Enable support for creating irqfds which can raise an interrupt on a
Gunyah virtual machine. irqfds are exposed to userspace as a Gunyah VM
function with the name "irqfd". If the VM devicetree is not configured
to create a doorbell with the corresponding label, userspace will still
be able to assert the eventfd but no interrupt will be raised on the
guest.

Co-developed-by: Prakruthi Deepak Heragu <redacted>
Signed-off-by: Prakruthi Deepak Heragu <redacted>
Signed-off-by: Elliot Berman <redacted>
---
  Documentation/virt/gunyah/vm-manager.rst |  22 +++
  drivers/virt/gunyah/Kconfig              |   9 ++
  drivers/virt/gunyah/Makefile             |   1 +
  drivers/virt/gunyah/gunyah_irqfd.c       | 166 +++++++++++++++++++++++
  include/linux/gunyah.h                   |   5 +
  include/uapi/linux/gunyah.h              |  11 +-
  6 files changed, 213 insertions(+), 1 deletion(-)
  create mode 100644 drivers/virt/gunyah/gunyah_irqfd.c

diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
index d11267d59802..b6cf8db826b8 100644
--- a/Documentation/virt/gunyah/vm-manager.rst
+++ b/Documentation/virt/gunyah/vm-manager.rst

@@ -142,3 +142,25 @@ The vcpu type will register with the VM Manager to expect to control
  vCPU number `vcpu_id`. It returns a file descriptor allowing interaction with
  the vCPU. See the Gunyah vCPU API description sections for interacting with
  the Gunyah vCPU file descriptors.
+
+Type: "irqfd"
+^^^^^^^^^^^^^
+
+::
+
+  struct gh_fn_irqfd_arg {
+	__u32 fd;
+	__u32 label;
+  #define GH_IRQFD_LEVEL			(1UL << 0)
+  #define GH_IRQFD_DEASSIGN		(1UL << 1)
+	__u32 flags;
+  };
+
+Allows setting an eventfd to directly trigger a guest interrupt.
+irqfd.fd specifies the file descriptor to use as the eventfd.
+irqfd.label corresponds to the doorbell label used in the guest VM's devicetree.
+The irqfd is removed using the GH_IRQFD_DEASSIGN flag and specifying at least
+the irqfd.label.
+
+GH_IRQFD_LEVEL configures the corresponding doorbell to behave like a level
+triggered interrupt.

diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
index 4c1c6110b50e..2cde24d429d1 100644
--- a/drivers/virt/gunyah/Kconfig
+++ b/drivers/virt/gunyah/Kconfig

@@ -26,3 +26,12 @@ config GUNYAH_VCPU
  	  VMMs can also handle stage 2 faults of the vCPUs.
  
  	  Say Y/M here if unsure and you want to support Gunyah VMMs.
+
+config GUNYAH_IRQFD
+	tristate "Gunyah irqfd interface"
+	depends on GUNYAH
+	help
+	  Enable kernel support for creating irqfds which can raise an interrupt
+	  on Gunyah virtual machine.
+
+	  Say Y/M here if unsure and you want to support Gunyah VMMs.

diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
index 2d1b604a7b03..6cf756bfa3c2 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile

@@ -7,3 +7,4 @@ gunyah_rsc_mgr-y += rsc_mgr.o rsc_mgr_rpc.o vm_mgr.o vm_mgr_mm.o
  obj-$(CONFIG_GUNYAH) += gunyah_rsc_mgr.o
  
  obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
+obj-$(CONFIG_GUNYAH_IRQFD) += gunyah_irqfd.o

diff --git a/drivers/virt/gunyah/gunyah_irqfd.c b/drivers/virt/gunyah/gunyah_irqfd.c
new file mode 100644
index 000000000000..a3be9ca2377a
--- /dev/null
+++ b/drivers/virt/gunyah/gunyah_irqfd.c

