linux-kernel - [RFC PATCH 02/34] KVM: irqfd: Add architecture hooks for irqfd allocation and initialization

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Message-Id: <20250424141341.841734-3-karim.manaouil@linaro.org>
Date: Thu, 24 Apr 2025 15:13:09 +0100
From: Karim Manaouil <karim.manaouil@...aro.org>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev
Cc: Karim Manaouil <karim.manaouil@...aro.org>,
	Alexander Graf <graf@...zon.com>,
	Alex Elder <elder@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Fuad Tabba <tabba@...gle.com>,
	Joey Gouly <joey.gouly@....com>,
	Jonathan Corbet <corbet@....net>,
	Marc Zyngier <maz@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
	Quentin Perret <qperret@...gle.com>,
	Rob Herring <robh@...nel.org>,
	Srinivas Kandagatla <srini@...nel.org>,
	Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
	Will Deacon <will@...nel.org>,
	Haripranesh S <haripran@....qualcomm.com>,
	Carl van Schaik <cvanscha@....qualcomm.com>,
	Murali Nalajala <mnalajal@...cinc.com>,
	Sreenivasulu Chalamcharla <sreeniva@....qualcomm.com>,
	Trilok Soni <tsoni@...cinc.com>,
	Stefan Schmidt <stefan.schmidt@...aro.org>
Subject: [RFC PATCH 02/34] KVM: irqfd: Add architecture hooks for irqfd allocation and initialization

Some KVM backends, such as Gunyah, require irqfd structures to carry
platform-specific state or setup logic. To support these use cases,
introduce three weakly-defined functions:

  - kvm_arch_irqfd_alloc()
  - kvm_arch_irqfd_free()
  - kvm_arch_irqfd_init()

These allow KVM backends to override irqfd allocation, teardown,
and initialization logic. The default implementations simply
allocate/finalize a standard `struct kvm_kernel_irqfd`, maintaining
existing behaviour.

This change is required by the Gunyah backend, which uses these hooks
to associate irqfd objects with Gunyah-specific bell resource handles
for IRQ injection via hypercalls.

Signed-off-by: Karim Manaouil <karim.manaouil@...aro.org>
---
 include/linux/kvm_irqfd.h |  4 ++++
 virt/kvm/eventfd.c        | 31 ++++++++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h
index 8ad43692e3bb..e8d21d443c58 100644
--- a/include/linux/kvm_irqfd.h
+++ b/include/linux/kvm_irqfd.h
@@ -61,4 +61,8 @@ struct kvm_kernel_irqfd {
 	struct irq_bypass_producer *producer;
 };
 
+struct kvm_kernel_irqfd *kvm_arch_irqfd_alloc(void);
+void kvm_arch_irqfd_free(struct kvm_kernel_irqfd *irqfd);
+int kvm_arch_irqfd_init(struct kvm_kernel_irqfd *irqfd);
+
 #endif /* __LINUX_KVM_IRQFD_H */
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 11e5d1e3f12e..5f3776a1b960 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -32,6 +32,24 @@
 
 static struct workqueue_struct *irqfd_cleanup_wq;
 
+struct kvm_kernel_irqfd __attribute__((weak))
+*kvm_arch_irqfd_alloc(void)
+{
+	return kzalloc(sizeof(struct kvm_kernel_irqfd), GFP_KERNEL_ACCOUNT);
+}
+
+void __attribute__((weak))
+kvm_arch_irqfd_free(struct kvm_kernel_irqfd *irqfd)
+{
+	kfree(irqfd);
+}
+
+int __attribute__((weak))
+kvm_arch_irqfd_init(struct kvm_kernel_irqfd *irqfd)
+{
+	return 0;
+}
+
 bool __attribute__((weak))
 kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args)
 {
@@ -153,7 +171,7 @@ irqfd_shutdown(struct work_struct *work)
 	irq_bypass_unregister_consumer(&irqfd->consumer);
 #endif
 	eventfd_ctx_put(irqfd->eventfd);
-	kfree(irqfd);
+	kvm_arch_irqfd_free(irqfd);
 }
 
 
@@ -315,7 +333,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	if (!kvm_arch_irqfd_allowed(kvm, args))
 		return -EINVAL;
 
-	irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL_ACCOUNT);
+	irqfd = kvm_arch_irqfd_alloc();
 	if (!irqfd)
 		return -ENOMEM;
 
@@ -396,6 +414,13 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
 	init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
 
+	/*
+	 * Give a chance to archiectures to finish initilization.
+	 * E.g. Gunyah needs to register a resource ticket for this irq.
+	 */
+	if (kvm_arch_irqfd_init(irqfd))
+		goto fail;
+
 	spin_lock_irq(&kvm->irqfds.lock);
 
 	ret = 0;
@@ -452,7 +477,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 		eventfd_ctx_put(eventfd);
 
 out:
-	kfree(irqfd);
+	kvm_arch_irqfd_free(irqfd);
 	return ret;
 }
 
-- 
2.39.5