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![Cosmin Paraschiv](/assets/img/avatar_default.png)
Make the container_of call friendlier and fix some comment slip-ups. Signed-off-by: Cosmin Paraschiv <csmnprschv@gmail.com> Cc: Daniel Baluta <dbaluta@ixiacom.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
542 lines
16 KiB
C
542 lines
16 KiB
C
/*P:200 This contains all the /dev/lguest code, whereby the userspace
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* launcher controls and communicates with the Guest. For example,
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* the first write will tell us the Guest's memory layout and entry
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* point. A read will run the Guest until something happens, such as
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* a signal or the Guest doing a NOTIFY out to the Launcher. There is
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* also a way for the Launcher to attach eventfds to particular NOTIFY
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* values instead of returning from the read() call.
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:*/
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#include <linux/uaccess.h>
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#include <linux/miscdevice.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/eventfd.h>
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#include <linux/file.h>
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#include <linux/slab.h>
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#include <linux/export.h>
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#include "lg.h"
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/*L:056
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* Before we move on, let's jump ahead and look at what the kernel does when
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* it needs to look up the eventfds. That will complete our picture of how we
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* use RCU.
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*
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* The notification value is in cpu->pending_notify: we return true if it went
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* to an eventfd.
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*/
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bool send_notify_to_eventfd(struct lg_cpu *cpu)
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{
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unsigned int i;
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struct lg_eventfd_map *map;
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/*
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* This "rcu_read_lock()" helps track when someone is still looking at
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* the (RCU-using) eventfds array. It's not actually a lock at all;
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* indeed it's a noop in many configurations. (You didn't expect me to
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* explain all the RCU secrets here, did you?)
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*/
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rcu_read_lock();
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/*
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* rcu_dereference is the counter-side of rcu_assign_pointer(); it
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* makes sure we don't access the memory pointed to by
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* cpu->lg->eventfds before cpu->lg->eventfds is set. Sounds crazy,
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* but Alpha allows this! Paul McKenney points out that a really
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* aggressive compiler could have the same effect:
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* http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html
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*
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* So play safe, use rcu_dereference to get the rcu-protected pointer:
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*/
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map = rcu_dereference(cpu->lg->eventfds);
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/*
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* Simple array search: even if they add an eventfd while we do this,
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* we'll continue to use the old array and just won't see the new one.
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*/
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for (i = 0; i < map->num; i++) {
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if (map->map[i].addr == cpu->pending_notify) {
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eventfd_signal(map->map[i].event, 1);
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cpu->pending_notify = 0;
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break;
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}
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}
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/* We're done with the rcu-protected variable cpu->lg->eventfds. */
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rcu_read_unlock();
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/* If we cleared the notification, it's because we found a match. */
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return cpu->pending_notify == 0;
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}
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/*L:055
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* One of the more tricksy tricks in the Linux Kernel is a technique called
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* Read Copy Update. Since one point of lguest is to teach lguest journeyers
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* about kernel coding, I use it here. (In case you're curious, other purposes
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* include learning about virtualization and instilling a deep appreciation for
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* simplicity and puppies).
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*
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* We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we
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* add new eventfds without ever blocking readers from accessing the array.
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* The current Launcher only does this during boot, so that never happens. But
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* Read Copy Update is cool, and adding a lock risks damaging even more puppies
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* than this code does.
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*
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* We allocate a brand new one-larger array, copy the old one and add our new
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* element. Then we make the lg eventfd pointer point to the new array.
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* That's the easy part: now we need to free the old one, but we need to make
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* sure no slow CPU somewhere is still looking at it. That's what
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* synchronize_rcu does for us: waits until every CPU has indicated that it has
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* moved on to know it's no longer using the old one.
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*
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* If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
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*/
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static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
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{
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struct lg_eventfd_map *new, *old = lg->eventfds;
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/*
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* We don't allow notifications on value 0 anyway (pending_notify of
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* 0 means "nothing pending").
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*/
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if (!addr)
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return -EINVAL;
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/*
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* Replace the old array with the new one, carefully: others can
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* be accessing it at the same time.
