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    SubjectRe: [KVM PATCH v2 1/2] KVM: export lockless GSI attribute
    Gregory Haskins wrote:
    > Certain GSI's support lockless injecton, but we have no way to detect
    > which ones at the GSI level. Knowledge of this attribute will be
    > useful later in the series so that we can optimize irqfd injection
    > paths for cases where we know the code will not sleep. Therefore,
    > we provide an API to query a specific GSI.
    >
    > Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    > ---
    >
    > include/linux/kvm_host.h | 2 ++
    > virt/kvm/irq_comm.c | 19 +++++++++++++++++++
    > 2 files changed, 21 insertions(+), 0 deletions(-)
    >
    > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > index bd5a616..93393a4 100644
    > --- a/include/linux/kvm_host.h
    > +++ b/include/linux/kvm_host.h
    > @@ -119,6 +119,7 @@ struct kvm_memory_slot {
    > struct kvm_kernel_irq_routing_entry {
    > u32 gsi;
    > u32 type;
    > + bool lockless;
    > int (*set)(struct kvm_kernel_irq_routing_entry *e,
    > struct kvm *kvm, int irq_source_id, int level);
    > union {
    > @@ -417,6 +418,7 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
    > unsigned long *deliver_bitmask);
    > #endif
    > int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
    > +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq);
    > void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
    > void kvm_register_irq_ack_notifier(struct kvm *kvm,
    > struct kvm_irq_ack_notifier *kian);
    > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
    > index 00c68d2..04f0134 100644
    > --- a/virt/kvm/irq_comm.c
    > +++ b/virt/kvm/irq_comm.c
    > @@ -174,6 +174,23 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
    > return ret;
    > }
    >
    > +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq)
    > +{
    > + struct kvm_kernel_irq_routing_entry *e;
    > + struct kvm_irq_routing_table *irq_rt;
    > + struct hlist_node *n;
    > + int ret = -ENOENT;
    > +
    > + rcu_read_lock();
    > + irq_rt = rcu_dereference(kvm->irq_routing);
    > + if (irq < irq_rt->nr_rt_entries)
    > + hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
    > + ret = e->lockless ? 1 : 0;

    Sigh... just noticed this as it hits the list. I should probably break
    out of the loop here.

    > + rcu_read_unlock();
    > +
    > + return ret;
    > +}
    > +
    > void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
    > {
    > struct kvm_irq_ack_notifier *kian;
    > @@ -314,6 +331,7 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
    >
    > e->gsi = ue->gsi;
    > e->type = ue->type;
    > + e->lockless = false;
    > switch (ue->type) {
    > case KVM_IRQ_ROUTING_IRQCHIP:
    > delta = 0;
    > @@ -342,6 +360,7 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
    > e->msi.address_lo = ue->u.msi.address_lo;
    > e->msi.address_hi = ue->u.msi.address_hi;
    > e->msi.data = ue->u.msi.data;
    > + e->lockless = true;
    > break;
    > default:
    > goto out;
    >
    > --
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