// SPDX-License-Identifier: GPL-2.0
#include <linux/cred.h>
#include <linux/device.h>
#include <linux/dma-buf.h>
#include <linux/dma-resv.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/memfd.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/shmem_fs.h>
#include <linux/hugetlb.h>
#include <linux/slab.h>
#include <linux/udmabuf.h>
#include <linux/vmalloc.h>
#include <linux/iosys-map.h>

static int list_limit = 1024;
module_param(list_limit, int, 0644);
MODULE_PARM_DESC(list_limit, "udmabuf_create_list->count limit. Default is 1024.");

static int size_limit_mb = 64;
module_param(size_limit_mb, int, 0644);
MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is 64.");

struct udmabuf {
	pgoff_t pagecount;
	struct folio **folios;
	struct sg_table *sg;
	struct miscdevice *device;
	pgoff_t *offsets;
};

static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
{
	struct vm_area_struct *vma = vmf->vma;
	struct udmabuf *ubuf = vma->vm_private_data;
	pgoff_t pgoff = vmf->pgoff;
	unsigned long pfn;

	if (pgoff >= ubuf->pagecount)
		return VM_FAULT_SIGBUS;

	pfn = folio_pfn(ubuf->folios[pgoff]);
	pfn += ubuf->offsets[pgoff] >> PAGE_SHIFT;

	return vmf_insert_pfn(vma, vmf->address, pfn);
}

static const struct vm_operations_struct udmabuf_vm_ops = {
	.fault = udmabuf_vm_fault,
};

static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
{
	struct udmabuf *ubuf = buf->priv;

	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
		return -EINVAL;

	vma->vm_ops = &udmabuf_vm_ops;
	vma->vm_private_data = ubuf;
	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
	return 0;
}

static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
{
	struct udmabuf *ubuf = buf->priv;
	unsigned long *pfns;
	void *vaddr;
	pgoff_t pg;

	dma_resv_assert_held(buf->resv);

	/**
	 * HVO may free tail pages, so just use pfn to map each folio
	 * into vmalloc area.
	 */
	pfns = kvmalloc_array(ubuf->pagecount, sizeof(*pfns), GFP_KERNEL);
	if (!pfns)
		return -ENOMEM;

	for (pg = 0; pg < ubuf->pagecount; pg++) {
		unsigned long pfn = folio_pfn(ubuf->folios[pg]);

		pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
		pfns[pg] = pfn;
	}

	vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
	kvfree(pfns);
	if (!vaddr)
		return -EINVAL;

	iosys_map_set_vaddr(map, vaddr);
	return 0;
}

static void vunmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
{
	struct udmabuf *ubuf = buf->priv;

	dma_resv_assert_held(buf->resv);

	vm_unmap_ram(map->vaddr, ubuf->pagecount);
}

static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
				     enum dma_data_direction direction)
{
	struct udmabuf *ubuf = buf->priv;
	struct sg_table *sg;
	struct scatterlist *sgl;
	unsigned int i = 0;
	int ret;

	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
	if (!sg)
		return ERR_PTR(-ENOMEM);

	ret = sg_alloc_table(sg, ubuf->pagecount, GFP_KERNEL);
	if (ret < 0)
		goto err_alloc;

	for_each_sg(sg->sgl, sgl, ubuf->pagecount, i)
		sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
			     ubuf->offsets[i]);

	ret = dma_map_sgtable(dev, sg, direction, 0);
	if (ret < 0)
		goto err_map;
	return sg;

err_map:
	sg_free_table(sg);
err_alloc:
	kfree(sg);
	return ERR_PTR(ret);
}

static void put_sg_table(struct device *dev, struct sg_table *sg,
			 enum dma_data_direction direction)
{
	dma_unmap_sgtable(dev, sg, direction, 0);
	sg_free_table(sg);
	kfree(sg);
}

static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
				    enum dma_data_direction direction)
{
	return get_sg_table(at->dev, at->dmabuf, direction);
}

static void unmap_udmabuf(struct dma_buf_attachment *at,
			  struct sg_table *sg,
			  enum dma_data_direction direction)
{
	return put_sg_table(at->dev, sg, direction);
}

static void release_udmabuf(struct dma_buf *buf)
{
	struct udmabuf *ubuf = buf->priv;
	struct device *dev = ubuf->device->this_device;
	pgoff_t pg;

	if (ubuf->sg)
		put_sg_table(dev, ubuf->sg, DMA_BIDIRECTIONAL);

	for (pg = 0; pg < ubuf->pagecount; pg++)
		folio_put(ubuf->folios[pg]);
	kvfree(ubuf->offsets);
	kvfree(ubuf->folios);
	kfree(ubuf);
}

static int begin_cpu_udmabuf(struct dma_buf *buf,
			     enum dma_data_direction direction)
{
	struct udmabuf *ubuf = buf->priv;
	struct device *dev = ubuf->device->this_device;
	int ret = 0;