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*/
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new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
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GFP_KERNEL);
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if (!new)
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return -ENOMEM;
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/* First make identical copy. */
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memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
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new->num = old->num;
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/* Now append new entry. */
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new->map[new->num].addr = addr;
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new->map[new->num].event = eventfd_ctx_fdget(fd);
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if (IS_ERR(new->map[new->num].event)) {
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int err = PTR_ERR(new->map[new->num].event);
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kfree(new);
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return err;
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}
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new->num++;
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/*
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* Now put new one in place: rcu_assign_pointer() is a fancy way of
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* doing "lg->eventfds = new", but it uses memory barriers to make
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* absolutely sure that the contents of "new" written above is nailed
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* down before we actually do the assignment.
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*
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* We have to think about these kinds of things when we're operating on
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* live data without locks.
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*/
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rcu_assign_pointer(lg->eventfds, new);
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/*
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* We're not in a big hurry. Wait until no one's looking at old
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* version, then free it.
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*/
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synchronize_rcu();
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kfree(old);
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return 0;
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}
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/*L:052
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* Receiving notifications from the Guest is usually done by attaching a
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* particular LHCALL_NOTIFY value to an event filedescriptor. The eventfd will
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* become readable when the Guest does an LHCALL_NOTIFY with that value.
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*
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* This is really convenient for processing each virtqueue in a separate
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* thread.
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*/
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static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
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{
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unsigned long addr, fd;
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int err;
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if (get_user(addr, input) != 0)
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return -EFAULT;
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input++;
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if (get_user(fd, input) != 0)
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return -EFAULT;
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/*
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* Just make sure two callers don't add eventfds at once. We really
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* only need to lock against callers adding to the same Guest, so using
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* the Big Lguest Lock is overkill. But this is setup, not a fast path.
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*/
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mutex_lock(&lguest_lock);
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err = add_eventfd(lg, addr, fd);
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mutex_unlock(&lguest_lock);
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return err;
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}
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/*L:050
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* Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
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* number to /dev/lguest.
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*/
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static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
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{
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unsigned long irq;
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if (get_user(irq, input) != 0)
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return -EFAULT;
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if (irq >= LGUEST_IRQS)
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return -EINVAL;
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/*
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* Next time the Guest runs, the core code will see if it can deliver
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* this interrupt.
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*/
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set_interrupt(cpu, irq);
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return 0;
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}
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/*L:040
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* Once our Guest is initialized, the Launcher makes it run by reading
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* from /dev/lguest.
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*/
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static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
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{
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struct lguest *lg = file->private_data;
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struct lg_cpu *cpu;
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unsigned int cpu_id = *o;
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/* You must write LHREQ_INITIALIZE first! */
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if (!lg)
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return -EINVAL;
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/* Watch out for arbitrary vcpu indexes! */
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if (cpu_id >= lg->nr_cpus)
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return -EINVAL;
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cpu = &lg->cpus[cpu_id];
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/* If you're not the task which owns the Guest, go away. */
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if (current != cpu->tsk)
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return -EPERM;
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/* If the Guest is already dead, we indicate why */
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if (lg->dead) {
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size_t len;
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/* lg->dead either contains an error code, or a string. */
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if (IS_ERR(lg->dead))
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return PTR_ERR(lg->dead);
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/* We can only return as much as the buffer they read with. */
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len = min(size, strlen(lg->dead)+1);
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if (copy_to_user(user, lg->dead, len) != 0)
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return -EFAULT;
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return len;
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}
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/*
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* If we returned from read() last time because the Guest sent I/O,
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* clear the flag.
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*/
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if (cpu->pending_notify)
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cpu->pending_notify = 0;
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/* Run the Guest until something interesting happens. */
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return run_guest(cpu, (unsigned long __user *)user);
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}
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/*L:025
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* This actually initializes a CPU. For the moment, a Guest is only
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* uniprocessor, so "id" is always 0.
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*/
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static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
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{
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/* We have a limited number of CPUs in the lguest struct. */
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if (id >= ARRAY_SIZE(cpu->lg->cpus))
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return -EINVAL;
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/* Set up this CPU's id, and pointer back to the lguest struct. */
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cpu->id = id;
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cpu->lg = container_of(cpu, struct lguest, cpus[id]);
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cpu->lg->nr_cpus++;
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/* Each CPU has a timer it can set. */
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init_clockdev(cpu);
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/*
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* We need a complete page for the Guest registers: they are accessible
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* to the Guest and we can only grant it access to whole pages.
