1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Memory preserving reboot related code. 4 * 5 * Created by: Hariprasad Nellitheertha (hari@in.ibm.com) 6 * Copyright (C) IBM Corporation, 2004. All rights reserved 7 */ 8 9 #include <linux/slab.h> 10 #include <linux/errno.h> 11 #include <linux/highmem.h> 12 #include <linux/crash_dump.h> 13 14 #include <linux/uaccess.h> 15 16 static void *kdump_buf_page; 17 18 static inline bool is_crashed_pfn_valid(unsigned long pfn) 19 { 20 #ifndef CONFIG_X86_PAE 21 /* 22 * non-PAE kdump kernel executed from a PAE one will crop high pte 23 * bits and poke unwanted space counting again from address 0, we 24 * don't want that. pte must fit into unsigned long. In fact the 25 * test checks high 12 bits for being zero (pfn will be shifted left 26 * by PAGE_SHIFT). 27 */ 28 return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn; 29 #else 30 return true; 31 #endif 32 } 33 34 /** 35 * copy_oldmem_page - copy one page from "oldmem" 36 * @pfn: page frame number to be copied 37 * @buf: target memory address for the copy; this can be in kernel address 38 * space or user address space (see @userbuf) 39 * @csize: number of bytes to copy 40 * @offset: offset in bytes into the page (based on pfn) to begin the copy 41 * @userbuf: if set, @buf is in user address space, use copy_to_user(), 42 * otherwise @buf is in kernel address space, use memcpy(). 43 * 44 * Copy a page from "oldmem". For this page, there is no pte mapped 45 * in the current kernel. We stitch up a pte, similar to kmap_atomic. 46 * 47 * Calling copy_to_user() in atomic context is not desirable. Hence first 48 * copying the data to a pre-allocated kernel page and then copying to user 49 * space in non-atomic context. 50 */ 51 ssize_t copy_oldmem_page(unsigned long pfn, char *buf, 52 size_t csize, unsigned long offset, int userbuf) 53 { 54 void *vaddr; 55 56 if (!csize) 57 return 0; 58 59 if (!is_crashed_pfn_valid(pfn)) 60 return -EFAULT; 61 62 vaddr = kmap_atomic_pfn(pfn); 63 64 if (!userbuf) { 65 memcpy(buf, (vaddr + offset), csize); 66 kunmap_atomic(vaddr); 67 } else { 68 if (!kdump_buf_page) { 69 printk(KERN_WARNING "Kdump: Kdump buffer page not" 70 " allocated\n"); 71 kunmap_atomic(vaddr); 72 return -EFAULT; 73 } 74 copy_page(kdump_buf_page, vaddr); 75 kunmap_atomic(vaddr); 76 if (copy_to_user(buf, (kdump_buf_page + offset), csize)) 77 return -EFAULT; 78 } 79 80 return csize; 81 } 82 83 static int __init kdump_buf_page_init(void) 84 { 85 int ret = 0; 86 87 kdump_buf_page = kmalloc(PAGE_SIZE, GFP_KERNEL); 88 if (!kdump_buf_page) { 89 printk(KERN_WARNING "Kdump: Failed to allocate kdump buffer" 90 " page\n"); 91 ret = -ENOMEM; 92 } 93 94 return ret; 95 } 96 arch_initcall(kdump_buf_page_init); 97