static long ioctl_memcpy()

in fsl_hypervisor.c [147:308]

• 79 lines of code
• 18 McCabe index (conditional complexity)

static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
{
	struct fsl_hv_ioctl_memcpy param;

	struct page **pages = NULL;
	void *sg_list_unaligned = NULL;
	struct fh_sg_list *sg_list = NULL;

	unsigned int num_pages;
	unsigned long lb_offset; /* Offset within a page of the local buffer */

	unsigned int i;
	long ret = 0;
	int num_pinned = 0; /* return value from get_user_pages_fast() */
	phys_addr_t remote_paddr; /* The next address in the remote buffer */
	uint32_t count; /* The number of bytes left to copy */

	/* Get the parameters from the user */
	if (copy_from_user(&param, p, sizeof(struct fsl_hv_ioctl_memcpy)))
		return -EFAULT;

	/*
	 * One partition must be local, the other must be remote.  In other
	 * words, if source and target are both -1, or are both not -1, then
	 * return an error.
	 */
	if ((param.source == -1) == (param.target == -1))
		return -EINVAL;

	/*
	 * The array of pages returned by get_user_pages_fast() covers only
	 * page-aligned memory.  Since the user buffer is probably not
	 * page-aligned, we need to handle the discrepancy.
	 *
	 * We calculate the offset within a page of the S/G list, and make
	 * adjustments accordingly.  This will result in a page list that looks
	 * like this:
	 *
	 *      ----    <-- first page starts before the buffer
	 *     |    |
	 *     |////|-> ----
	 *     |////|  |    |
	 *      ----   |    |
	 *             |    |
	 *      ----   |    |
	 *     |////|  |    |
	 *     |////|  |    |
	 *     |////|  |    |
	 *      ----   |    |
	 *             |    |
	 *      ----   |    |
	 *     |////|  |    |
	 *     |////|  |    |
	 *     |////|  |    |
	 *      ----   |    |
	 *             |    |
	 *      ----   |    |
	 *     |////|  |    |
	 *     |////|-> ----
	 *     |    |   <-- last page ends after the buffer
	 *      ----
	 *
	 * The distance between the start of the first page and the start of the
	 * buffer is lb_offset.  The hashed (///) areas are the parts of the
	 * page list that contain the actual buffer.
	 *
	 * The advantage of this approach is that the number of pages is
	 * equal to the number of entries in the S/G list that we give to the
	 * hypervisor.
	 */
	lb_offset = param.local_vaddr & (PAGE_SIZE - 1);
	if (param.count == 0 ||
	    param.count > U64_MAX - lb_offset - PAGE_SIZE + 1)
		return -EINVAL;
	num_pages = (param.count + lb_offset + PAGE_SIZE - 1) >> PAGE_SHIFT;

	/* Allocate the buffers we need */

	/*
	 * 'pages' is an array of struct page pointers that's initialized by
	 * get_user_pages_fast().
	 */
	pages = kcalloc(num_pages, sizeof(struct page *), GFP_KERNEL);
	if (!pages) {
		pr_debug("fsl-hv: could not allocate page list\n");
		return -ENOMEM;
	}

	/*
	 * sg_list is the list of fh_sg_list objects that we pass to the
	 * hypervisor.
	 */
	sg_list_unaligned = kmalloc(num_pages * sizeof(struct fh_sg_list) +
		sizeof(struct fh_sg_list) - 1, GFP_KERNEL);
	if (!sg_list_unaligned) {
		pr_debug("fsl-hv: could not allocate S/G list\n");
		ret = -ENOMEM;
		goto free_pages;
	}
	sg_list = PTR_ALIGN(sg_list_unaligned, sizeof(struct fh_sg_list));

	/* Get the physical addresses of the source buffer */
	num_pinned = get_user_pages_fast(param.local_vaddr - lb_offset,
		num_pages, param.source != -1 ? FOLL_WRITE : 0, pages);

	if (num_pinned != num_pages) {
		pr_debug("fsl-hv: could not lock source buffer\n");
		ret = (num_pinned < 0) ? num_pinned : -EFAULT;
		goto exit;
	}

	/*
	 * Build the fh_sg_list[] array.  The first page is special
	 * because it's misaligned.
	 */
	if (param.source == -1) {
		sg_list[0].source = page_to_phys(pages[0]) + lb_offset;
		sg_list[0].target = param.remote_paddr;
	} else {
		sg_list[0].source = param.remote_paddr;
		sg_list[0].target = page_to_phys(pages[0]) + lb_offset;
	}
	sg_list[0].size = min_t(uint64_t, param.count, PAGE_SIZE - lb_offset);

	remote_paddr = param.remote_paddr + sg_list[0].size;
	count = param.count - sg_list[0].size;

	for (i = 1; i < num_pages; i++) {
		if (param.source == -1) {
			/* local to remote */
			sg_list[i].source = page_to_phys(pages[i]);
			sg_list[i].target = remote_paddr;
		} else {
			/* remote to local */
			sg_list[i].source = remote_paddr;
			sg_list[i].target = page_to_phys(pages[i]);
		}
		sg_list[i].size = min_t(uint64_t, count, PAGE_SIZE);

		remote_paddr += sg_list[i].size;
		count -= sg_list[i].size;
	}

	param.ret = fh_partition_memcpy(param.source, param.target,
		virt_to_phys(sg_list), num_pages);

exit:
	if (pages && (num_pinned > 0)) {
		for (i = 0; i < num_pinned; i++)
			put_page(pages[i]);
	}

	kfree(sg_list_unaligned);
free_pages:
	kfree(pages);

	if (!ret)
		if (copy_to_user(&p->ret, &param.ret, sizeof(__u32)))
			return -EFAULT;

	return ret;
}