[PATCH v9 27/27] virt: gunyah: Add ioeventfd

[Elliot Berman <quic_eberman@quicinc.com>]

Allow userspace to attach an ioeventfd to an mmio address within the guest.

Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
 Documentation/virt/gunyah/vm-manager.rst |  21 +++++
 drivers/virt/gunyah/Kconfig              |   9 ++
 drivers/virt/gunyah/Makefile             |   1 +
 drivers/virt/gunyah/gunyah_ioeventfd.c   | 109 +++++++++++++++++++++++
 include/uapi/linux/gunyah.h              |  10 +++
 5 files changed, 150 insertions(+)
 create mode 100644 drivers/virt/gunyah/gunyah_ioeventfd.c

diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
index b6cf8db826b8..19ec859a7912 100644
--- a/Documentation/virt/gunyah/vm-manager.rst
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -164,3 +164,24 @@ the irqfd.label.
 
 GH_IRQFD_LEVEL configures the corresponding doorbell to behave like a level
 triggered interrupt.
+
+Type: "ioeventfd"
+^^^^^^^^^^^^^^^^^
+
+::
+
+  struct gh_fn_ioeventfd_arg {
+	__u64 datamatch;
+	__u64 addr;        /* legal mmio address */
+	__u32 len;         /* 1, 2, 4, or 8 bytes */
+	__s32 fd;
+  #define GH_IOEVENTFD_DATAMATCH		(1UL << 0)
+	__u32 flags;
+  };
+
+Attaches an ioeventfd to a legal mmio address within the guest. A guest write
+in the registered address will signal the provided event instead of triggering
+an exit on the GH_VCPU_RUN ioctl.
+
+If datamatch flag is set, the event will be signaled only if the written value
+to the registered address is equal to datamatch in struct gh_fn_ioeventfd_arg.
diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
index 2cde24d429d1..bd8e31184962 100644
--- a/drivers/virt/gunyah/Kconfig
+++ b/drivers/virt/gunyah/Kconfig
@@ -35,3 +35,12 @@ config GUNYAH_IRQFD
 	  on Gunyah virtual machine.
 
 	  Say Y/M here if unsure and you want to support Gunyah VMMs.
+
+config GUNYAH_IOEVENTFD
+	tristate "Gunyah ioeventfd interface"
+	depends on GUNYAH
+	help
+	  Enable kernel support for creating ioeventfds which can alert userspace
+	  when a Gunyah virtual machine accesses a memory address.
+
+	  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 6cf756bfa3c2..7347b1470491 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile
@@ -8,3 +8,4 @@ obj-$(CONFIG_GUNYAH) += gunyah_rsc_mgr.o
 
 obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
 obj-$(CONFIG_GUNYAH_IRQFD) += gunyah_irqfd.o
+obj-$(CONFIG_GUNYAH_IOEVENTFD) += gunyah_ioeventfd.o
diff --git a/drivers/virt/gunyah/gunyah_ioeventfd.c b/drivers/virt/gunyah/gunyah_ioeventfd.c
new file mode 100644
index 000000000000..c16a6725fe7e
--- /dev/null
+++ b/drivers/virt/gunyah/gunyah_ioeventfd.c
@@ -0,0 +1,109 @@
+// 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/module.h>
+#include <linux/printk.h>
+
+#include <uapi/linux/gunyah.h>
+
+struct gunyah_ioeventfd {
+	struct gunyah_vm_function *f;
+	struct gunyah_vm_io_handler io_handler;
+
+	struct eventfd_ctx *ctx;
+};
+
+static int gh_write_ioeventfd(struct gunyah_vm_io_handler *io_dev, u64 addr, u32 len, u64 data)
+{
+	struct gunyah_ioeventfd *iofd = container_of(io_dev, struct gunyah_ioeventfd, io_handler);
+
+	eventfd_signal(iofd->ctx, 1);
+	return 0;
+}
+
+static struct gunyah_vm_io_handler_ops io_ops = {
+	.write = gh_write_ioeventfd,
+};
+
+static long gunyah_ioeventfd_bind(struct gunyah_vm_function *f)
+{
+	struct eventfd_ctx *ctx = NULL;
+	struct gunyah_ioeventfd *iofd;
+	const struct gh_fn_ioeventfd_arg *args = &f->fn.ioeventfd;
+	int ret;
+
+	/* must be natural-word sized, or 0 to ignore length */
+	switch (args->len) {
+	case 0:
+	case 1:
+	case 2:
+	case 4:
+	case 8:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* check for range overflow */
+	if (args->addr + args->len < args->addr)
+		return -EINVAL;
+
+	/* ioeventfd with no length can't be combined with DATAMATCH */
+	if (!args->len && (args->flags & GH_IOEVENTFD_DATAMATCH))
+		return -EINVAL;
+
+	ctx = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	iofd = kzalloc(sizeof(*iofd), GFP_KERNEL);
+	if (!iofd) {
+		ret = -ENOMEM;
+		goto err_eventfd;
+	}
+
+	f->data = iofd;
+	iofd->f = f;
+
+	iofd->ctx = ctx;
+
+	if (args->flags & GH_IOEVENTFD_DATAMATCH) {
+		iofd->io_handler.datamatch = true;
+		iofd->io_handler.len = args->len;
+		iofd->io_handler.data = args->datamatch;
+	}
+	iofd->io_handler.addr = args->addr;
+	iofd->io_handler.ops = &io_ops;
+
+	ret = gh_vm_mgr_add_io_handler(f->ghvm, &iofd->io_handler);
+	if (ret)
+		goto err_io_dev_add;
+
+	return 0;
+
+err_io_dev_add:
+	kfree(iofd);
+err_eventfd:
+	eventfd_ctx_put(ctx);
+	return ret;
+}
+
+static void gunyah_ioeventfd_release(struct gunyah_vm_function *f)
+{
+	struct gunyah_ioeventfd *iofd = f->data;
+
+	eventfd_ctx_put(iofd->ctx);
+	gh_vm_mgr_remove_io_handler(iofd->f->ghvm, &iofd->io_handler);
+	kfree(iofd);
+}
+
+DECLARE_GUNYAH_VM_FUNCTION_INIT(ioeventfd, gunyah_ioeventfd_bind, gunyah_ioeventfd_release);
+MODULE_DESCRIPTION("Gunyah ioeventfds");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index a947f0317ca9..3cc387f0831a 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h
@@ -65,11 +65,21 @@ struct gh_fn_irqfd_arg {
 	__u32 flags;
 };
 
+struct gh_fn_ioeventfd_arg {
+	__u64 datamatch;
+	__u64 addr;        /* legal mmio address */
+	__u32 len;         /* 1, 2, 4, or 8 bytes; or 0 to ignore length */
+	__s32 fd;
+#define GH_IOEVENTFD_DATAMATCH		(1UL << 0)
+	__u32 flags;
+};
+
 struct gh_vm_function {
 	char name[GUNYAH_FUNCTION_NAME_SIZE];
 	union {
 		struct gh_fn_vcpu_arg vcpu;
 		struct gh_fn_irqfd_arg irqfd;
+		struct gh_fn_ioeventfd_arg ioeventfd;
 		char data[GUNYAH_FUNCTION_MAX_ARG_SIZE];
 	};
 };
-- 
2.39.0