FROMLIST: virt: gunyah: Add ioeventfd

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

Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Change-Id: I9565c47de3cba3e76528e36088d773b3ce31178e
Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Bug: 268234781
Link: https://lore.kernel.org/all/20230304010632.2127470-26-quic_eberman@quicinc.com/

Documentation/virt/gunyah/vm-manager.rst

@@ -124,7 +124,7 @@ the VM starts.
 The possible types are documented below:
 
 .. kernel-doc:: include/uapi/linux/gunyah.h
-   :identifiers: GH_FN_VCPU gh_fn_vcpu_arg GH_FN_IRQFD gh_fn_irqfd_arg
+   :identifiers: GH_FN_VCPU gh_fn_vcpu_arg GH_FN_IRQFD gh_fn_irqfd_arg GH_FN_IOEVENTFD gh_fn_ioeventfd_arg
 
 Gunyah VCPU API Descriptions
 ----------------------------

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.

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

drivers/virt/gunyah/gunyah_ioeventfd.c

@@ -0,0 +1,117 @@
+// 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 eventfd_ctx *ctx = NULL;
+	struct gh_ioeventfd *iofd;
+	int ret;
+
+	if (f->arg_size != sizeof(*args))
+		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 (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;
+
+	/* All other flag bits are reserved for future use */
+	if (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_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);
+}
+
+DECLARE_GH_VM_FUNCTION_INIT(ioeventfd, GH_FN_IOEVENTFD,
+				gh_ioeventfd_bind, gh_ioevent_unbind);
+MODULE_DESCRIPTION("Gunyah ioeventfds");
+MODULE_LICENSE("GPL");

include/uapi/linux/gunyah.h

@@ -89,6 +89,23 @@ struct gh_vm_dtb_config {
  */
 #define GH_FN_IRQFD 		2
 
+/**
+ * GH_FN_IOEVENTFD - register ioeventfd to trigger when VM faults on parameter
+ *
+ * gh_fn_desc is filled with gh_fn_ioeventfd_arg
+ *
+ * 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 GH_IOEVENTFD_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.
+ *
+ * Return: 0
+ */
+#define GH_FN_IOEVENTFD 	3
+
 #define GH_FN_MAX_ARG_SIZE		256
 
 /**
@@ -118,6 +135,26 @@ struct gh_fn_irqfd_arg {
 
 #define GH_IOEVENTFD_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: If GH_IOEVENTFD_DATAMATCH flag is set, the event will be signaled
+ *         only if the written value to the registered address is equal to
+ *         @datamatch
+ * @padding: padding bytes
+ */
+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 GH_FN_* macro for supported types