linux-kernel - [RFC PATCH 33/34] KVM: gunyah: Implement irqfd interface

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Message-Id: <20250424141341.841734-34-karim.manaouil@linaro.org>
Date: Thu, 24 Apr 2025 15:13:40 +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 33/34] KVM: gunyah: Implement irqfd interface

Enables support for injecting interrupts into guest vCPUs via KVM's
irqfd interface. Irqfds are requested from userspace via KVM_IRQFD
ioctl. kvm_arch_irqfd_init() implementation, in Gunyah, then creates
a resource ticket for the irqfd. The userspace must also create a
devicetree node to create a doorbell with the corresponding label.
Later after VM configuration (in gunyah_vm_start()), the resource ticket
will be populated and the irqfd instance will be bound to its
corresponding doorbell (identified with a capability id). When userspace
asserts the irq line, irqfd->set_irq() callback is called to inject an
interrupt into the guest via a hypercall.

Signed-off-by: Karim Manaouil <karim.manaouil@...aro.org>
---
 arch/arm64/kvm/gunyah.c | 100 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/arch/arm64/kvm/gunyah.c b/arch/arm64/kvm/gunyah.c
index df922be2429e..23b9128bf5b1 100644
--- a/arch/arm64/kvm/gunyah.c
+++ b/arch/arm64/kvm/gunyah.c
@@ -29,6 +29,14 @@
 #define WRITE_TAG (1 << 0)
 #define SHARE_TAG (1 << 1)
 
+struct gunyah_irqfd {
+	struct gunyah_vm *ghvm;
+	struct gunyah_resource *ghrsc;
+	struct gunyah_vm_resource_ticket ticket;
+	struct kvm_kernel_irqfd irqfd;
+	bool level;
+};
+
 static int gunyah_vm_start(struct gunyah_vm *ghvm);
 
 static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
@@ -852,6 +860,98 @@ static int gunyah_start_paging(struct gunyah_vm *ghvm)
 	return ret;
 }
 
+static bool gunyah_irqfd_populate(struct gunyah_vm_resource_ticket *ticket,
+				  struct gunyah_resource *ghrsc)
+{
+	struct gunyah_irqfd *irqfd =
+		container_of(ticket, struct gunyah_irqfd, ticket);
+	int ret;
+
+	if (irqfd->ghrsc) {
+		pr_warn("irqfd%d already got a Gunyah resource", irqfd->ticket.label);
+		return false;
+	}
+
+	irqfd->ghrsc = ghrsc;
+	if (irqfd->level) {
+		/* Configure the bell to trigger when bit 0 is asserted (see
+		 * irq_wakeup) and for bell to automatically clear bit 0 once
+		 * received by the VM (ack_mask).  need to make sure bit 0 is cleared right away,
+		 * otherwise the line will never be deasserted. Emulating edge
+		 * trigger interrupt does not need to set either mask
+		 * because irq is listed only once per gunyah_hypercall_bell_send
+		 */
+		ret = gunyah_hypercall_bell_set_mask(irqfd->ghrsc->capid, 1, 1);
+		if (ret)
+			pr_warn("irq %d couldn't be set as level triggered."
+				"Might cause IRQ storm if asserted\n",
+				irqfd->ticket.label);
+	}
+
+	return true;
+}
+
+static void gunyah_irqfd_unpopulate(struct gunyah_vm_resource_ticket *ticket,
+				    struct gunyah_resource *ghrsc)
+{
+}
+
+static int gunyah_set_irq(struct kvm_kernel_irqfd *kvm_irqfd)
+{
+	int ret;
+	struct gunyah_irqfd *irqfd =
+		container_of(kvm_irqfd, struct gunyah_irqfd, irqfd);
+
+	if (irqfd->ghrsc) {
+		if (gunyah_hypercall_bell_send(irqfd->ghrsc->capid, 1, NULL)) {
+			pr_err_ratelimited("Failed to inject interrupt %d: %d\n",
+					irqfd->ticket.label, ret);
+			return -1;
+		}
+	} else {
+		pr_err_ratelimited("Premature injection of interrupt\n");
+		return -1;
+	}
+
+	return 1;
+}
+
+struct kvm_kernel_irqfd *kvm_arch_irqfd_alloc(void)
+{
+	struct gunyah_irqfd *irqfd;
+
+	irqfd = kzalloc(sizeof(struct gunyah_irqfd), GFP_KERNEL);
+	if (!irqfd)
+		return NULL;
+
+	return &irqfd->irqfd;
+}
+
+void kvm_arch_irqfd_free(struct kvm_kernel_irqfd *kvm_irqfd)
+{
+	struct gunyah_irqfd *irqfd = container_of(kvm_irqfd, struct gunyah_irqfd, irqfd);
+
+	gunyah_vm_remove_resource_ticket(irqfd->ghvm, &irqfd->ticket);
+	kfree(irqfd);
+}
+
+int kvm_arch_irqfd_init(struct kvm_kernel_irqfd *kvm_irqfd)
+{
+	struct gunyah_vm *ghvm = container_of(kvm_irqfd->kvm, struct gunyah_vm, kvm);
+	struct gunyah_irqfd *irqfd = container_of(kvm_irqfd, struct gunyah_irqfd, irqfd);
+
+	kvm_irqfd->set_irq = gunyah_set_irq;
+
+	irqfd->ghvm = ghvm;
+
+	irqfd->ticket.resource_type = GUNYAH_RESOURCE_TYPE_BELL_TX;
+	irqfd->ticket.label = kvm_irqfd->gsi;
+	irqfd->ticket.populate = gunyah_irqfd_populate;
+	irqfd->ticket.unpopulate = gunyah_irqfd_unpopulate;
+
+	return gunyah_vm_add_resource_ticket(ghvm, &irqfd->ticket);
+}
+
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
 {
 	return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
-- 
2.39.5