1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2015 Synopsys, Inc. (www.synopsys.com)
4 */
5
6 #include <linux/memblock.h>
7 #include <linux/export.h>
8 #include <linux/highmem.h>
9 #include <linux/pgtable.h>
10 #include <asm/processor.h>
11 #include <asm/pgalloc.h>
12 #include <asm/tlbflush.h>
13
14 /*
15 * HIGHMEM API:
16 *
17 * kmap() API provides sleep semantics hence referred to as "permanent maps"
18 * It allows mapping LAST_PKMAP pages, using @last_pkmap_nr as the cursor
19 * for book-keeping
20 *
21 * kmap_atomic() can't sleep (calls pagefault_disable()), thus it provides
22 * shortlived ala "temporary mappings" which historically were implemented as
23 * fixmaps (compile time addr etc). Their book-keeping is done per cpu.
24 *
25 * Both these facts combined (preemption disabled and per-cpu allocation)
26 * means the total number of concurrent fixmaps will be limited to max
27 * such allocations in a single control path. Thus KM_TYPE_NR (another
28 * historic relic) is a small'ish number which caps max percpu fixmaps
29 *
30 * ARC HIGHMEM Details
31 *
32 * - the kernel vaddr space from 0x7z to 0x8z (currently used by vmalloc/module)
33 * is now shared between vmalloc and kmap (non overlapping though)
34 *
35 * - Both fixmap/pkmap use a dedicated page table each, hooked up to swapper PGD
36 * This means each only has 1 PGDIR_SIZE worth of kvaddr mappings, which means
37 * 2M of kvaddr space for typical config (8K page and 11:8:13 traversal split)
38 *
39 * - The fixed KMAP slots for kmap_local/atomic() require KM_MAX_IDX slots per
40 * CPU. So the number of CPUs sharing a single PTE page is limited.
41 *
42 * - pkmap being preemptible, in theory could do with more than 256 concurrent
43 * mappings. However, generic pkmap code: map_new_virtual(), doesn't traverse
44 * the PGD and only works with a single page table @pkmap_page_table, hence
45 * sets the limit
46 */
47
48 extern pte_t * pkmap_page_table;
49
50 static noinline pte_t * __init alloc_kmap_pgtable(unsigned long kvaddr)
51 {
52 pmd_t *pmd_k = pmd_off_k(kvaddr);
53 pte_t *pte_k;
54
55 pte_k = (pte_t *)memblock_alloc_low(PAGE_SIZE, PAGE_SIZE);
56 if (!pte_k)
57 panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
58 __func__, PAGE_SIZE, PAGE_SIZE);
59
60 pmd_populate_kernel(&init_mm, pmd_k, pte_k);
61 return pte_k;
62 }
63
64 void __init kmap_init(void)
65 {
66 /* Due to recursive include hell, we can't do this in processor.h */
67 BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
68 BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
69 BUILD_BUG_ON(FIX_KMAP_SLOTS > PTRS_PER_PTE);
70
71 pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE);
72 alloc_kmap_pgtable(FIXMAP_BASE);
73 }
74
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