linux-stable/virt/kvm/eventfd.c
Michael S. Tsirkin bd2b53b20f KVM: fast-path msi injection with irqfd
Store irq routing table pointer in the irqfd object,
and use that to inject MSI directly without bouncing out to
a kernel thread.

While we touch this structure, rearrange irqfd fields to make fastpath
better packed for better cache utilization.

This also adds some comments about locking rules and rcu usage in code.

Some notes on the design:
- Use pointer into the rt instead of copying an entry,
  to make it possible to use rcu, thus side-stepping
  locking complexities.  We also save some memory this way.
- Old workqueue code is still used for level irqs.
  I don't think we DTRT with level anyway, however,
  it seems easier to keep the code around as
  it has been thought through and debugged, and fix level later than
  rip out and re-instate it later.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
2011-01-12 11:29:38 +02:00

655 lines
15 KiB
C

/*
* kvm eventfd support - use eventfd objects to signal various KVM events
*
* Copyright 2009 Novell. All Rights Reserved.
* Copyright 2010 Red Hat, Inc. and/or its affiliates.
*
* Author:
* Gregory Haskins <ghaskins@novell.com>
*
* This file is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <linux/kvm_host.h>
#include <linux/kvm.h>
#include <linux/workqueue.h>
#include <linux/syscalls.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/list.h>
#include <linux/eventfd.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include "iodev.h"
/*
* --------------------------------------------------------------------
* irqfd: Allows an fd to be used to inject an interrupt to the guest
*
* Credit goes to Avi Kivity for the original idea.
* --------------------------------------------------------------------
*/
struct _irqfd {
/* Used for MSI fast-path */
struct kvm *kvm;
wait_queue_t wait;
/* Update side is protected by irqfds.lock */
struct kvm_kernel_irq_routing_entry __rcu *irq_entry;
/* Used for level IRQ fast-path */
int gsi;
struct work_struct inject;
/* Used for setup/shutdown */
struct eventfd_ctx *eventfd;
struct list_head list;
poll_table pt;
struct work_struct shutdown;
};
static struct workqueue_struct *irqfd_cleanup_wq;
static void
irqfd_inject(struct work_struct *work)
{
struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
struct kvm *kvm = irqfd->kvm;
kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
}
/*
* Race-free decouple logic (ordering is critical)
*/
static void
irqfd_shutdown(struct work_struct *work)
{
struct _irqfd *irqfd = container_of(work, struct _irqfd, shutdown);
u64 cnt;
/*
* Synchronize with the wait-queue and unhook ourselves to prevent
* further events.
*/
eventfd_ctx_remove_wait_queue(irqfd->eventfd, &irqfd->wait, &cnt);
/*
* We know no new events will be scheduled at this point, so block
* until all previously outstanding events have completed
*/
flush_work(&irqfd->inject);
/*
* It is now safe to release the object's resources
*/
eventfd_ctx_put(irqfd->eventfd);
kfree(irqfd);
}
/* assumes kvm->irqfds.lock is held */
static bool
irqfd_is_active(struct _irqfd *irqfd)
{
return list_empty(&irqfd->list) ? false : true;
}
/*
* Mark the irqfd as inactive and schedule it for removal
*
* assumes kvm->irqfds.lock is held
*/
static void
irqfd_deactivate(struct _irqfd *irqfd)
{
BUG_ON(!irqfd_is_active(irqfd));
list_del_init(&irqfd->list);
queue_work(irqfd_cleanup_wq, &irqfd->shutdown);
}
/*
* Called with wqh->lock held and interrupts disabled
*/
static int
irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
unsigned long flags = (unsigned long)key;
struct kvm_kernel_irq_routing_entry *irq;
struct kvm *kvm = irqfd->kvm;
if (flags & POLLIN) {
rcu_read_lock();
irq = rcu_dereference(irqfd->irq_entry);
/* An event has been signaled, inject an interrupt */
if (irq)
kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
else
schedule_work(&irqfd->inject);
rcu_read_unlock();
}
if (flags & POLLHUP) {
/* The eventfd is closing, detach from KVM */
unsigned long flags;
spin_lock_irqsave(&kvm->irqfds.lock, flags);
/*
* We must check if someone deactivated the irqfd before
* we could acquire the irqfds.lock since the item is
* deactivated from the KVM side before it is unhooked from
* the wait-queue. If it is already deactivated, we can
* simply return knowing the other side will cleanup for us.
