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 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);