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    SubjectRe: [KVM PATCH v9] kvm: add support for irqfd
    Gregory Haskins wrote:
    > (This is v9, applies to kvm.git:2ffc3882)
    >
    > 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.
    >
    > [ Changelog:
    >
    > v9:
    > *) Fixed a bug in deassign where we could deadlock with the way
    > flush_work was being used (Thanks to Marcelo Tosatti's for spotting
    > this bug).
    > *) Rebased to kvm.git:2ffc3882
    >
    > v8:
    > *) Re-seperated irqfd and iofd (now called iosignalfd) into two
    > distinct series.
    > *) We compare both the fd/file and gsi on deassign
    > *) De-assign is exhaustive (to support multiple associations in the
    > future)
    > *) s/KVM_CAP_EVENTFD/KVM_CAP_IRQFD
    >
    > v7:
    > *) Added "iofd" to allow PIO/MMIO writes to generate an eventfd
    > signal. This was previously discussed as "hypercallfd", but
    > since explicit hypercalls are not looking to be very popular,
    > and based on the fact that they were not going to carry payload
    > anyway, I named them "iofd".
    > *) Generalized some of the code so that irqfd and iofd could be
    > logically grouped together. For instance
    > s/KVM_CAP_IRQFD/KVM_CAP_EVENTFD and virt/kvm/irqfd.c becomes
    > virt/kvm/eventfd.c
    > *) Added support for "deassign" operations to ensure we can properly
    > support hot-unplug.
    > *) Reinstated the eventfd EXPORT_SYMBOL patch since we need it again
    > for supporting iofd.
    > *) Rebased to kvm.git:b5e725fa
    >
    > v6:
    > *) Moved eventfd creation back to userspace, per Avi's request
    > *) Dropped no longer necessary supporting patches from series
    > *) Rebased to kvm.git:833367b57
    >
    > v5:
    > *) Added padding to the ioctl structure
    > *) Added proper ref-count increment to the file before returning
    > success. (Needs review by Al Viro, Davide Libenzi)
    > *) Cleaned up error-handling path to make sure we remove ourself
    > from the waitq if necessary.
    > *) Make sure we only add ourselves to kvm->irqfds if successful
    > creating the irqfd in the first place.
    > *) Rebased to kvm.git:66b0aed4
    >
    > v4:
    > *) Changed allocation model to create the new fd last, after
    > we get past the last potential error point by using Davide's
    > new eventfd_file_create interface (Al Viro, Davide Libenzi)
    > *) We no longer export sys_eventfd2() since it is replaced
    > functionally with eventfd_file_create();
    > *) Rebased to kvm.git:7da2e3ba
    >
    > v3:
    > *) The kernel now allocates the eventfd (need to export sys_eventfd2)
    > *) Added a flags field for future expansion to kvm_irqfd()
    > *) We properly toggle the irq level 1+0.
    > *) We re-use the USERSPACE_SRC_ID instead of creating our own
    > *) Properly check for failures establishing a poll-table with eventfd
    > *) Fixed fd/file leaks on failure
    > *) Rebased to lateste kvm.git::41b76d8d04
    >
    > v2:
    > *) Dropped notifier_chain based callbacks in favor of
    > wait_queue_t::func and file::poll based callbacks (Thanks to
    > Davide for the suggestion)
    >
    > v1:
    > *) Initial release
    >
    > ]
    >
    > Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    > ---
    >
    > arch/x86/kvm/Makefile | 2
    > arch/x86/kvm/x86.c | 1
    > include/linux/kvm.h | 11 ++
    > include/linux/kvm_host.h | 4 +
    > virt/kvm/eventfd.c | 224 ++++++++++++++++++++++++++++++++++++++++++++++
    > virt/kvm/kvm_main.c | 11 ++
    > 6 files changed, 252 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 44e87a5..123e833 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_IRQFD:
    > r = 1;
    > break;
    > case KVM_CAP_COALESCED_MMIO:
    > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
    > index 3db5d8d..a1ecc6a 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_IRQFD 31
    >
    > #ifdef KVM_CAP_IRQ_ROUTING
    >
    > @@ -454,6 +455,15 @@ struct kvm_irq_routing {
    >
    > #endif
    >
    > +#define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
    > +
    > +struct kvm_irqfd {
    > + __u32 fd;
    > + __u32 gsi;
    > + __u32 flags;
    > + __u8 pad[20];
    > +};
    > +
    > /*
    > * ioctls for VM fds
    > */
    > @@ -498,6 +508,7 @@ 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_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd)
    >
    > /*
    > * ioctls for vcpu fds
    > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > index 8f410d3..3b6caf5 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;
    > @@ -528,4 +529,7 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {}
    >
    > #endif
    >
    > +int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags);
    > +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..41897f9
    > --- /dev/null
    > +++ b/virt/kvm/eventfd.c
    > @@ -0,0 +1,224 @@
    > +/*
    > + * 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;
    > + 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);
    > +}
    > +
    > +static int
    > +kvm_assign_irqfd(struct kvm *kvm, int fd, int gsi)
    > +{
    > + 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;
    > + 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)
    > +{
    > + /*
    > + * The ordering is important. We must remove ourselves from the wqh
    > + * first to ensure no more event callbacks are issued, and then flush
    > + * any previously scheduled work prior to freeing the memory
    > + */
    > + remove_wait_queue(irqfd->wqh, &irqfd->wait);
    > +
    > + flush_work(&irqfd->work);
    > +
    > + fput(irqfd->file);
    > + kfree(irqfd);
    > +}
    > +
    > +static struct _irqfd *irqfd_remove(struct kvm *kvm, struct file *file, int gsi)
    >