	if (!ubuf->sg) {
		ubuf->sg = get_sg_table(dev, buf, direction);
		if (IS_ERR(ubuf->sg)) {
			ret = PTR_ERR(ubuf->sg);
			ubuf->sg = NULL;
		}
	} else {
		dma_sync_sg_for_cpu(dev, ubuf->sg->sgl, ubuf->sg->nents,
				    direction);
	}

	return ret;
}

static int end_cpu_udmabuf(struct dma_buf *buf,
			   enum dma_data_direction direction)
{
	struct udmabuf *ubuf = buf->priv;
	struct device *dev = ubuf->device->this_device;

	if (!ubuf->sg)
		return -EINVAL;

	dma_sync_sg_for_device(dev, ubuf->sg->sgl, ubuf->sg->nents, direction);
	return 0;
}

static const struct dma_buf_ops udmabuf_ops = {
	.cache_sgt_mapping = true,
	.map_dma_buf	   = map_udmabuf,
	.unmap_dma_buf	   = unmap_udmabuf,
	.release	   = release_udmabuf,
	.mmap		   = mmap_udmabuf,
	.vmap		   = vmap_udmabuf,
	.vunmap		   = vunmap_udmabuf,
	.begin_cpu_access  = begin_cpu_udmabuf,
	.end_cpu_access    = end_cpu_udmabuf,
};

#define SEALS_WANTED (F_SEAL_SHRINK)
#define SEALS_DENIED (F_SEAL_WRITE|F_SEAL_FUTURE_WRITE)

static int handle_hugetlb_pages(struct udmabuf *ubuf, struct file *memfd,
				pgoff_t offset, pgoff_t pgcnt,
				pgoff_t *pgbuf)
{
	struct hstate *hpstate = hstate_file(memfd);
	pgoff_t mapidx = offset >> huge_page_shift(hpstate);
	pgoff_t subpgoff = (offset & ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
	pgoff_t maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
	struct folio *folio = NULL;
	pgoff_t pgidx;

	mapidx <<= huge_page_order(hpstate);
	for (pgidx = 0; pgidx < pgcnt; pgidx++) {
		if (!folio) {
			folio = __filemap_get_folio(memfd->f_mapping,
						    mapidx,
						    FGP_ACCESSED, 0);
			if (IS_ERR(folio))
				return PTR_ERR(folio);
		}

		folio_get(folio);
		ubuf->folios[*pgbuf] = folio;
		ubuf->offsets[*pgbuf] = subpgoff << PAGE_SHIFT;
		(*pgbuf)++;
		if (++subpgoff == maxsubpgs) {
			folio_put(folio);
			folio = NULL;
			subpgoff = 0;
			mapidx += pages_per_huge_page(hpstate);
		}
	}

	if (folio)
		folio_put(folio);

	return 0;
}

static int handle_shmem_pages(struct udmabuf *ubuf, struct file *memfd,
			      pgoff_t offset, pgoff_t pgcnt,
			      pgoff_t *pgbuf)
{
	pgoff_t pgidx, pgoff = offset >> PAGE_SHIFT;
	struct folio *folio = NULL;

	for (pgidx = 0; pgidx < pgcnt; pgidx++) {
		folio = shmem_read_folio(memfd->f_mapping, pgoff + pgidx);
		if (IS_ERR(folio))
			return PTR_ERR(folio);

		ubuf->folios[*pgbuf] = folio;
		(*pgbuf)++;
	}

	return 0;
}

static int check_memfd_seals(struct file *memfd)
{
	int seals;

	if (!memfd)
		return -EBADFD;

	if (!shmem_file(memfd) && !is_file_hugepages(memfd))
		return -EBADFD;

	seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
	if (seals == -EINVAL)
		return -EBADFD;

	if ((seals & SEALS_WANTED) != SEALS_WANTED ||
	    (seals & SEALS_DENIED) != 0)
		return -EINVAL;

	return 0;
}

static struct dma_buf *export_udmabuf(struct udmabuf *ubuf,
				      struct miscdevice *device)
{
	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);

	ubuf->device = device;
	exp_info.ops  = &udmabuf_ops;
	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
	exp_info.priv = ubuf;
	exp_info.flags = O_RDWR;

	return dma_buf_export(&exp_info);
}

static long udmabuf_create(struct miscdevice *device,
			   struct udmabuf_create_list *head,
			   struct udmabuf_create_item *list)
{
	pgoff_t pgcnt, pgbuf = 0, pglimit;
	struct file *memfd = NULL;
	struct udmabuf *ubuf;
	struct dma_buf *dmabuf;
	int ret = -EINVAL;
	u32 i, flags;

