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