[KVM PATCH v7 2/3] kvm: add support for irqfd via eventfd-notification interface

Gregory Haskins
2009-05-12T18:27:56Z

KVM provides a complete virtual system environment for guests, including
support for injecting interrupts modeled after the real exception/interrupt
facilities present on the native platform (such as the IDT on x86).
Virtual interrupts can come from a variety of sources (emulated devices,
pass-through devices, etc) but all must be injected to the guest via
the KVM infrastructure. This patch adds a new mechanism to inject a specific
interrupt to a guest using a decoupled eventfd mechnanism: Any legal signal
on the irqfd (using eventfd semantics from either userspace or kernel) will
translate into an injected interrupt in the guest at the next available
interrupt window.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

arch/x86/kvm/Makefile | 2
arch/x86/kvm/x86.c | 1
include/linux/kvm.h | 10 ++
include/linux/kvm_host.h | 5 +
virt/kvm/eventfd.c | 187 ++++++++++++++++++++++++++++++++++++++++++++++
virt/kvm/kvm_main.c | 20 +++++
6 files changed, 224 insertions(+), 1 deletions(-)
create mode 100644 virt/kvm/eventfd.c

diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index b43c4ef..4d50904 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -3,7 +3,7 @@
#

common-objs = $(addprefix ../../../virt/kvm/, kvm_main.o ioapic.o \
- coalesced_mmio.o irq_comm.o)
+ coalesced_mmio.o irq_comm.o eventfd.o)
ifeq ($(CONFIG_KVM_TRACE),y)
common-objs += $(addprefix ../../../virt/kvm/, kvm_trace.o)
endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fd0a571..ba541f6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1026,6 +1026,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_REINJECT_CONTROL:
case KVM_CAP_IRQ_INJECT_STATUS:
case KVM_CAP_ASSIGN_DEV_IRQ:
+ case KVM_CAP_EVENTFD:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 3db5d8d..dfc4bcc 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -415,6 +415,7 @@ struct kvm_trace_rec {
#define KVM_CAP_ASSIGN_DEV_IRQ 29
/* Another bug in KVM_SET_USER_MEMORY_REGION fixed: */
#define KVM_CAP_JOIN_MEMORY_REGIONS_WORKS 30
+#define KVM_CAP_EVENTFD 31

#ifdef KVM_CAP_IRQ_ROUTING

@@ -454,6 +455,13 @@ struct kvm_irq_routing {

#endif

+struct kvm_irqfd {
+ __u32 fd;
+ __u32 gsi;
+ __u32 flags;
+ __u8 pad[20];
+};
+
/*
* ioctls for VM fds
*/
@@ -498,6 +506,8 @@ struct kvm_irq_routing {
#define KVM_ASSIGN_SET_MSIX_ENTRY \
_IOW(KVMIO, 0x74, struct kvm_assigned_msix_entry)
#define KVM_DEASSIGN_DEV_IRQ _IOW(KVMIO, 0x75, struct kvm_assigned_irq)
+#define KVM_ASSIGN_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd)
+#define KVM_DEASSIGN_IRQFD _IOW(KVMIO, 0x77, __u32)

/*
* ioctls for vcpu fds
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2b8df0c..1acc528 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -134,6 +134,7 @@ struct kvm {
struct list_head vm_list;
struct kvm_io_bus mmio_bus;
struct kvm_io_bus pio_bus;
+ struct list_head irqfds;
struct kvm_vm_stat stat;
struct kvm_arch arch;
atomic_t users_count;
@@ -525,4 +526,8 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {}