    Grr.. just noticed a sloppy style inconsistency.

    Avi, if you end up liking v9, please put a CR between the return-type
    and function-name before applying it so its consistent with the rest of
    my code. Otherwise, I will include that change in v10, if we need it.

    > +{
    > + struct _irqfd *irqfd;
    > +
    > + 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(irqfd, &kvm->irqfds, list) {
    > + if (irqfd->file != file || irqfd->gsi != gsi)
    > + continue;
    > +
    > + list_del(&irqfd->list);
    > + mutex_unlock(&kvm->lock);
    > +
    > + return irqfd;
    > + }
    > +
    > + mutex_unlock(&kvm->lock);
    > +
    > + return NULL;
    > +}
    > +
    > +static int
    > +kvm_deassign_irqfd(struct kvm *kvm, int fd, int gsi)
    > +{
    > + struct _irqfd *irqfd;
    > + struct file *file;
    > +
    > + file = fget(fd);
    > + if (IS_ERR(file))
    > + return PTR_ERR(file);
    > +
    > + while ((irqfd = irqfd_remove(kvm, file, gsi)))
    > + /*
    > + * We remove the item from the list under the lock, but we
    > + * free it outside the lock to avoid deadlocking with the
    > + * flush_work and the work_item taking the lock
    > + */
    > + irqfd_release(irqfd);
    > +
    > + fput(file);
    > +
    > + return -ENOENT;
    > +}
    > +
    > +int
    > +kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
    > +{
    > + if (flags & KVM_IRQFD_FLAG_DEASSIGN)
    > + return kvm_deassign_irqfd(kvm, fd, gsi);
    > +
    > + return kvm_assign_irqfd(kvm, fd, gsi);
    > +}
    > +
    > +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) {
    > + list_del(&irqfd->list);
    > + irqfd_release(irqfd);
    > + }
    > +}
    > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    > index bebfe59..b58837d 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);
    > @@ -2210,6 +2212,15 @@ static long kvm_vm_ioctl(struct file *filp,
    > }
    > #endif
    > #endif /* KVM_CAP_IRQ_ROUTING */
    > + case KVM_IRQFD: {
    > + struct kvm_irqfd data;
    > +
    > + r = -EFAULT;
    > + if (copy_from_user(&data, argp, sizeof data))
    > + goto out;
    > + r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags);
    > + break;
    > + }
    > default:
    > r = kvm_arch_vm_ioctl(filp, ioctl, arg);
    > }
    >
    > --
    > To unsubscribe from this list: send the line "unsubscribe kvm" in
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    >


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