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    Subject[PATCH v4 1/3] kvm: Extend irqfd to support level interrupts
    Date
    In order to inject a level interrupt from an external source using an
    irqfd, we need to allocate a new irq_source_id. This allows us to
    assert and (later) de-assert an interrupt line independently from
    users of KVM_IRQ_LINE and avoid lost interrupts.

    We also add what may appear like a bit of excessive infrastructure
    around an object for storing this irq_source_id. However, notice
    that we only provide a way to assert the interrupt here. A follow-on
    interface will make use of the same irq_source_id to allow de-assert.

    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    ---

    Documentation/virtual/kvm/api.txt | 6 ++
    arch/x86/kvm/x86.c | 1
    include/linux/kvm.h | 3 +
    virt/kvm/eventfd.c | 114 ++++++++++++++++++++++++++++++++++++-
    4 files changed, 120 insertions(+), 4 deletions(-)

    diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
    index 100acde..c7267d5 100644
    --- a/Documentation/virtual/kvm/api.txt
    +++ b/Documentation/virtual/kvm/api.txt
    @@ -1981,6 +1981,12 @@ the guest using the specified gsi pin. The irqfd is removed using
    the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
    and kvm_irqfd.gsi.

    +The KVM_IRQFD_FLAG_LEVEL flag indicates the gsi input is for a level
    +triggered interrupt. In this case a new irqchip input is allocated
    +which is logically OR'd with other inputs allowing multiple sources
    +to independently assert level interrupts. The KVM_IRQFD_FLAG_LEVEL
    +is only necessary on setup, teardown is identical to that above.
    +KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.

    5. The kvm_run structure
    ------------------------
    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index a01a424..80bed07 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -2148,6 +2148,7 @@ int kvm_dev_ioctl_check_extension(long ext)
    case KVM_CAP_GET_TSC_KHZ:
    case KVM_CAP_PCI_2_3:
    case KVM_CAP_KVMCLOCK_CTRL:
    + case KVM_CAP_IRQFD_LEVEL:
    r = 1;
    break;
    case KVM_CAP_COALESCED_MMIO:
    diff --git a/include/linux/kvm.h b/include/linux/kvm.h
    index 2ce09aa..b2e6e4f 100644
    --- a/include/linux/kvm.h
    +++ b/include/linux/kvm.h
    @@ -618,6 +618,7 @@ struct kvm_ppc_smmu_info {
    #define KVM_CAP_PPC_GET_SMMU_INFO 78
    #define KVM_CAP_S390_COW 79
    #define KVM_CAP_PPC_ALLOC_HTAB 80
    +#define KVM_CAP_IRQFD_LEVEL 81

    #ifdef KVM_CAP_IRQ_ROUTING

    @@ -683,6 +684,8 @@ struct kvm_xen_hvm_config {
    #endif

    #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
    +/* Available with KVM_CAP_IRQFD_LEVEL */
    +#define KVM_IRQFD_FLAG_LEVEL (1 << 1)

    struct kvm_irqfd {
    __u32 fd;
    diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
    index 7d7e2aa..ecdbfea 100644
    --- a/virt/kvm/eventfd.c
    +++ b/virt/kvm/eventfd.c
    @@ -36,6 +36,68 @@
    #include "iodev.h"

    /*
    + * An irq_source_id can be created from KVM_IRQFD for level interrupt
    + * injections and shared with other interfaces for EOI or de-assert.
    + * Create an object with reference counting to make it easy to use.
    + */
    +struct _irq_source {
    + int id; /* the IRQ source ID */
    + bool level_asserted; /* Track assertion state and protect with lock */
    + spinlock_t lock; /* to avoid unnecessary re-assert/spurious eoi. */
    + struct kvm *kvm;
    + struct kref kref;
    +};
    +
    +static void _irq_source_release(struct kref *kref)
    +{
    + struct _irq_source *source;
    +
    + source = container_of(kref, struct _irq_source, kref);
    +
    + /* This also de-asserts */
    + kvm_free_irq_source_id(source->kvm, source->id);
    + kfree(source);
    +}
    +
    +static void _irq_source_put(struct _irq_source *source)
    +{
    + if (source)
    + kref_put(&source->kref, _irq_source_release);
    +}
    +
    +static struct _irq_source *__attribute__ ((used)) /* white lie for now */
    +_irq_source_get(struct _irq_source *source)
    +{
    + if (source)
    + kref_get(&source->kref);
    +
    + return source;
    +}
    +
    +static struct _irq_source *_irq_source_alloc(struct kvm *kvm)
    +{
    + struct _irq_source *source;
    + int id;
    +
    + source = kzalloc(sizeof(*source), GFP_KERNEL);
    + if (!source)
    + return ERR_PTR(-ENOMEM);
    +
    + id = kvm_request_irq_source_id(kvm);
    + if (id < 0) {
    + kfree(source);
    + return ERR_PTR(id);
    + }
    +
    + kref_init(&source->kref);
    + spin_lock_init(&source->lock);
    + source->kvm = kvm;
    + source->id = id;
    +
    + return source;
    +}
    +
    +/*
    * --------------------------------------------------------------------
    * irqfd: Allows an fd to be used to inject an interrupt to the guest
    *
    @@ -52,6 +114,8 @@ struct _irqfd {
    /* Used for level IRQ fast-path */
    int gsi;
    struct work_struct inject;
    + /* IRQ source ID for level triggered irqfds */
    + struct _irq_source *source;
    /* Used for setup/shutdown */
    struct eventfd_ctx *eventfd;
    struct list_head list;
    @@ -62,7 +126,7 @@ struct _irqfd {
    static struct workqueue_struct *irqfd_cleanup_wq;

