// SPDX-License-Identifier: GPL-2.0-only
/*
 * VDPA simulator for block device.
 *
 * Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved.
 * Copyright (c) 2021, Red Hat Inc. All rights reserved.
 *
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/vringh.h>
#include <linux/vdpa.h>
#include <uapi/linux/virtio_blk.h>

#include "vdpa_sim.h"

#define DRV_VERSION  "0.1"
#define DRV_AUTHOR   "Max Gurtovoy <mgurtovoy@nvidia.com>"
#define DRV_DESC     "vDPA Device Simulator for block device"
#define DRV_LICENSE  "GPL v2"

#define VDPASIM_BLK_FEATURES	(VDPASIM_FEATURES | \
				 (1ULL << VIRTIO_BLK_F_FLUSH)    | \
				 (1ULL << VIRTIO_BLK_F_SIZE_MAX) | \
				 (1ULL << VIRTIO_BLK_F_SEG_MAX)  | \
				 (1ULL << VIRTIO_BLK_F_BLK_SIZE) | \
				 (1ULL << VIRTIO_BLK_F_TOPOLOGY) | \
				 (1ULL << VIRTIO_BLK_F_MQ)       | \
				 (1ULL << VIRTIO_BLK_F_DISCARD)  | \
				 (1ULL << VIRTIO_BLK_F_WRITE_ZEROES))

#define VDPASIM_BLK_CAPACITY	0x40000
#define VDPASIM_BLK_SIZE_MAX	0x1000
#define VDPASIM_BLK_SEG_MAX	32
#define VDPASIM_BLK_DWZ_MAX_SECTORS UINT_MAX

/* 1 virtqueue, 1 address space, 1 virtqueue group */
#define VDPASIM_BLK_VQ_NUM	1
#define VDPASIM_BLK_AS_NUM	1
#define VDPASIM_BLK_GROUP_NUM	1

struct vdpasim_blk {
	struct vdpasim vdpasim;
	void *buffer;
	bool shared_backend;
};

static struct vdpasim_blk *sim_to_blk(struct vdpasim *vdpasim)
{
	return container_of(vdpasim, struct vdpasim_blk, vdpasim);
}

static char vdpasim_blk_id[VIRTIO_BLK_ID_BYTES] = "vdpa_blk_sim";

static bool shared_backend;
module_param(shared_backend, bool, 0444);
MODULE_PARM_DESC(shared_backend, "Enable the shared backend between virtio-blk devices");

static void *shared_buffer;
/* mutex to synchronize shared_buffer access */
static DEFINE_MUTEX(shared_buffer_mutex);

static void vdpasim_blk_buffer_lock(struct vdpasim_blk *blk)
{
	if (blk->shared_backend)
		mutex_lock(&shared_buffer_mutex);
}

static void vdpasim_blk_buffer_unlock(struct vdpasim_blk *blk)
{
	if (blk->shared_backend)
		mutex_unlock(&shared_buffer_mutex);
}

static bool vdpasim_blk_check_range(struct vdpasim *vdpasim, u64 start_sector,
				    u64 num_sectors, u64 max_sectors)
{
	if (start_sector > VDPASIM_BLK_CAPACITY) {
		dev_dbg(&vdpasim->vdpa.dev,
			"starting sector exceeds the capacity - start: 0x%llx capacity: 0x%x\n",
			start_sector, VDPASIM_BLK_CAPACITY);
	}

	if (num_sectors > max_sectors) {
		dev_dbg(&vdpasim->vdpa.dev,
			"number of sectors exceeds the max allowed in a request - num: 0x%llx max: 0x%llx\n",
			num_sectors, max_sectors);
		return false;
	}

	if (num_sectors > VDPASIM_BLK_CAPACITY - start_sector) {
		dev_dbg(&vdpasim->vdpa.dev,
			"request exceeds the capacity - start: 0x%llx num: 0x%llx capacity: 0x%x\n",
			start_sector, num_sectors, VDPASIM_BLK_CAPACITY);
		return false;
	}

	return true;
}

/* Returns 'true' if the request is handled (with or without an I/O error)
 * and the status is correctly written in the last byte of the 'in iov',
 * 'false' otherwise.
 */
static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
				   struct vdpasim_virtqueue *vq)
{
	struct vdpasim_blk *blk = sim_to_blk(vdpasim);
	size_t pushed = 0, to_pull, to_push;
	struct virtio_blk_outhdr hdr;
	bool handled = false;
	ssize_t bytes;
	loff_t offset;
	u64 sector;
	u8 status;
	u32 type;
	int ret;

	ret = vringh_getdesc_iotlb(&vq->vring, &vq->out_iov, &vq->in_iov,
				   &vq->head, GFP_ATOMIC);
	if (ret != 1)
		return false;

	if (vq->out_iov.used < 1 || vq->in_iov.used < 1) {
		dev_dbg(&vdpasim->vdpa.dev, "missing headers - out_iov: %u in_iov %u\n",
			vq->out_iov.used, vq->in_iov.used);
		goto err;
	}

	if (vq->in_iov.iov[vq->in_iov.used - 1].iov_len < 1) {
		dev_dbg(&vdpasim->vdpa.dev, "request in header too short\n");
		goto err;
	}

