1 // SPDX-License-Identifier: GPL-2.0
3 * This code is used on x86_64 to create page table identity mappings on
4 * demand by building up a new set of page tables (or appending to the
5 * existing ones), and then switching over to them when ready.
7 * Copyright (C) 2015-2016 Yinghai Lu
8 * Copyright (C) 2016 Kees Cook
12 * Since we're dealing with identity mappings, physical and virtual
13 * addresses are the same, so override these defines which are ultimately
14 * used by the headers in misc.h.
16 #define __pa(x) ((unsigned long)(x))
17 #define __va(x) ((void *)((unsigned long)(x)))
20 * The pgtable.h and mm/ident_map.c includes make use of the SME related
21 * information which is not used in the compressed image support. Un-define
22 * the SME support to avoid any compile and link errors.
24 #undef CONFIG_AMD_MEM_ENCRYPT
26 /* No PAGE_TABLE_ISOLATION support needed either: */
27 #undef CONFIG_PAGE_TABLE_ISOLATION
31 /* These actually do the work of building the kernel identity maps. */
33 #include <asm/pgtable.h>
34 /* Use the static base for this part of the boot process */
36 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
37 #include "../../mm/ident_map.c"
39 /* Used by pgtable.h asm code to force instruction serialization. */
40 unsigned long __force_order
;
42 /* Used to track our page table allocation area. */
43 struct alloc_pgt_data
{
44 unsigned char *pgt_buf
;
45 unsigned long pgt_buf_size
;
46 unsigned long pgt_buf_offset
;
50 * Allocates space for a page table entry, using struct alloc_pgt_data
51 * above. Besides the local callers, this is used as the allocation
52 * callback in mapping_info below.
54 static void *alloc_pgt_page(void *context
)
56 struct alloc_pgt_data
*pages
= (struct alloc_pgt_data
*)context
;
59 /* Validate there is space available for a new page. */
60 if (pages
->pgt_buf_offset
>= pages
->pgt_buf_size
) {
61 debug_putstr("out of pgt_buf in " __FILE__
"!?\n");
62 debug_putaddr(pages
->pgt_buf_offset
);
63 debug_putaddr(pages
->pgt_buf_size
);
67 entry
= pages
->pgt_buf
+ pages
->pgt_buf_offset
;
68 pages
->pgt_buf_offset
+= PAGE_SIZE
;
73 /* Used to track our allocated page tables. */
74 static struct alloc_pgt_data pgt_data
;
76 /* The top level page table entry pointer. */
77 static unsigned long top_level_pgt
;
80 * Mapping information structure passed to kernel_ident_mapping_init().
81 * Due to relocation, pointers must be assigned at run time not build time.
83 static struct x86_mapping_info mapping_info
= {
84 .page_flag
= __PAGE_KERNEL_LARGE_EXEC
,
87 /* Locates and clears a region for a new top level page table. */
88 void initialize_identity_maps(void)
90 /* Init mapping_info with run-time function/buffer pointers. */
91 mapping_info
.alloc_pgt_page
= alloc_pgt_page
;
92 mapping_info
.context
= &pgt_data
;
95 * It should be impossible for this not to already be true,
96 * but since calling this a second time would rewind the other
97 * counters, let's just make sure this is reset too.
99 pgt_data
.pgt_buf_offset
= 0;
102 * If we came here via startup_32(), cr3 will be _pgtable already
103 * and we must append to the existing area instead of entirely
106 * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
107 * the top-level page table is allocated separately.
109 * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
110 * cases. On 4-level paging it's equal to 'top_level_pgt'.
112 top_level_pgt
= read_cr3_pa();
113 if (p4d_offset((pgd_t
*)top_level_pgt
, 0) == (p4d_t
*)_pgtable
) {
114 debug_putstr("booted via startup_32()\n");
115 pgt_data
.pgt_buf
= _pgtable
+ BOOT_INIT_PGT_SIZE
;
116 pgt_data
.pgt_buf_size
= BOOT_PGT_SIZE
- BOOT_INIT_PGT_SIZE
;
117 memset(pgt_data
.pgt_buf
, 0, pgt_data
.pgt_buf_size
);
119 debug_putstr("booted via startup_64()\n");
120 pgt_data
.pgt_buf
= _pgtable
;
121 pgt_data
.pgt_buf_size
= BOOT_PGT_SIZE
;
122 memset(pgt_data
.pgt_buf
, 0, pgt_data
.pgt_buf_size
);
123 top_level_pgt
= (unsigned long)alloc_pgt_page(&pgt_data
);
128 * Adds the specified range to what will become the new identity mappings.
129 * Once all ranges have been added, the new mapping is activated by calling
130 * finalize_identity_maps() below.
132 void add_identity_map(unsigned long start
, unsigned long size
)
134 unsigned long end
= start
+ size
;
136 /* Align boundary to 2M. */
137 start
= round_down(start
, PMD_SIZE
);
138 end
= round_up(end
, PMD_SIZE
);
142 /* Build the mapping. */
143 kernel_ident_mapping_init(&mapping_info
, (pgd_t
*)top_level_pgt
,
148 * This switches the page tables to the new level4 that has been built
149 * via calls to add_identity_map() above. If booted via startup_32(),
150 * this is effectively a no-op.
152 void finalize_identity_maps(void)
154 write_cr3(top_level_pgt
);