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
48extern pte_t * pkmap_page_table;
49
50static 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
64void __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