[PATCH v13 23/24] 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 |   2 +-
 drivers/virt/gunyah/Kconfig              |   9 ++
 drivers/virt/gunyah/Makefile             |   1 +
 drivers/virt/gunyah/gunyah_ioeventfd.c   | 130 +++++++++++++++++++++++
 include/uapi/linux/gunyah.h              |  37 +++++++
 5 files changed, 178 insertions(+), 1 deletion(-)
 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 c4960948c779..87838c5b5945 100644
--- a/Documentation/virt/gunyah/vm-manager.rst
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -115,7 +115,7 @@ the VM *before* the VM starts.
 The argument types are documented below:
 
 .. kernel-doc:: include/uapi/linux/gunyah.h
-   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags
+   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags gh_fn_ioeventfd_arg gh_ioeventfd_flags
 
 Gunyah VCPU API Descriptions
 ----------------------------
diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
index bc2c46d9df94..63bebc5b9f82 100644
--- a/drivers/virt/gunyah/Kconfig
+++ b/drivers/virt/gunyah/Kconfig
@@ -48,3 +48,12 @@ 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 ad212a1cf967..63ca11e74796 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile
@@ -8,3 +8,4 @@ obj-$(CONFIG_GUNYAH) += gunyah.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..5b1b9fd9ac3a
--- /dev/null
+++ b/drivers/virt/gunyah/gunyah_ioeventfd.c
@@ -0,0 +1,130 @@
+// 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 gh_ioeventfd {
+	struct gh_vm_function_instance *f;
+	struct gh_vm_io_handler io_handler;
+
+	struct eventfd_ctx *ctx;
+};
+
+static int gh_write_ioeventfd(struct gh_vm_io_handler *io_dev, u64 addr, u32 len, u64 data)
+{
+	struct gh_ioeventfd *iofd = container_of(io_dev, struct gh_ioeventfd, io_handler);
+
+	eventfd_signal(iofd->ctx, 1);
+	return 0;
+}
+
+static struct gh_vm_io_handler_ops io_ops = {
+	.write = gh_write_ioeventfd,
+};
+
+static long gh_ioeventfd_bind(struct gh_vm_function_instance *f)
+{
+	const struct gh_fn_ioeventfd_arg *args = f->argp;
+	struct gh_ioeventfd *iofd;
+	struct eventfd_ctx *ctx;
+	int ret;
+
+	if (f->arg_size != sizeof(*args))
+		return -EINVAL;
+
+	/* All other flag bits are reserved for future use */
+	if (args->flags & ~GH_IOEVENTFD_FLAGS_DATAMATCH)
+		return -EINVAL;
+
+	/* 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 (overflows_type(args->addr + args->len, u64))
+		return -EINVAL;
+
+	/* ioeventfd with no length can't be combined with DATAMATCH */
+	if (!args->len && (args->flags & GH_IOEVENTFD_FLAGS_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_FLAGS_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_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 gh_ioevent_unbind(struct gh_vm_function_instance *f)
+{
+	struct gh_ioeventfd *iofd = f->data;
+
+	eventfd_ctx_put(iofd->ctx);
+	gh_vm_remove_io_handler(iofd->f->ghvm, &iofd->io_handler);
+	kfree(iofd);
+}
+
+static bool gh_ioevent_compare(const struct gh_vm_function_instance *f,
+				const void *arg, size_t size)
+{
+	const struct gh_fn_ioeventfd_arg *instance = f->argp,
+					 *other = arg;
+
+	if (sizeof(*other) != size)
+		return false;
+
+	return instance->addr == other->addr;
+}
+
+DECLARE_GH_VM_FUNCTION_INIT(ioeventfd, GH_FN_IOEVENTFD, 3,
+				gh_ioeventfd_bind, gh_ioevent_unbind,
+				gh_ioevent_compare);
+MODULE_DESCRIPTION("Gunyah ioeventfd VM Function");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index 0c480c622686..fa1cae7419d2 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h
@@ -79,10 +79,13 @@ struct gh_vm_dtb_config {
  *              Return: file descriptor to manipulate the vcpu.
  * @GH_FN_IRQFD: register eventfd to assert a Gunyah doorbell
  *               &struct gh_fn_desc.arg is a pointer to &struct gh_fn_irqfd_arg
+ * @GH_FN_IOEVENTFD: register ioeventfd to trigger when VM faults on parameter
+ *                   &struct gh_fn_desc.arg is a pointer to &struct gh_fn_ioeventfd_arg
  */
 enum gh_fn_type {
 	GH_FN_VCPU = 1,
 	GH_FN_IRQFD,
+	GH_FN_IOEVENTFD,
 };
 
 #define GH_FN_MAX_ARG_SIZE		256
@@ -134,6 +137,40 @@ struct gh_fn_irqfd_arg {
 	__u32 padding;
 };
 
+/**
+ * enum gh_ioeventfd_flags - flags for use in gh_fn_ioeventfd_arg
+ * @GH_IOEVENTFD_FLAGS_DATAMATCH: the event will be signaled only if the
+ *                                written value to the registered address is
+ *                                equal to &struct gh_fn_ioeventfd_arg.datamatch
+ */
+enum gh_ioeventfd_flags {
+	GH_IOEVENTFD_FLAGS_DATAMATCH	= 1UL << 0,
+};
+
+/**
+ * struct gh_fn_ioeventfd_arg - Arguments to create an ioeventfd function
+ * @datamatch: data used when GH_IOEVENTFD_DATAMATCH is set
+ * @addr: Address in guest memory
+ * @len: Length of access
+ * @fd: When ioeventfd is matched, this eventfd is written
+ * @flags: See &enum gh_ioeventfd_flags
+ * @padding: padding bytes
+ *
+ * Create this function with &GH_VM_ADD_FUNCTION using type &GH_FN_IOEVENTFD.
+ *
+ * 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.
+ */
+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;
+	__u32 flags;
+	__u32 padding;
+};
+
 /**
  * struct gh_fn_desc - Arguments to create a VM function
  * @type: Type of the function. See &enum gh_fn_type.
-- 
2.40.0