@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/eventfd.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/gunyah.h>
+#include <linux/gunyah_vm_mgr.h>
+#include <linux/kref.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/printk.h>
+
+#include <uapi/linux/gunyah.h>
+
+struct gunyah_irqfd {
+	struct gunyah_resource *ghrsc;
+	struct gunyah_vm_resource_ticket ticket;
+	struct gunyah_vm_function *f;
+
+	struct kref kref;
+	bool level;
+
+	struct eventfd_ctx *ctx;
+	wait_queue_entry_t wait;
+	poll_table pt;
+	struct fd fd;
+};
+
+static void gh_irqfd_cleanup(struct kref *kref)
+{
+	struct gunyah_irqfd *irqfd = container_of(kref, struct gunyah_irqfd, kref);
+
+	kfree(irqfd);
+}
+
+static int irqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode, int sync, void *key)
+{
+	struct gunyah_irqfd *irqfd = container_of(wait, struct gunyah_irqfd, wait);
+	__poll_t flags = key_to_poll(key);
+	u64 enable_mask = GH_DBL_NONBLOCK;
+	u64 old_flags;
+	int ret = 0;
+
+	if (flags & EPOLLIN) {
+		if (irqfd->ghrsc) {
+			ret = gh_hypercall_dbl_send(irqfd->ghrsc->capid, enable_mask, &old_flags);
+			if (ret)
+				pr_err("Failed to assert irq %d\n", irqfd->f->fn.irqfd.label);
+		}
+	}
+
+	return 0;
+}
+
+static void irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh, poll_table *pt)
+{
+	struct gunyah_irqfd *irq_ctx = container_of(pt, struct gunyah_irqfd, pt);
+
+	add_wait_queue(wqh, &irq_ctx->wait);
+}
+
+static int gunyah_irqfd_populate(struct gunyah_vm_resource_ticket *ticket,
+				struct gunyah_resource *ghrsc)
+{
+	struct gunyah_irqfd *irqfd = container_of(ticket, struct gunyah_irqfd, ticket);
+	u64 enable_mask = GH_DBL_NONBLOCK;
+	u64 ack_mask = ~0;
+	int ret = 0;
+
+	irqfd->ghrsc = ghrsc;
+	if (irqfd->level) {
+		ret = gh_hypercall_dbl_set_mask(irqfd->ghrsc->capid, enable_mask, ack_mask);
+		if (ret)
+			pr_warn("irq %d couldn't be set as level triggered. Might cause IRQ storm if asserted\n",
+				irqfd->f->fn.irqfd.label);
+	}
+	kref_get(&irqfd->kref);
+
+	return 0;
+}
+
+static void gunyah_irqfd_unpopulate(struct gunyah_vm_resource_ticket *ticket,
+					struct gunyah_resource *ghrsc)
+{
+	struct gunyah_irqfd *irqfd = container_of(ticket, struct gunyah_irqfd, ticket);
+	u64 cnt;
+
+	eventfd_ctx_remove_wait_queue(irqfd->ctx, &irqfd->wait, &cnt);
+	eventfd_ctx_put(irqfd->ctx);

+	eventfd_ctx_put(irqfd->ctx);
+err_fdput:
+	fdput(irqfd->fd);
+err_free:
+	kfree(irqfd);
+	return r;
+}
+
+static void gunyah_irqfd_release(struct gunyah_vm_function *f)
+{
+	struct gunyah_irqfd *irqfd = f->data;
+
+	/* unpopulate will trigger clean up of the eventfd */
+	ghvm_remove_resource_ticket(irqfd->f->ghvm, &irqfd->ticket);
+}
+
+DECLARE_GUNYAH_VM_FUNCTION_INIT(irqfd, gunyah_irqfd_bind, gunyah_irqfd_release);
+MODULE_DESCRIPTION("Gunyah irqfds");
+MODULE_LICENSE("GPL");

diff --git a/include/linux/gunyah.h b/include/linux/gunyah.h
index ac4879940c10..6b363707a901 100644
--- a/include/linux/gunyah.h
+++ b/include/linux/gunyah.h

@@ -33,6 +33,11 @@ struct gunyah_resource {
  	u32 rm_label;
  };
  
+/**
+ * Gunyah Doorbells
+ */
+#define GH_DBL_NONBLOCK		BIT(32)
+
  /**
   * Gunyah Message Queues
   */

diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index b4afb11f538a..a947f0317ca9 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h

@@ -57,10 +57,19 @@ struct gh_fn_vcpu_arg {
  	__u32 vcpu_id;
  };
  
+struct gh_fn_irqfd_arg {
+	__u32 fd;
+	__u32 label;
+#define GH_IRQFD_LEVEL			(1UL << 0)
+#define GH_IRQFD_DEASSIGN		(1UL << 1)
+	__u32 flags;