[RFC PATCH 03/34] KVM: irqfd: Allow KVM backends to override IRQ injection via set_irq callback

[Karim Manaouil]

Some KVM backends, such as Gunyah, require custom mechanisms to inject
interrupts into the guest. For example, Gunyah performs IRQ injection
through a hypercall to the underlying hypervisor.

To support such use case, this patch introduces a new optional callback
field `set_irq` in `struct kvm_kernel_irqfd`. If this callback is set,
irqfd injection will use the provided function instead of calling
kvm_set_irq() directly.

The default behavior is unchanged for existing users that do not override
the `set_irq` field.

Signed-off-by: Karim Manaouil <karim.manaouil at linaro.org>
---
 include/linux/kvm_irqfd.h | 1 +
 virt/kvm/eventfd.c        | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h
index e8d21d443c58..7d54bc12c4bf 100644
--- a/include/linux/kvm_irqfd.h
+++ b/include/linux/kvm_irqfd.h
@@ -46,6 +46,7 @@ struct kvm_kernel_irqfd {
 	/* Used for level IRQ fast-path */
 	int gsi;
 	struct work_struct inject;
+	int (*set_irq)(struct kvm_kernel_irqfd *);
 	/* The resampler used by this irqfd (resampler-only) */
 	struct kvm_kernel_irqfd_resampler *resampler;
 	/* Eventfd notified on resample (resampler-only) */
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 5f3776a1b960..d6702225e7f2 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -63,6 +63,11 @@ irqfd_inject(struct work_struct *work)
 		container_of(work, struct kvm_kernel_irqfd, inject);
 	struct kvm *kvm = irqfd->kvm;
 
+	if (irqfd->set_irq) {
+		irqfd->set_irq(irqfd);
+		return;
+	}
+
 	if (!irqfd->resampler) {
 		kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1,
 				false);
-- 
2.39.5