	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
	if (!ubuf)
		return -ENOMEM;

	pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
	for (i = 0; i < head->count; i++) {
		if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
			goto err;
		if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
			goto err;
		ubuf->pagecount += list[i].size >> PAGE_SHIFT;
		if (ubuf->pagecount > pglimit)
			goto err;
	}

	if (!ubuf->pagecount)
		goto err;

	ubuf->folios = kvmalloc_array(ubuf->pagecount, sizeof(*ubuf->folios),
				      GFP_KERNEL);
	if (!ubuf->folios) {
		ret = -ENOMEM;
		goto err;
	}
	ubuf->offsets = kvcalloc(ubuf->pagecount, sizeof(*ubuf->offsets),
				 GFP_KERNEL);
	if (!ubuf->offsets) {
		ret = -ENOMEM;
		goto err;
	}

	pgbuf = 0;
	for (i = 0; i < head->count; i++) {
		memfd = fget(list[i].memfd);
		ret = check_memfd_seals(memfd);
		if (ret < 0)
			goto err;

		pgcnt = list[i].size >> PAGE_SHIFT;
		if (is_file_hugepages(memfd))
			ret = handle_hugetlb_pages(ubuf, memfd,
						   list[i].offset,
						   pgcnt, &pgbuf);
		else
			ret = handle_shmem_pages(ubuf, memfd,
						 list[i].offset,
						 pgcnt, &pgbuf);
		if (ret < 0)
			goto err;

		fput(memfd);
		memfd = NULL;
	}

	flags = head->flags & UDMABUF_FLAGS_CLOEXEC ? O_CLOEXEC : 0;
	dmabuf = export_udmabuf(ubuf, device);
	if (IS_ERR(dmabuf)) {
		ret = PTR_ERR(dmabuf);
		goto err;
	}
	/*
	 * Ownership of ubuf is held by the dmabuf from here.
	 * If the following dma_buf_fd() fails, dma_buf_put() cleans up both the
	 * dmabuf and the ubuf (through udmabuf_ops.release).
	 */

	ret = dma_buf_fd(dmabuf, flags);
	if (ret < 0)
		dma_buf_put(dmabuf);

	return ret;

err:
	while (pgbuf > 0)
		folio_put(ubuf->folios[--pgbuf]);
	if (memfd)
		fput(memfd);
	kvfree(ubuf->offsets);
	kvfree(ubuf->folios);
	kfree(ubuf);
	return ret;
}

static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
{
	struct udmabuf_create create;
	struct udmabuf_create_list head;
	struct udmabuf_create_item list;

	if (copy_from_user(&create, (void __user *)arg,
			   sizeof(create)))
		return -EFAULT;

	head.flags  = create.flags;
	head.count  = 1;
	list.memfd  = create.memfd;
	list.offset = create.offset;
	list.size   = create.size;

	return udmabuf_create(filp->private_data, &head, &list);
}

static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
{
	struct udmabuf_create_list head;
	struct udmabuf_create_item *list;
	int ret = -EINVAL;
	u32 lsize;

	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
		return -EFAULT;
	if (head.count > list_limit)
		return -EINVAL;
	lsize = sizeof(struct udmabuf_create_item) * head.count;
	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
	if (IS_ERR(list))
		return PTR_ERR(list);

	ret = udmabuf_create(filp->private_data, &head, list);
	kfree(list);
	return ret;
}

static long udmabuf_ioctl(struct file *filp, unsigned int ioctl,
			  unsigned long arg)
{
	long ret;

	switch (ioctl) {
	case UDMABUF_CREATE:
		ret = udmabuf_ioctl_create(filp, arg);
		break;
	case UDMABUF_CREATE_LIST:
		ret = udmabuf_ioctl_create_list(filp, arg);
		break;
	default:
		ret = -ENOTTY;
		break;
	}
	return ret;
}

static const struct file_operations udmabuf_fops = {
	.owner		= THIS_MODULE,
	.unlocked_ioctl = udmabuf_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl   = udmabuf_ioctl,
#endif
};

static struct miscdevice udmabuf_misc = {
	.minor          = MISC_DYNAMIC_MINOR,
	.name           = "udmabuf",
	.fops           = &udmabuf_fops,
};

static int __init udmabuf_dev_init(void)
{
	int ret;

	ret = misc_register(&udmabuf_misc);
	if (ret < 0) {
		pr_err("Could not initialize udmabuf device\n");
		return ret;
	}

	ret = dma_coerce_mask_and_coherent(udmabuf_misc.this_device,
					   DMA_BIT_MASK(64));
	if (ret < 0) {
		pr_err("Could not setup DMA mask for udmabuf device\n");
		misc_deregister(&udmabuf_misc);
		return ret;
	}

	return 0;
}

static void __exit udmabuf_dev_exit(void)
{
	misc_deregister(&udmabuf_misc);
}

module_init(udmabuf_dev_init)
module_exit(udmabuf_dev_exit)

MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");