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