iommufd: File descriptor, context, kconfig and makefiles

This is the basic infrastructure of a new miscdevice to hold the iommufd
IOCTL API.

It provides:
 - A miscdevice to create file descriptors to run the IOCTL interface over

 - A table based ioctl dispatch and centralized extendable pre-validation
   step

 - An xarray mapping userspace ID's to kernel objects. The design has
   multiple inter-related objects held within in a single IOMMUFD fd

 - A simple usage count to build a graph of object relations and protect
   against hostile userspace racing ioctls

The only IOCTL provided in this patch is the generic 'destroy any object
by handle' operation.

Link: https://lore.kernel.org/r/6-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
new file mode 100644
index 000000000000..d1817472c273
--- /dev/null
+++ b/include/linux/iommufd.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Intel Corporation
+ * Copyright (c) 2021-2022, NVIDIA CORPORATION & AFFILIATES
+ */
+#ifndef __LINUX_IOMMUFD_H
+#define __LINUX_IOMMUFD_H
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+
+struct iommufd_ctx;
+struct file;
+
+void iommufd_ctx_get(struct iommufd_ctx *ictx);
+
+#if IS_ENABLED(CONFIG_IOMMUFD)
+struct iommufd_ctx *iommufd_ctx_from_file(struct file *file);
+void iommufd_ctx_put(struct iommufd_ctx *ictx);
+#else /* !CONFIG_IOMMUFD */
+static inline struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void iommufd_ctx_put(struct iommufd_ctx *ictx)
+{
+}
+#endif /* CONFIG_IOMMUFD */
+#endif