1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/highmem.h>
 3#include <linux/crash_dump.h>
 4
 5/**
 6 * copy_oldmem_page - copy one page from "oldmem"
 7 * @pfn: page frame number to be copied
 8 * @buf: target memory address for the copy; this can be in kernel address
 9 *	space or user address space (see @userbuf)
10 * @csize: number of bytes to copy
11 * @offset: offset in bytes into the page (based on pfn) to begin the copy
12 * @userbuf: if set, @buf is in user address space, use copy_to_user(),
13 *	otherwise @buf is in kernel address space, use memcpy().
14 *
15 * Copy a page from "oldmem". For this page, there is no pte mapped
16 * in the current kernel.
17 */
18ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
19			 size_t csize, unsigned long offset, int userbuf)
20{
21	void  *vaddr;
22
23	if (!csize)
24		return 0;
25
26	vaddr = kmap_local_pfn(pfn);
27
28	if (!userbuf) {
29		memcpy(buf, vaddr + offset, csize);
30	} else {
31		if (copy_to_user(buf, vaddr + offset, csize))
32			csize = -EFAULT;
33	}
34
35	kunmap_local(vaddr);
36
37	return csize;
38}