#endif

+int kvm_assign_irqfd(struct kvm *kvm, int fd, int gsi, int flags);
+int kvm_deassign_irqfd(struct kvm *kvm, int fd);
+void kvm_irqfd_release(struct kvm *kvm);
+
#endif
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
new file mode 100644
index 0000000..71afd62
--- /dev/null
+++ b/virt/kvm/eventfd.c
@@ -0,0 +1,187 @@
+/*
+ * kvm eventfd support - use eventfd objects to signal various KVM events
+ *
+ * Copyright 2009 Novell. All Rights Reserved.
+ *
+ * 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/workqueue.h>
+#include <linux/syscalls.h>
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/file.h>
+#include <linux/list.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 {
+ struct kvm *kvm;
+ int gsi;
+ int fd;
+ struct file *file;
+ struct list_head list;
+ poll_table pt;
+ wait_queue_head_t *wqh;
+ wait_queue_t wait;
+ struct work_struct work;
+};
+
+static void
+irqfd_inject(struct work_struct *work)
+{
+ struct _irqfd *irqfd = container_of(work, struct _irqfd, work);
+ struct kvm *kvm = irqfd->kvm;
+
+ mutex_lock(&kvm->lock);
+ kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
+ kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
+ mutex_unlock(&kvm->lock);
+}
+
+static int
+irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
+
+ /*
+ * The wake_up with interrupts disabled. Therefore we need to defer
+ * the IRQ injection until later since we need to acquire the
+ * kvm->lock to do so.
+ */
+ schedule_work(&irqfd->work);
+
+ 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);
+
+ irqfd->wqh = wqh;
+ add_wait_queue(wqh, &irqfd->wait);
+}
+
+int
+kvm_assign_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
+{
+ struct _irqfd *irqfd;
+ struct file *file = NULL;
+ int ret;
+
+ irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
+ if (!irqfd)
+ return -ENOMEM;
+
+ irqfd->kvm = kvm;
+ irqfd->gsi = gsi;
+ irqfd->fd = fd;
+ INIT_LIST_HEAD(&irqfd->list);
+ INIT_WORK(&irqfd->work, irqfd_inject);
+
+ /*
+ * Embed the file* lifetime in the irqfd.
+ */
+ file = fget(fd);
+ if (IS_ERR(file)) {
+ ret = PTR_ERR(file);
+ goto fail;
+ }
+
+ /*
+ * 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);
+
+ ret = file->f_op->poll(file, &irqfd->pt);
+ if (ret < 0)
+ goto fail;
+
+ irqfd->file = file;
+
+ mutex_lock(&kvm->lock);
+ list_add_tail(&irqfd->list, &kvm->irqfds);
+ mutex_unlock(&kvm->lock);
+
+ return 0;
+
+fail:
+ if (irqfd->wqh)
+ remove_wait_queue(irqfd->wqh, &irqfd->wait);
+
+ if (file && !IS_ERR(file))
+ fput(file);
+
+ kfree(irqfd);
+ return ret;
+}
+
+static void
+irqfd_release(struct _irqfd *irqfd)
+{
+ remove_wait_queue(irqfd->wqh, &irqfd->wait);
+
+ flush_work(&irqfd->work);
+ fput(irqfd->file);
+
+ list_del(&irqfd->list);
+ kfree(irqfd);
+}
+
+int
+kvm_deassign_irqfd(struct kvm *kvm, int fd)
+{
+ struct _irqfd *irqfd, *tmp;
+
+ mutex_lock(&kvm->lock);
+
+ /*
+ * linear search isn't brilliant, but this should be a infrequent
+ * operation and the list should not grow very large
+ */
+ list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds, list) {
+ if (irqfd->fd != fd)
+ continue;
+
+ irqfd_release(irqfd);
+ mutex_unlock(&kvm->lock);
+ return 0;
+ }
+ mutex_unlock(&kvm->lock);
+
+ return -ENOENT;
+}
+
+void
+kvm_irqfd_release(struct kvm *kvm)
+{
+ struct _irqfd *irqfd, *tmp;
+
+ /* don't bother with the lock..we are shutting down */
+ list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds, list)
+ irqfd_release(irqfd);
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4d00942..7aa9f0a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -983,6 +983,7 @@ static struct kvm *kvm_create_vm(void)
atomic_inc(&kvm->mm->mm_count);
spin_lock_init(&kvm->mmu_lock);
kvm_io_bus_init(&kvm->pio_bus);
+ INIT_LIST_HEAD(&kvm->irqfds);
mutex_init(&kvm->lock);
kvm_io_bus_init(&kvm->mmio_bus);
init_rwsem(&kvm->slots_lock);
@@ -1034,6 +1035,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
spin_lock(&kvm_lock);
list_del(&kvm->vm_list);
spin_unlock(&kvm_lock);
+ kvm_irqfd_release(kvm);
kvm_free_irq_routing(kvm);
kvm_io_bus_destroy(&kvm->pio_bus);
kvm_io_bus_destroy(&kvm->mmio_bus);
@@ -2208,6 +2210,24 @@ static long kvm_vm_ioctl(struct file *filp,
}
#endif
#endif /* KVM_CAP_IRQ_ROUTING */
+ case KVM_ASSIGN_IRQFD: {
+ struct kvm_irqfd data;
+
+ r = -EFAULT;
+ if (copy_from_user(&data, argp, sizeof data))
+ goto out;
+ r = kvm_assign_irqfd(kvm, data.fd, data.gsi, data.flags);
+ break;
+ }
+ case KVM_DEASSIGN_IRQFD: {
+ u32 data;
+
+ r = -EFAULT;
+ if (copy_from_user(&data, argp, sizeof data))
+ goto out;
+ r = kvm_deassign_irqfd(kvm, data);
+ break;
+ }
default:
r = kvm_arch_vm_ioctl(filp, ioctl, arg);
}