	/* The last byte is the status and we checked if the last iov has
	 * enough room for it.
	 */
	to_push = vringh_kiov_length(&vq->in_iov) - 1;

	to_pull = vringh_kiov_length(&vq->out_iov);

	bytes = vringh_iov_pull_iotlb(&vq->vring, &vq->out_iov, &hdr,
				      sizeof(hdr));
	if (bytes != sizeof(hdr)) {
		dev_dbg(&vdpasim->vdpa.dev, "request out header too short\n");
		goto err;
	}

	to_pull -= bytes;

	type = vdpasim32_to_cpu(vdpasim, hdr.type);
	sector = vdpasim64_to_cpu(vdpasim, hdr.sector);
	offset = sector << SECTOR_SHIFT;
	status = VIRTIO_BLK_S_OK;

	if (type != VIRTIO_BLK_T_IN && type != VIRTIO_BLK_T_OUT &&
	    sector != 0) {
		dev_dbg(&vdpasim->vdpa.dev,
			"sector must be 0 for %u request - sector: 0x%llx\n",
			type, sector);
		status = VIRTIO_BLK_S_IOERR;
		goto err_status;
	}

	switch (type) {
	case VIRTIO_BLK_T_IN:
		if (!vdpasim_blk_check_range(vdpasim, sector,
					     to_push >> SECTOR_SHIFT,
					     VDPASIM_BLK_SIZE_MAX * VDPASIM_BLK_SEG_MAX)) {
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		vdpasim_blk_buffer_lock(blk);
		bytes = vringh_iov_push_iotlb(&vq->vring, &vq->in_iov,
					      blk->buffer + offset, to_push);
		vdpasim_blk_buffer_unlock(blk);
		if (bytes < 0) {
			dev_dbg(&vdpasim->vdpa.dev,
				"vringh_iov_push_iotlb() error: %zd offset: 0x%llx len: 0x%zx\n",
				bytes, offset, to_push);
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		pushed += bytes;
		break;

	case VIRTIO_BLK_T_OUT:
		if (!vdpasim_blk_check_range(vdpasim, sector,
					     to_pull >> SECTOR_SHIFT,
					     VDPASIM_BLK_SIZE_MAX * VDPASIM_BLK_SEG_MAX)) {
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		vdpasim_blk_buffer_lock(blk);
		bytes = vringh_iov_pull_iotlb(&vq->vring, &vq->out_iov,
					      blk->buffer + offset, to_pull);
		vdpasim_blk_buffer_unlock(blk);
		if (bytes < 0) {
			dev_dbg(&vdpasim->vdpa.dev,
				"vringh_iov_pull_iotlb() error: %zd offset: 0x%llx len: 0x%zx\n",
				bytes, offset, to_pull);
			status = VIRTIO_BLK_S_IOERR;
			break;
		}
		break;

	case VIRTIO_BLK_T_GET_ID:
		bytes = vringh_iov_push_iotlb(&vq->vring, &vq->in_iov,
					      vdpasim_blk_id,
					      VIRTIO_BLK_ID_BYTES);
		if (bytes < 0) {
			dev_dbg(&vdpasim->vdpa.dev,
				"vringh_iov_push_iotlb() error: %zd\n", bytes);
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		pushed += bytes;
		break;

	case VIRTIO_BLK_T_FLUSH:
		/* nothing to do */
		break;

	case VIRTIO_BLK_T_DISCARD:
	case VIRTIO_BLK_T_WRITE_ZEROES: {
		struct virtio_blk_discard_write_zeroes range;
		u32 num_sectors, flags;

		if (to_pull != sizeof(range)) {
			dev_dbg(&vdpasim->vdpa.dev,
				"discard/write_zeroes header len: 0x%zx [expected: 0x%zx]\n",
				to_pull, sizeof(range));
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		bytes = vringh_iov_pull_iotlb(&vq->vring, &vq->out_iov, &range,
					      to_pull);
		if (bytes < 0) {
			dev_dbg(&vdpasim->vdpa.dev,
				"vringh_iov_pull_iotlb() error: %zd offset: 0x%llx len: 0x%zx\n",
				bytes, offset, to_pull);
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		sector = le64_to_cpu(range.sector);
		offset = sector << SECTOR_SHIFT;
		num_sectors = le32_to_cpu(range.num_sectors);
		flags = le32_to_cpu(range.flags);