* We cannot race against the irqfd going away since the
* other side is required to acquire wqh->lock, which we hold
*/
if (irqfd_is_active(irqfd))
irqfd_deactivate(irqfd);
spin_unlock_irqrestore(&kvm->irqfds.lock, flags);
}
return 0;
}
static void
irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
poll_table *pt)
{
struct _irqfd *irqfd = container_of(pt, struct _irqfd, pt);
add_wait_queue(wqh, &irqfd->wait);
}
/* Must be called under irqfds.lock */
static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
struct kvm_irq_routing_table *irq_rt)
{
struct kvm_kernel_irq_routing_entry *e;
struct hlist_node *n;
if (irqfd->gsi >= irq_rt->nr_rt_entries) {
rcu_assign_pointer(irqfd->irq_entry, NULL);
return;
}
hlist_for_each_entry(e, n, &irq_rt->map[irqfd->gsi], link) {
/* Only fast-path MSI. */
if (e->type == KVM_IRQ_ROUTING_MSI)
rcu_assign_pointer(irqfd->irq_entry, e);
else
rcu_assign_pointer(irqfd->irq_entry, NULL);
}
}
static int
kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
{
struct kvm_irq_routing_table *irq_rt;
struct _irqfd *irqfd, *tmp;
struct file *file = NULL;
struct eventfd_ctx *eventfd = NULL;
int ret;
unsigned int events;
irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
if (!irqfd)
return -ENOMEM;
irqfd->kvm = kvm;
irqfd->gsi = gsi;
INIT_LIST_HEAD(&irqfd->list);
INIT_WORK(&irqfd->inject, irqfd_inject);
INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
file = eventfd_fget(fd);
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto fail;
}
eventfd = eventfd_ctx_fileget(file);
if (IS_ERR(eventfd)) {
ret = PTR_ERR(eventfd);
goto fail;
}
irqfd->eventfd = eventfd;
/*
* Install our own custom wake-up handling so we are notified via
* a callback whenever someone signals the underlying eventfd
*/
init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
spin_lock_irq(&kvm->irqfds.lock);
ret = 0;
list_for_each_entry(tmp, &kvm->irqfds.items, list) {
if (irqfd->eventfd != tmp->eventfd)
continue;
/* This fd is used for another irq already. */
ret = -EBUSY;
spin_unlock_irq(&kvm->irqfds.lock);
goto fail;
}
irq_rt = rcu_dereference_protected(kvm->irq_routing,
lockdep_is_held(&kvm->irqfds.lock));
irqfd_update(kvm, irqfd, irq_rt);
events = file->f_op->poll(file, &irqfd->pt);
list_add_tail(&irqfd->list, &kvm->irqfds.items);
/*
* Check if there was an event already pending on the eventfd
* before we registered, and trigger it as if we didn't miss it.
*/
if (events & POLLIN)
schedule_work(&irqfd->inject);
spin_unlock_irq(&kvm->irqfds.lock);
/*
* do not drop the file until the irqfd is fully initialized, otherwise
* we might race against the POLLHUP
*/
fput(file);
return 0;
fail:
if (eventfd && !IS_ERR(eventfd))
eventfd_ctx_put(eventfd);
if (!IS_ERR(file))
fput(file);
kfree(irqfd);
return ret;
}
void
kvm_eventfd_init(struct kvm *kvm)
{
spin_lock_init(&kvm->irqfds.lock);
INIT_LIST_HEAD(&kvm->irqfds.items);
INIT_LIST_HEAD(&kvm->ioeventfds);
}
/*
* shutdown any irqfd's that match fd+gsi
*/
static int
kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
{
struct _irqfd *irqfd, *tmp;
struct eventfd_ctx *eventfd;
eventfd = eventfd_ctx_fdget(fd);
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
spin_lock_irq(&kvm->irqfds.lock);
list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
if (irqfd->eventfd == eventfd && irqfd->gsi == gsi) {
/*
* This rcu_assign_pointer is needed for when
* another thread calls kvm_irqfd_update before
* we flush workqueue below.
