1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/highmem.h>
 3#include <linux/memblock.h>
 4#include <linux/crash_dump.h>
 5#include <linux/uaccess.h>
 6#include <linux/slab.h>
 7
 8static void *kdump_buf_page;
 9
10/**
11 * copy_oldmem_page - copy one page from "oldmem"
12 * @pfn: page frame number to be copied
13 * @buf: target memory address for the copy; this can be in kernel address
14 *	space or user address space (see @userbuf)
15 * @csize: number of bytes to copy
16 * @offset: offset in bytes into the page (based on pfn) to begin the copy
17 * @userbuf: if set, @buf is in user address space, use copy_to_user(),
18 *	otherwise @buf is in kernel address space, use memcpy().
19 *
20 * Copy a page from "oldmem". For this page, there is no pte mapped
21 * in the current kernel.
22 *
23 * Calling copy_to_user() in atomic context is not desirable. Hence first
24 * copying the data to a pre-allocated kernel page and then copying to user
25 * space in non-atomic context.
26 */
27ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
28			 size_t csize, unsigned long offset, int userbuf)
29{
30	void  *vaddr;
31
32	if (!csize)
33		return 0;
34
35	vaddr = kmap_atomic_pfn(pfn);
36
37	if (!userbuf) {
38		memcpy(buf, (vaddr + offset), csize);
39		kunmap_atomic(vaddr);
40	} else {
41		if (!kdump_buf_page) {
42			pr_warn("Kdump: Kdump buffer page not allocated\n");
43
44			return -EFAULT;
45		}
46		copy_page(kdump_buf_page, vaddr);
47		kunmap_atomic(vaddr);
48		if (copy_to_user(buf, (kdump_buf_page + offset), csize))
49			return -EFAULT;
50	}
51
52	return csize;
53}
54
55static int __init kdump_buf_page_init(void)
56{
57	int ret = 0;
58
59	kdump_buf_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
60	if (!kdump_buf_page) {
61		pr_warn("Kdump: Failed to allocate kdump buffer page\n");
62		ret = -ENOMEM;
63	}
64
65	return ret;
66}
67arch_initcall(kdump_buf_page_init);