; i < lg->eventfds->num; i++)
- eventfd_ctx_put(lg->eventfds->map[i].event);
- kfree(lg->eventfds);
-
/*
* If lg->dead doesn't contain an error code it will be NULL or a
* kmalloc()ed string, either of which is ok to hand to kfree().
projects / linux-drm-fsl-dcu.git / commitdiff