		if (type == VIRTIO_BLK_T_DISCARD && flags != 0) {
			dev_dbg(&vdpasim->vdpa.dev,
				"discard unexpected flags set - flags: 0x%x\n",
				flags);
			status = VIRTIO_BLK_S_UNSUPP;
			break;
		}

		if (type == VIRTIO_BLK_T_WRITE_ZEROES &&
		    flags & ~VIRTIO_BLK_WRITE_ZEROES_FLAG_UNMAP) {
			dev_dbg(&vdpasim->vdpa.dev,
				"write_zeroes unexpected flags set - flags: 0x%x\n",
				flags);
			status = VIRTIO_BLK_S_UNSUPP;
			break;
		}

		if (!vdpasim_blk_check_range(vdpasim, sector, num_sectors,
					     VDPASIM_BLK_DWZ_MAX_SECTORS)) {
			status = VIRTIO_BLK_S_IOERR;
			break;
		}

		if (type == VIRTIO_BLK_T_WRITE_ZEROES) {
			vdpasim_blk_buffer_lock(blk);
			memset(blk->buffer + offset, 0,
			       num_sectors << SECTOR_SHIFT);
			vdpasim_blk_buffer_unlock(blk);
		}

		break;
	}
	default:
		dev_dbg(&vdpasim->vdpa.dev,
			"Unsupported request type %d\n", type);
		status = VIRTIO_BLK_S_IOERR;
		break;
	}

err_status:
	/* If some operations fail, we need to skip the remaining bytes
	 * to put the status in the last byte
	 */
	if (to_push - pushed > 0)
		vringh_kiov_advance(&vq->in_iov, to_push - pushed);

	/* Last byte is the status */
	bytes = vringh_iov_push_iotlb(&vq->vring, &vq->in_iov, &status, 1);
	if (bytes != 1)
		goto err;

	pushed += bytes;

	/* Make sure data is wrote before advancing index */
	smp_wmb();

	handled = true;

err:
	vringh_complete_iotlb(&vq->vring, vq->head, pushed);

	return handled;
}

static void vdpasim_blk_work(struct vdpasim *vdpasim)
{
	bool reschedule = false;
	int i;

	mutex_lock(&vdpasim->mutex);

	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
		goto out;

	if (!vdpasim->running)
		goto out;

	for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
		struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
		int reqs = 0;

		if (!vq->ready)
			continue;

		while (vdpasim_blk_handle_req(vdpasim, vq)) {
			/* Make sure used is visible before rasing the interrupt. */
			smp_wmb();

			local_bh_disable();
			if (vringh_need_notify_iotlb(&vq->vring) > 0)
				vringh_notify(&vq->vring);
			local_bh_enable();

			if (++reqs > 4) {
				reschedule = true;
				break;
			}
		}
	}
out:
	mutex_unlock(&vdpasim->mutex);

	if (reschedule)
		vdpasim_schedule_work(vdpasim);
}

static void vdpasim_blk_get_config(struct vdpasim *vdpasim, void *config)
{
	struct virtio_blk_config *blk_config = config;

	memset(config, 0, sizeof(struct virtio_blk_config));

	blk_config->capacity = cpu_to_vdpasim64(vdpasim, VDPASIM_BLK_CAPACITY);
	blk_config->size_max = cpu_to_vdpasim32(vdpasim, VDPASIM_BLK_SIZE_MAX);
	blk_config->seg_max = cpu_to_vdpasim32(vdpasim, VDPASIM_BLK_SEG_MAX);
	blk_config->num_queues = cpu_to_vdpasim16(vdpasim, VDPASIM_BLK_VQ_NUM);
	blk_config->min_io_size = cpu_to_vdpasim16(vdpasim, 1);
	blk_config->opt_io_size = cpu_to_vdpasim32(vdpasim, 1);
	blk_config->blk_size = cpu_to_vdpasim32(vdpasim, SECTOR_SIZE);
	/* VIRTIO_BLK_F_DISCARD */
	blk_config->discard_sector_alignment =
		cpu_to_vdpasim32(vdpasim, SECTOR_SIZE);
	blk_config->max_discard_sectors =
		cpu_to_vdpasim32(vdpasim, VDPASIM_BLK_DWZ_MAX_SECTORS);
	blk_config->max_discard_seg = cpu_to_vdpasim32(vdpasim, 1);
	/* VIRTIO_BLK_F_WRITE_ZEROES */
	blk_config->max_write_zeroes_sectors =
		cpu_to_vdpasim32(vdpasim, VDPASIM_BLK_DWZ_MAX_SECTORS);
	blk_config->max_write_zeroes_seg = cpu_to_vdpasim32(vdpasim, 1);