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*/
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cpu->regs_page = get_zeroed_page(GFP_KERNEL);
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if (!cpu->regs_page)
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return -ENOMEM;
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/* We actually put the registers at the end of the page. */
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cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
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/*
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* Now we initialize the Guest's registers, handing it the start
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* address.
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*/
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lguest_arch_setup_regs(cpu, start_ip);
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/*
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* We keep a pointer to the Launcher task (ie. current task) for when
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* other Guests want to wake this one (eg. console input).
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*/
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cpu->tsk = current;
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/*
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* We need to keep a pointer to the Launcher's memory map, because if
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* the Launcher dies we need to clean it up. If we don't keep a
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* reference, it is destroyed before close() is called.
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*/
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cpu->mm = get_task_mm(cpu->tsk);
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/*
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* We remember which CPU's pages this Guest used last, for optimization
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* when the same Guest runs on the same CPU twice.
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*/
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cpu->last_pages = NULL;
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/* No error == success. */
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return 0;
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}
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/*L:020
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* The initialization write supplies 3 pointer sized (32 or 64 bit) values (in
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* addition to the LHREQ_INITIALIZE value). These are:
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*
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* base: The start of the Guest-physical memory inside the Launcher memory.
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*
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* pfnlimit: The highest (Guest-physical) page number the Guest should be
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* allowed to access. The Guest memory lives inside the Launcher, so it sets
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* this to ensure the Guest can only reach its own memory.
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*
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* start: The first instruction to execute ("eip" in x86-speak).
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*/
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static int initialize(struct file *file, const unsigned long __user *input)
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{
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/* "struct lguest" contains all we (the Host) know about a Guest. */
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struct lguest *lg;
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int err;
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unsigned long args[3];
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/*
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* We grab the Big Lguest lock, which protects against multiple
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* simultaneous initializations.
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*/
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mutex_lock(&lguest_lock);
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/* You can't initialize twice! Close the device and start again... */
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if (file->private_data) {
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err = -EBUSY;
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goto unlock;
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}
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if (copy_from_user(args, input, sizeof(args)) != 0) {
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err = -EFAULT;
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goto unlock;
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}
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lg = kzalloc(sizeof(*lg), GFP_KERNEL);
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if (!lg) {
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err = -ENOMEM;
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goto unlock;
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}
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lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
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if (!lg->eventfds) {
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err = -ENOMEM;
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goto free_lg;
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}
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lg->eventfds->num = 0;
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/* Populate the easy fields of our "struct lguest" */
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lg->mem_base = (void __user *)args[0];
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lg->pfn_limit = args[1];
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/* This is the first cpu (cpu 0) and it will start booting at args[2] */
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err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
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if (err)
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goto free_eventfds;
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/*
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* Initialize the Guest's shadow page tables. This allocates
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* memory, so can fail.
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*/
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err = init_guest_pagetable(lg);
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if (err)
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goto free_regs;
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/* We keep our "struct lguest" in the file's private_data. */
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file->private_data = lg;
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mutex_unlock(&lguest_lock);
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/* And because this is a write() call, we return the length used. */
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return sizeof(args);
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free_regs:
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/* FIXME: This should be in free_vcpu */
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free_page(lg->cpus[0].regs_page);
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free_eventfds:
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kfree(lg->eventfds);
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free_lg:
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kfree(lg);
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unlock:
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mutex_unlock(&lguest_lock);
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return err;
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}
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/*L:010
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* The first operation the Launcher does must be a write. All writes
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* start with an unsigned long number: for the first write this must be
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* LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
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* writes of other values to send interrupts or set up receipt of notifications.
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*
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* Note that we overload the "offset" in the /dev/lguest file to indicate what
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* CPU number we're dealing with. Currently this is always 0 since we only
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* support uniprocessor Guests, but you can see the beginnings of SMP support
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* here.
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*/
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static ssize_t write(struct file *file, const char __user *in,
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size_t size, loff_t *off)
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{
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/*
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* Once the Guest is initialized, we hold the "struct lguest" in the
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* file private data.
