[PATCH V4 3/9] mshv: Introduce basic mshv bridge device for VFIO to build upon

[Mukesh R <mrathor@linux.microsoft.com>]

Add a new file to implement basic VFIO-MSHV bridge pseudo device. These
functions are called in the VFIO framework, and credits to kvm/vfio.c
as this file was adapted from it. This is a basic version to build upon.

Co-developed-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Mukesh R <mrathor@linux.microsoft.com>
---
 drivers/hv/Makefile       |   3 +-
 drivers/hv/mshv_vfio.c    | 211 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/mshv.h |   1 +
 3 files changed, 214 insertions(+), 1 deletion(-)
 create mode 100644 drivers/hv/mshv_vfio.c

diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
index 888a748cc7cb..9ab6fc254c38 100644
--- a/drivers/hv/Makefile
+++ b/drivers/hv/Makefile
@@ -14,7 +14,8 @@ hv_vmbus-y := vmbus_drv.o \
 hv_vmbus-$(CONFIG_HYPERV_TESTING)	+= hv_debugfs.o
 hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
 mshv_root-y := mshv_root_main.o mshv_synic.o mshv_eventfd.o mshv_irq.o \
-	       mshv_root_hv_call.o mshv_portid_table.o mshv_regions.o
+	       mshv_root_hv_call.o mshv_portid_table.o mshv_regions.o  \
+               mshv_vfio.o
 mshv_root-$(CONFIG_DEBUG_FS) += mshv_debugfs.o
 mshv_root-$(CONFIG_TRACEPOINTS) += mshv_trace.o
 mshv_vtl-y := mshv_vtl_main.o
diff --git a/drivers/hv/mshv_vfio.c b/drivers/hv/mshv_vfio.c
new file mode 100644
index 000000000000..a770b508f080
--- /dev/null
+++ b/drivers/hv/mshv_vfio.c
@@ -0,0 +1,211 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * VFIO-MSHV bridge pseudo device
+ *
+ * Heavily inspired by the VFIO-KVM bridge pseudo device.
+ */
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/vfio.h>
+#include <asm/mshyperv.h>
+
+#include "mshv.h"
+#include "mshv_root.h"
+
+struct mshv_vfio_file {
+	struct list_head node;
+	struct file *file;	/* list of struct mshv_vfio_file */
+};
+
+struct mshv_vfio {
+	struct list_head file_list;
+	struct mutex lock;
+};
+
+static bool mshv_vfio_file_is_valid(struct file *file)
+{
+	bool (*fn)(struct file *file);
+	bool ret;
+
+	fn = symbol_get(vfio_file_is_valid);
+	if (!fn)
+		return false;
+
+	ret = fn(file);
+
+	symbol_put(vfio_file_is_valid);
+
+	return ret;
+}
+
+static long mshv_vfio_file_add(struct mshv_device *mshvdev, unsigned int fd)
+{
+	struct mshv_vfio *mshv_vfio = mshvdev->device_private;
+	struct mshv_vfio_file *mvf;
+	struct file *filp;
+	long ret = 0;
+
+	filp = fget(fd);
+	if (!filp)
+		return -EBADF;
+
+	/* Ensure the FD is a vfio FD. */
+	if (!mshv_vfio_file_is_valid(filp)) {
+		ret = -EINVAL;
+		goto out_fput;
+	}
+
+	mutex_lock(&mshv_vfio->lock);
+
+	list_for_each_entry(mvf, &mshv_vfio->file_list, node) {
+		if (mvf->file == filp) {
+			ret = -EEXIST;
+			goto out_unlock;
+		}
+	}
+
+	mvf = kzalloc(sizeof(*mvf), GFP_KERNEL_ACCOUNT);
+	if (!mvf) {
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+
+	mvf->file = get_file(filp);
+	list_add_tail(&mvf->node, &mshv_vfio->file_list);
+
+out_unlock:
+	mutex_unlock(&mshv_vfio->lock);
+out_fput:
+	fput(filp);
+	return ret;
+}
+
+static long mshv_vfio_file_del(struct mshv_device *mshvdev, unsigned int fd)
+{
