1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *	kernel/crash_dump.c - Memory preserving reboot related code.
4  *
5  *	Created by: Simon Horman <horms@verge.net.au>
6  *	Original code moved from kernel/crash.c
7  *	Original code comment copied from the i386 version of this file
8  */
9 
10 #include <linux/errno.h>
11 #include <linux/types.h>
12 #include <linux/crash_dump.h>
13 
14 #include <asm/page.h>
15 #include <linux/uaccess.h>
16 
17 /**
18  * copy_oldmem_page - copy one page from "oldmem"
19  * @pfn: page frame number to be copied
20  * @buf: target memory address for the copy; this can be in kernel address
21  *	space or user address space (see @userbuf)
22  * @csize: number of bytes to copy
23  * @offset: offset in bytes into the page (based on pfn) to begin the copy
24  * @userbuf: if set, @buf is in user address space, use copy_to_user(),
25  *	otherwise @buf is in kernel address space, use memcpy().
26  *
27  * Copy a page from "oldmem". For this page, there is no pte mapped
28  * in the current kernel. We stitch up a pte, similar to kmap_atomic.
29  *
30  * Calling copy_to_user() in atomic context is not desirable. Hence first
31  * copying the data to a pre-allocated kernel page and then copying to user
32  * space in non-atomic context.
33  */
34 ssize_t
copy_oldmem_page(unsigned long pfn,char * buf,size_t csize,unsigned long offset,int userbuf)35 copy_oldmem_page(unsigned long pfn, char *buf,
36 		size_t csize, unsigned long offset, int userbuf)
37 {
38 	void  *vaddr;
39 
40 	if (!csize)
41 		return 0;
42 	vaddr = __va(pfn<<PAGE_SHIFT);
43 	if (userbuf) {
44 		if (copy_to_user(buf, (vaddr + offset), csize)) {
45 			return -EFAULT;
46 		}
47 	} else
48 		memcpy(buf, (vaddr + offset), csize);
49 	return csize;
50 }
51 
52