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*/
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struct lguest *lg = file->private_data;
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const unsigned long __user *input = (const unsigned long __user *)in;
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unsigned long req;
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struct lg_cpu *uninitialized_var(cpu);
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unsigned int cpu_id = *off;
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/* The first value tells us what this request is. */
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if (get_user(req, input) != 0)
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return -EFAULT;
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input++;
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/* If you haven't initialized, you must do that first. */
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if (req != LHREQ_INITIALIZE) {
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if (!lg || (cpu_id >= lg->nr_cpus))
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return -EINVAL;
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cpu = &lg->cpus[cpu_id];
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/* Once the Guest is dead, you can only read() why it died. */
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if (lg->dead)
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return -ENOENT;
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}
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switch (req) {
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case LHREQ_INITIALIZE:
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return initialize(file, input);
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case LHREQ_IRQ:
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return user_send_irq(cpu, input);
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case LHREQ_EVENTFD:
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return attach_eventfd(lg, input);
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default:
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return -EINVAL;
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}
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}
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/*L:060
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* The final piece of interface code is the close() routine. It reverses
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* everything done in initialize(). This is usually called because the
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* Launcher exited.
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*
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* Note that the close routine returns 0 or a negative error number: it can't
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* really fail, but it can whine. I blame Sun for this wart, and K&R C for
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* letting them do it.
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:*/
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static int close(struct inode *inode, struct file *file)
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{
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struct lguest *lg = file->private_data;
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unsigned int i;
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/* If we never successfully initialized, there's nothing to clean up */
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if (!lg)
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return 0;
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/*
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* We need the big lock, to protect from inter-guest I/O and other
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* Launchers initializing guests.
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*/
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mutex_lock(&lguest_lock);
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/* Free up the shadow page tables for the Guest. */
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free_guest_pagetable(lg);
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for (i = 0; i < lg->nr_cpus; i++) {
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/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
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hrtimer_cancel(&lg->cpus[i].hrt);
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/* We can free up the register page we allocated. */
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free_page(lg->cpus[i].regs_page);
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/*
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* Now all the memory cleanups are done, it's safe to release
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* the Launcher's memory management structure.
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*/
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mmput(lg->cpus[i].mm);
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}
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/* Release any eventfds they registered. */
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for (i = 0; i < lg->eventfds->num; i++)
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eventfd_ctx_put(lg->eventfds->map[i].event);
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kfree(lg->eventfds);
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/*
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* If lg->dead doesn't contain an error code it will be NULL or a
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* kmalloc()ed string, either of which is ok to hand to kfree().
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*/
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if (!IS_ERR(lg->dead))
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kfree(lg->dead);
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/* Free the memory allocated to the lguest_struct */
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kfree(lg);
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/* Release lock and exit. */
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mutex_unlock(&lguest_lock);
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return 0;
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}
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/*L:000
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* Welcome to our journey through the Launcher!
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*
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* The Launcher is the Host userspace program which sets up, runs and services
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* the Guest. In fact, many comments in the Drivers which refer to "the Host"
|
|
* doing things are inaccurate: the Launcher does all the device handling for
|
|
* the Guest, but the Guest can't know that.
|
|
*
|
|
* Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
|
|
* shall see more of that later.
|
|
*
|
|
* We begin our understanding with the Host kernel interface which the Launcher
|
|
* uses: reading and writing a character device called /dev/lguest. All the
|
|
* work happens in the read(), write() and close() routines:
|
|
*/
|
|
static const struct file_operations lguest_fops = {
|
|
.owner = THIS_MODULE,
|
|
.release = close,
|
|
.write = write,
|
|
.read = read,
|
|
.llseek = default_llseek,
|
|
};
|
|
/*:*/
|
|
|
|
/*
|
|
* This is a textbook example of a "misc" character device. Populate a "struct
|
|
* miscdevice" and register it with misc_register().
|
|
*/
|
|
static struct miscdevice lguest_dev = {
|
|
.minor = MISC_DYNAMIC_MINOR,
|
|
.name = "lguest",
|
|
.fops = &lguest_fops,
|
|
};
|
|
|
|
int __init lguest_device_init(void)
|
|
{
|
|
return misc_register(&lguest_dev);
|
|
}
|
|
|
|
void __exit lguest_device_remove(void)
|
|
{
|
|
misc_deregister(&lguest_dev);
|
|
}
|