* It is paired with synchronize_rcu done by caller
* of that function.
*/
rcu_assign_pointer(irqfd->irq_entry, NULL);
irqfd_deactivate(irqfd);
}
}
spin_unlock_irq(&kvm->irqfds.lock);
eventfd_ctx_put(eventfd);
/*
* Block until we know all outstanding shutdown jobs have completed
* so that we guarantee there will not be any more interrupts on this
* gsi once this deassign function returns.
*/
flush_workqueue(irqfd_cleanup_wq);
return 0;
}
int
kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
{
if (flags & KVM_IRQFD_FLAG_DEASSIGN)
return kvm_irqfd_deassign(kvm, fd, gsi);
return kvm_irqfd_assign(kvm, fd, gsi);
}
/*
* This function is called as the kvm VM fd is being released. Shutdown all
* irqfds that still remain open
*/
void
kvm_irqfd_release(struct kvm *kvm)
{
struct _irqfd *irqfd, *tmp;
spin_lock_irq(&kvm->irqfds.lock);
list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list)
irqfd_deactivate(irqfd);
spin_unlock_irq(&kvm->irqfds.lock);
/*
* Block until we know all outstanding shutdown jobs have completed
* since we do not take a kvm* reference.
*/
flush_workqueue(irqfd_cleanup_wq);
}
/*
* Change irq_routing and irqfd.
* Caller must invoke synchronize_rcu afterwards.
*/
void kvm_irq_routing_update(struct kvm *kvm,
struct kvm_irq_routing_table *irq_rt)
{
struct _irqfd *irqfd;
spin_lock_irq(&kvm->irqfds.lock);
rcu_assign_pointer(kvm->irq_routing, irq_rt);
list_for_each_entry(irqfd, &kvm->irqfds.items, list)
irqfd_update(kvm, irqfd, irq_rt);
spin_unlock_irq(&kvm->irqfds.lock);
}
/*
* create a host-wide workqueue for issuing deferred shutdown requests
* aggregated from all vm* instances. We need our own isolated single-thread
* queue to prevent deadlock against flushing the normal work-queue.
*/
static int __init irqfd_module_init(void)
{
irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup");
if (!irqfd_cleanup_wq)
return -ENOMEM;
return 0;
}
static void __exit irqfd_module_exit(void)
{
destroy_workqueue(irqfd_cleanup_wq);
}
module_init(irqfd_module_init);
module_exit(irqfd_module_exit);
/*
* --------------------------------------------------------------------
* ioeventfd: translate a PIO/MMIO memory write to an eventfd signal.
*
* userspace can register a PIO/MMIO address with an eventfd for receiving
* notification when the memory has been touched.
