[RFC 01/20] iommu/iommufd: Add /dev/iommu core

[Liu Yi L <yi.l.liu@intel.com>]

/dev/iommu aims to provide a unified interface for managing I/O address
spaces for devices assigned to userspace. This patch adds the initial
framework to create a /dev/iommu node. Each open of this node returns an
iommufd. And this fd is the handle for userspace to initiate its I/O
address space management.

One open:
- We call this feature as IOMMUFD in Kconfig in this RFC. However this
  name is not clear enough to indicate its purpose to user. Back to 2010
  vfio even introduced a /dev/uiommu [1] as the predecessor of its
  container concept. Is that a better name? Appreciate opinions here.

[1] https://lore.kernel.org/kvm/4c0eb470.1HMjondO00NIvFM6%25pugs@cisco.com/

Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
---
 drivers/iommu/Kconfig           |   1 +
 drivers/iommu/Makefile          |   1 +
 drivers/iommu/iommufd/Kconfig   |  11 ++++
 drivers/iommu/iommufd/Makefile  |   2 +
 drivers/iommu/iommufd/iommufd.c | 112 ++++++++++++++++++++++++++++++++
 5 files changed, 127 insertions(+)
 create mode 100644 drivers/iommu/iommufd/Kconfig
 create mode 100644 drivers/iommu/iommufd/Makefile
 create mode 100644 drivers/iommu/iommufd/iommufd.c

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 07b7c25cbed8..a83ce0acd09d 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -136,6 +136,7 @@ config MSM_IOMMU
 
 source "drivers/iommu/amd/Kconfig"
 source "drivers/iommu/intel/Kconfig"
+source "drivers/iommu/iommufd/Kconfig"
 
 config IRQ_REMAP
 	bool "Support for Interrupt Remapping"
diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
index c0fb0ba88143..719c799f23ad 100644
--- a/drivers/iommu/Makefile
+++ b/drivers/iommu/Makefile
@@ -29,3 +29,4 @@ obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu.o
 obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
 obj-$(CONFIG_IOMMU_SVA_LIB) += iommu-sva-lib.o io-pgfault.o
 obj-$(CONFIG_SPRD_IOMMU) += sprd-iommu.o
+obj-$(CONFIG_IOMMUFD) += iommufd/
diff --git a/drivers/iommu/iommufd/Kconfig b/drivers/iommu/iommufd/Kconfig
new file mode 100644
index 000000000000..9fb7769a815d
--- /dev/null
+++ b/drivers/iommu/iommufd/Kconfig
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config IOMMUFD
+	tristate "I/O Address Space management framework for passthrough devices"
+	select IOMMU_API
+	default n
+	help
+	  provides unified I/O address space management framework for
+	  isolating untrusted DMAs via devices which are passed through
+	  to userspace drivers.
+
+	  If you don't know what to do here, say N.
diff --git a/drivers/iommu/iommufd/Makefile b/drivers/iommu/iommufd/Makefile
new file mode 100644
index 000000000000..54381a01d003
--- /dev/null
+++ b/drivers/iommu/iommufd/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_IOMMUFD) += iommufd.o
diff --git a/drivers/iommu/iommufd/iommufd.c b/drivers/iommu/iommufd/iommufd.c
new file mode 100644
index 000000000000..710b7e62988b
--- /dev/null
+++ b/drivers/iommu/iommufd/iommufd.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * I/O Address Space Management for passthrough devices
+ *
+ * Copyright (C) 2021 Intel Corporation
+ *
+ * Author: Liu Yi L <yi.l.liu@intel.com>
+ */
+
+#define pr_fmt(fmt)    "iommufd: " fmt
+
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/miscdevice.h>
+#include <linux/mutex.h>
+#include <linux/iommu.h>
+
+/* Per iommufd */
+struct iommufd_ctx {
+	refcount_t refs;
+};
+
+static int iommufd_fops_open(struct inode *inode, struct file *filep)
+{
+	struct iommufd_ctx *ictx;
+	int ret = 0;
+
+	ictx = kzalloc(sizeof(*ictx), GFP_KERNEL);
+	if (!ictx)
+		return -ENOMEM;
+
+	refcount_set(&ictx->refs, 1);
+	filep->private_data = ictx;
+
+	return ret;
+}
+
+static void iommufd_ctx_put(struct iommufd_ctx *ictx)
+{
+	if (refcount_dec_and_test(&ictx->refs))
+		kfree(ictx);
+}
+
+static int iommufd_fops_release(struct inode *inode, struct file *filep)
+{
+	struct iommufd_ctx *ictx = filep->private_data;
+
+	filep->private_data = NULL;
+
+	iommufd_ctx_put(ictx);
+
+	return 0;
+}
+
+static long iommufd_fops_unl_ioctl(struct file *filep,
+				   unsigned int cmd, unsigned long arg)
+{
+	struct iommufd_ctx *ictx = filep->private_data;
+	long ret = -EINVAL;
+
+	if (!ictx)
+		return ret;
+
+	switch (cmd) {
+	default:
+		pr_err_ratelimited("unsupported cmd %u\n", cmd);
+		break;
+	}
+	return ret;
+}
+
+static const struct file_operations iommufd_fops = {
+	.owner		= THIS_MODULE,
+	.open		= iommufd_fops_open,
+	.release	= iommufd_fops_release,
+	.unlocked_ioctl	= iommufd_fops_unl_ioctl,
+};
+
+static struct miscdevice iommu_misc_dev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "iommu",
+	.fops = &iommufd_fops,
+	.nodename = "iommu",
+	.mode = 0666,
+};
+
+static int __init iommufd_init(void)
+{
+	int ret;
+
+	ret = misc_register(&iommu_misc_dev);
+	if (ret) {
+		pr_err("failed to register misc device\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static void __exit iommufd_exit(void)
+{
+	misc_deregister(&iommu_misc_dev);
+}
+
+module_init(iommufd_init);
+module_exit(iommufd_exit);
+
+MODULE_AUTHOR("Liu Yi L <yi.l.liu@intel.com>");
+MODULE_DESCRIPTION("I/O Address Space Management for passthrough devices");
+MODULE_LICENSE("GPL v2");
-- 
2.25.1