+	struct mshv_vfio *mshv_vfio = mshvdev->device_private;
+	struct mshv_vfio_file *mvf;
+	long ret;
+
+	CLASS(fd, f)(fd);
+
+	if (fd_empty(f))
+		return -EBADF;
+
+	ret = -ENOENT;
+	mutex_lock(&mshv_vfio->lock);
+
+	list_for_each_entry(mvf, &mshv_vfio->file_list, node) {
+		if (mvf->file != fd_file(f))
+			continue;
+
+		list_del(&mvf->node);
+		fput(mvf->file);
+		kfree(mvf);
+		ret = 0;
+		break;
+	}
+
+	mutex_unlock(&mshv_vfio->lock);
+	return ret;
+}
+
+static long mshv_vfio_set_file(struct mshv_device *mshvdev, long attr,
+			      void __user *arg)
+{
+	int32_t __user *argp = arg;
+	int32_t fd;
+
+	switch (attr) {
+	case MSHV_DEV_VFIO_FILE_ADD:
+		if (get_user(fd, argp))
+			return -EFAULT;
+		return mshv_vfio_file_add(mshvdev, fd);
+
+	case MSHV_DEV_VFIO_FILE_DEL:
+		if (get_user(fd, argp))
+			return -EFAULT;
+		return mshv_vfio_file_del(mshvdev, fd);
+	}
+
+	return -ENXIO;
+}
+
+static long mshv_vfio_set_attr(struct mshv_device *mshvdev,
+			      struct mshv_device_attr *attr)
+{
+	switch (attr->group) {
+	case MSHV_DEV_VFIO_FILE:
+		return mshv_vfio_set_file(mshvdev, attr->attr,
+					  u64_to_user_ptr(attr->addr));
+	}
+
+	return -ENXIO;
+}
+
+static long mshv_vfio_has_attr(struct mshv_device *mshvdev,
+			      struct mshv_device_attr *attr)
+{
+	switch (attr->group) {
+	case MSHV_DEV_VFIO_FILE:
+		switch (attr->attr) {
+		case MSHV_DEV_VFIO_FILE_ADD:
+		case MSHV_DEV_VFIO_FILE_DEL:
+			return 0;
+		}
+
+		break;
+	}
+
+	return -ENXIO;
+}
+
+static long mshv_vfio_create_device(struct mshv_device *mshvdev)
+{
+	struct mshv_device *tmp;
+	struct mshv_vfio *mshv_vfio;
+
+	/* Only one VFIO "device" per VM */
+	hlist_for_each_entry(tmp, &mshvdev->device_pt->pt_devices,
+			     device_ptnode)
+		if (tmp->device_ops == &mshv_vfio_device_ops)
+			return -EBUSY;
+
+	mshv_vfio = kzalloc_obj(*mshv_vfio);
+	if (mshv_vfio == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&mshv_vfio->file_list);
+	mutex_init(&mshv_vfio->lock);
+
+	mshvdev->device_private = mshv_vfio;
+
+	return 0;
+}
+
+/* This is called from mshv_device_fop_release() */
+static void mshv_vfio_release_device(struct mshv_device *mshvdev)
+{
+	struct mshv_vfio *mv = mshvdev->device_private;
+	struct mshv_vfio_file *mvf, *tmp;
+
+	list_for_each_entry_safe(mvf, tmp, &mv->file_list, node) {
+		fput(mvf->file);
+		list_del(&mvf->node);
+		kfree(mvf);
+	}
+
+	kfree(mv);
+	kfree(mshvdev);
+}
+
+struct mshv_device_ops mshv_vfio_device_ops = {
+	.device_name = "mshv-vfio",
+	.device_create = mshv_vfio_create_device,
+	.device_release = mshv_vfio_release_device,
+	.device_set_attr = mshv_vfio_set_attr,
+	.device_has_attr = mshv_vfio_has_attr,
+};
diff --git a/include/uapi/linux/mshv.h b/include/uapi/linux/mshv.h
index be6fe3ee8707..b038a79786d2 100644
--- a/include/uapi/linux/mshv.h
+++ b/include/uapi/linux/mshv.h
@@ -254,6 +254,7 @@ struct mshv_root_hvcall {
 #define MSHV_GET_GPAP_ACCESS_BITMAP	_IOWR(MSHV_IOCTL, 0x06, struct mshv_gpap_access_bitmap)
 /* Generic hypercall */
 #define MSHV_ROOT_HVCALL		_IOWR(MSHV_IOCTL, 0x07, struct mshv_root_hvcall)
+#define MSHV_CREATE_DEVICE             _IOWR(MSHV_IOCTL, 0x08, struct mshv_create_device)
 
 /*
  ********************************
-- 
2.51.2.vfs.0.1