* --------------------------------------------------------------------
*/
struct _ioeventfd {
struct list_head list;
u64 addr;
int length;
struct eventfd_ctx *eventfd;
u64 datamatch;
struct kvm_io_device dev;
bool wildcard;
};
static inline struct _ioeventfd *
to_ioeventfd(struct kvm_io_device *dev)
{
return container_of(dev, struct _ioeventfd, dev);
}
static void
ioeventfd_release(struct _ioeventfd *p)
{
eventfd_ctx_put(p->eventfd);
list_del(&p->list);
kfree(p);
}
static bool
ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val)
{
u64 _val;
if (!(addr == p->addr && len == p->length))
/* address-range must be precise for a hit */
return false;
if (p->wildcard)
/* all else equal, wildcard is always a hit */
return true;
/* otherwise, we have to actually compare the data */
BUG_ON(!IS_ALIGNED((unsigned long)val, len));
switch (len) {
case 1:
_val = *(u8 *)val;
break;
case 2:
_val = *(u16 *)val;
break;
case 4:
_val = *(u32 *)val;
break;
case 8:
_val = *(u64 *)val;
break;
default:
return false;
}
return _val == p->datamatch ? true : false;
}
/* MMIO/PIO writes trigger an event if the addr/val match */
static int
ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len,
const void *val)
{
struct _ioeventfd *p = to_ioeventfd(this);
if (!ioeventfd_in_range(p, addr, len, val))
return -EOPNOTSUPP;
eventfd_signal(p->eventfd, 1);
return 0;
}
/*
* This function is called as KVM is completely shutting down. We do not
* need to worry about locking just nuke anything we have as quickly as possible
*/
static void
ioeventfd_destructor(struct kvm_io_device *this)
{
struct _ioeventfd *p = to_ioeventfd(this);
ioeventfd_release(p);
}
static const struct kvm_io_device_ops ioeventfd_ops = {
.write = ioeventfd_write,
.destructor = ioeventfd_destructor,
};
/* assumes kvm->slots_lock held */
static bool
ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p)
{
struct _ioeventfd *_p;
list_for_each_entry(_p, &kvm->ioeventfds, list)
if (_p->addr == p->addr && _p->length == p->length &&
(_p->wildcard || p->wildcard ||
_p->datamatch == p->datamatch))
return true;
return false;
}
static int
kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
enum kvm_bus bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
struct _ioeventfd *p;
struct eventfd_ctx *eventfd;
int ret;
/* must be natural-word sized */
switch (args->len) {
case 1:
case 2:
case 4:
case 8:
break;
default:
return -EINVAL;
}
/* check for range overflow */
if (args->addr + args->len < args->addr)
return -EINVAL;
/* check for extra flags that we don't understand */
if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK)
return -EINVAL;
eventfd = eventfd_ctx_fdget(args->fd);
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
p = kzalloc(sizeof(*p), GFP_KERNEL);
if (!p) {
ret = -ENOMEM;
goto fail;
}
INIT_LIST_HEAD(&p->list);
p->addr = args->addr;
p->length = args->len;
p->eventfd = eventfd;
/* The datamatch feature is optional, otherwise this is a wildcard */
if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH)
p->datamatch = args->datamatch;
else
p->wildcard = true;
mutex_lock(&kvm->slots_lock);
/* Verify that there isnt a match already */
if (ioeventfd_check_collision(kvm, p)) {
ret = -EEXIST;
goto unlock_fail;
}
kvm_iodevice_init(&p->dev, &ioeventfd_ops);
ret = kvm_io_bus_register_dev(kvm, bus_idx, &p->dev);
if (ret < 0)
goto unlock_fail;
list_add_tail(&p->list, &kvm->ioeventfds);
mutex_unlock(&kvm->slots_lock);
return 0;
unlock_fail:
mutex_unlock(&kvm->slots_lock);
fail:
kfree(p);
eventfd_ctx_put(eventfd);
return ret;
}
static int
kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
enum kvm_bus bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
struct _ioeventfd *p, *tmp;
struct eventfd_ctx *eventfd;
int ret = -ENOENT;
eventfd = eventfd_ctx_fdget(args->fd);
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
mutex_lock(&kvm->slots_lock);
list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) {
bool wildcard = !(args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH);
if (p->eventfd != eventfd ||
p->addr != args->addr ||
p->length != args->len ||
p->wildcard != wildcard)
continue;
if (!p->wildcard && p->datamatch != args->datamatch)
continue;
kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
ioeventfd_release(p);
ret = 0;
break;
}
mutex_unlock(&kvm->slots_lock);
eventfd_ctx_put(eventfd);
return ret;
}
int
kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN)
return kvm_deassign_ioeventfd(kvm, args);
return kvm_assign_ioeventfd(kvm, args);
}