arch/x86/kernel/crash_dump_32.c

   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 inline bool is_crashed_pfn_valid(unsigned long pfn)
  17 {
  18 #ifndef CONFIG_X86_PAE
  19         /*
  20          * non-PAE kdump kernel executed from a PAE one will crop high pte
  21          * bits and poke unwanted space counting again from address 0, we
  22          * don't want that. pte must fit into unsigned long. In fact the
  23          * test checks high 12 bits for being zero (pfn will be shifted left
  24          * by PAGE_SHIFT).
  25          */
  26         return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
  27 #else
  28         return true;
  29 #endif
  30 }
  31
  32 /**
  33  * copy_oldmem_page - copy one page from "oldmem"
  34  * @pfn: page frame number to be copied
  35  * @buf: target memory address for the copy; this can be in kernel address
  36  *      space or user address space (see @userbuf)
  37  * @csize: number of bytes to copy
  38  * @offset: offset in bytes into the page (based on pfn) to begin the copy
  39  * @userbuf: if set, @buf is in user address space, use copy_to_user(),
  40  *      otherwise @buf is in kernel address space, use memcpy().
  41  *
  42  * Copy a page from "oldmem". For this page, there might be no pte mapped
  43  * in the current kernel.
  44  */
  45 ssize_t copy_oldmem_page(unsigned long pfn, char *buf, size_t csize,
  46                          unsigned long offset, int userbuf)
  47 {
  48         void  *vaddr;
  49
  50         if (!csize)
  51                 return 0;
  52
  53         if (!is_crashed_pfn_valid(pfn))
  54                 return -EFAULT;
  55
  56         vaddr = kmap_local_pfn(pfn);
  57
  58         if (!userbuf) {
  59                 memcpy(buf, vaddr + offset, csize);
  60         } else {
  61                 if (copy_to_user(buf, vaddr + offset, csize))
  62                         csize = -EFAULT;
  63         }
  64
  65         kunmap_local(vaddr);
  66
  67         return csize;
  68 }