    static void
    -irqfd_inject(struct work_struct *work)
    +irqfd_inject_edge(struct work_struct *work)
    {
    struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
    struct kvm *kvm = irqfd->kvm;
    @@ -71,6 +135,29 @@ irqfd_inject(struct work_struct *work)
    kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
    }

    +static void
    +irqfd_inject_level(struct work_struct *work)
    +{
    + struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
    +
    + /*
    + * Inject an interrupt only if not already asserted.
    + *
    + * We can safely ignore the kvm_set_irq return value here. If
    + * masked, the irr bit is still set and will eventually be serviced.
    + * This interface does not guarantee immediate injection. If
    + * coalesced, an eoi will be coming where we can de-assert and
    + * re-inject if necessary. NB, if you need to know if an interrupt
    + * was coalesced, this interface is not for you.
    + */
    + spin_lock(&irqfd->source->lock);
    + if (!irqfd->source->level_asserted) {
    + kvm_set_irq(irqfd->kvm, irqfd->source->id, irqfd->gsi, 1);
    + irqfd->source->level_asserted = true;
    + }
    + spin_unlock(&irqfd->source->lock);
    +}
    +
    /*
    * Race-free decouple logic (ordering is critical)
    */
    @@ -96,6 +183,9 @@ irqfd_shutdown(struct work_struct *work)
    * It is now safe to release the object's resources
    */
    eventfd_ctx_put(irqfd->eventfd);
    +
    + _irq_source_put(irqfd->source);
    +
    kfree(irqfd);
    }

    @@ -202,6 +292,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
    {
    struct kvm_irq_routing_table *irq_rt;
    struct _irqfd *irqfd, *tmp;
    + struct _irq_source *source = NULL;
    struct file *file = NULL;
    struct eventfd_ctx *eventfd = NULL;
    int ret;
    @@ -214,7 +305,19 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
    irqfd->kvm = kvm;
    irqfd->gsi = args->gsi;
    INIT_LIST_HEAD(&irqfd->list);
    - INIT_WORK(&irqfd->inject, irqfd_inject);
    +
    + if (args->flags & KVM_IRQFD_FLAG_LEVEL) {
    + source = _irq_source_alloc(kvm);
    + if (IS_ERR(source)) {
    + ret = PTR_ERR(source);
    + goto fail;
    + }
    +
    + irqfd->source = source;
    + INIT_WORK(&irqfd->inject, irqfd_inject_level);
    + } else
    + INIT_WORK(&irqfd->inject, irqfd_inject_edge);
    +
    INIT_WORK(&irqfd->shutdown, irqfd_shutdown);

    file = eventfd_fget(args->fd);
    @@ -276,10 +379,13 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
    return 0;

    fail:
    + if (source && !IS_ERR(source))
    + _irq_source_put(source);
    +
    if (eventfd && !IS_ERR(eventfd))
    eventfd_ctx_put(eventfd);

    - if (!IS_ERR(file))
    + if (file && !IS_ERR(file))
    fput(file);

    kfree(irqfd);
    @@ -340,7 +446,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
    int
    kvm_irqfd(struct kvm *kvm, struct kvm_irqfd *args)
    {
    - if (args->flags & ~KVM_IRQFD_FLAG_DEASSIGN)
    + if (args->flags & ~(KVM_IRQFD_FLAG_DEASSIGN | KVM_IRQFD_FLAG_LEVEL))
    return -EINVAL;

    if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)


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