}

static void vdpasim_blk_free(struct vdpasim *vdpasim)
{
	struct vdpasim_blk *blk = sim_to_blk(vdpasim);

	if (!blk->shared_backend)
		kvfree(blk->buffer);
}

static void vdpasim_blk_mgmtdev_release(struct device *dev)
{
}

static struct device vdpasim_blk_mgmtdev = {
	.init_name = "vdpasim_blk",
	.release = vdpasim_blk_mgmtdev_release,
};

static int vdpasim_blk_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
			       const struct vdpa_dev_set_config *config)
{
	struct vdpasim_dev_attr dev_attr = {};
	struct vdpasim_blk *blk;
	struct vdpasim *simdev;
	int ret;

	dev_attr.mgmt_dev = mdev;
	dev_attr.name = name;
	dev_attr.id = VIRTIO_ID_BLOCK;
	dev_attr.supported_features = VDPASIM_BLK_FEATURES;
	dev_attr.nvqs = VDPASIM_BLK_VQ_NUM;
	dev_attr.ngroups = VDPASIM_BLK_GROUP_NUM;
	dev_attr.nas = VDPASIM_BLK_AS_NUM;
	dev_attr.alloc_size = sizeof(struct vdpasim_blk);
	dev_attr.config_size = sizeof(struct virtio_blk_config);
	dev_attr.get_config = vdpasim_blk_get_config;
	dev_attr.work_fn = vdpasim_blk_work;
	dev_attr.free = vdpasim_blk_free;

	simdev = vdpasim_create(&dev_attr, config);
	if (IS_ERR(simdev))
		return PTR_ERR(simdev);

	blk = sim_to_blk(simdev);
	blk->shared_backend = shared_backend;

	if (blk->shared_backend) {
		blk->buffer = shared_buffer;
	} else {
		blk->buffer = kvzalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
				       GFP_KERNEL);
		if (!blk->buffer) {
			ret = -ENOMEM;
			goto put_dev;
		}
	}

	ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_BLK_VQ_NUM);
	if (ret)
		goto put_dev;

	return 0;

put_dev:
	put_device(&simdev->vdpa.dev);
	return ret;
}

static void vdpasim_blk_dev_del(struct vdpa_mgmt_dev *mdev,
				struct vdpa_device *dev)
{
	struct vdpasim *simdev = container_of(dev, struct vdpasim, vdpa);

	_vdpa_unregister_device(&simdev->vdpa);
}

static const struct vdpa_mgmtdev_ops vdpasim_blk_mgmtdev_ops = {
	.dev_add = vdpasim_blk_dev_add,
	.dev_del = vdpasim_blk_dev_del
};

static struct virtio_device_id id_table[] = {
	{ VIRTIO_ID_BLOCK, VIRTIO_DEV_ANY_ID },
	{ 0 },
};

static struct vdpa_mgmt_dev mgmt_dev = {
	.device = &vdpasim_blk_mgmtdev,
	.id_table = id_table,
	.ops = &vdpasim_blk_mgmtdev_ops,
};

static int __init vdpasim_blk_init(void)
{
	int ret;

	ret = device_register(&vdpasim_blk_mgmtdev);
	if (ret) {
		put_device(&vdpasim_blk_mgmtdev);
		return ret;
	}

	ret = vdpa_mgmtdev_register(&mgmt_dev);
	if (ret)
		goto parent_err;

	if (shared_backend) {
		shared_buffer = kvzalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
					 GFP_KERNEL);
		if (!shared_buffer) {
			ret = -ENOMEM;
			goto mgmt_dev_err;
		}
	}

	return 0;
mgmt_dev_err:
	vdpa_mgmtdev_unregister(&mgmt_dev);
parent_err:
	device_unregister(&vdpasim_blk_mgmtdev);
	return ret;
}

static void __exit vdpasim_blk_exit(void)
{
	kvfree(shared_buffer);
	vdpa_mgmtdev_unregister(&mgmt_dev);
	device_unregister(&vdpasim_blk_mgmtdev);
}

module_init(vdpasim_blk_init)
module_exit(vdpasim_blk_exit)

MODULE_VERSION(DRV_VERSION);
MODULE_LICENSE(DRV_LICENSE);
MODULE_AUTHOR(DRV_AUTHOR);
MODULE_DESCRIPTION(DRV_DESC);