1/*
  2 * Copyright (C) 2015 Synopsys, Inc. (www.synopsys.com)
  3 *
  4 * This program is free software; you can redistribute it and/or modify
  5 * it under the terms of the GNU General Public License version 2 as
  6 * published by the Free Software Foundation.
  7 *
  8 */
  9
 10#include <linux/bootmem.h>
 11#include <linux/export.h>
 12#include <linux/highmem.h>
 13#include <asm/processor.h>
 14#include <asm/pgtable.h>
 15#include <asm/pgalloc.h>
 16#include <asm/tlbflush.h>
 17
 18/*
 19 * HIGHMEM API:
 20 *
 21 * kmap() API provides sleep semantics hence referred to as "permanent maps"
 22 * It allows mapping LAST_PKMAP pages, using @last_pkmap_nr as the cursor
 23 * for book-keeping
 24 *
 25 * kmap_atomic() can't sleep (calls pagefault_disable()), thus it provides
 26 * shortlived ala "temporary mappings" which historically were implemented as
 27 * fixmaps (compile time addr etc). Their book-keeping is done per cpu.
 28 *
 29 *	Both these facts combined (preemption disabled and per-cpu allocation)
 30 *	means the total number of concurrent fixmaps will be limited to max
 31 *	such allocations in a single control path. Thus KM_TYPE_NR (another
 32 *	historic relic) is a small'ish number which caps max percpu fixmaps
 33 *
 34 * ARC HIGHMEM Details
 35 *
 36 * - the kernel vaddr space from 0x7z to 0x8z (currently used by vmalloc/module)
 37 *   is now shared between vmalloc and kmap (non overlapping though)
 38 *
 39 * - Both fixmap/pkmap use a dedicated page table each, hooked up to swapper PGD
 40 *   This means each only has 1 PGDIR_SIZE worth of kvaddr mappings, which means
 41 *   2M of kvaddr space for typical config (8K page and 11:8:13 traversal split)
 42 *
 43 * - fixmap anyhow needs a limited number of mappings. So 2M kvaddr == 256 PTE
 44 *   slots across NR_CPUS would be more than sufficient (generic code defines
 45 *   KM_TYPE_NR as 20).
 46 *
 47 * - pkmap being preemptible, in theory could do with more than 256 concurrent
 48 *   mappings. However, generic pkmap code: map_new_virtual(), doesn't traverse
 49 *   the PGD and only works with a single page table @pkmap_page_table, hence
 50 *   sets the limit
 51 */
 52
 53extern pte_t * pkmap_page_table;
 54static pte_t * fixmap_page_table;
 55
 56void *kmap(struct page *page)
 57{
 58	BUG_ON(in_interrupt());
 59	if (!PageHighMem(page))
 60		return page_address(page);
 61
 62	return kmap_high(page);
 63}
 64EXPORT_SYMBOL(kmap);
 65
 66void *kmap_atomic(struct page *page)
 67{
 68	int idx, cpu_idx;
 69	unsigned long vaddr;
 70
 71	preempt_disable();
 72	pagefault_disable();
 73	if (!PageHighMem(page))
 74		return page_address(page);
 75
 76	cpu_idx = kmap_atomic_idx_push();
 77	idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
 78	vaddr = FIXMAP_ADDR(idx);
 79
 80	set_pte_at(&init_mm, vaddr, fixmap_page_table + idx,
 81		   mk_pte(page, kmap_prot));
 82
 83	return (void *)vaddr;
 84}
 85EXPORT_SYMBOL(kmap_atomic);
 86
 87void __kunmap_atomic(void *kv)
 88{
 89	unsigned long kvaddr = (unsigned long)kv;
 90
 91	if (kvaddr >= FIXMAP_BASE && kvaddr < (FIXMAP_BASE + FIXMAP_SIZE)) {
 92
 93		/*
 94		 * Because preemption is disabled, this vaddr can be associated
 95		 * with the current allocated index.
 96		 * But in case of multiple live kmap_atomic(), it still relies on
 97		 * callers to unmap in right order.
 98		 */
 99		int cpu_idx = kmap_atomic_idx();
100		int idx = cpu_idx + KM_TYPE_NR * smp_processor_id();
101
102		WARN_ON(kvaddr != FIXMAP_ADDR(idx));
103
104		pte_clear(&init_mm, kvaddr, fixmap_page_table + idx);
105		local_flush_tlb_kernel_range(kvaddr, kvaddr + PAGE_SIZE);
106
107		kmap_atomic_idx_pop();
108	}
109
110	pagefault_enable();
111	preempt_enable();
112}
113EXPORT_SYMBOL(__kunmap_atomic);
114
115static noinline pte_t * __init alloc_kmap_pgtable(unsigned long kvaddr)
116{
117	pgd_t *pgd_k;
118	pud_t *pud_k;
119	pmd_t *pmd_k;
120	pte_t *pte_k;
121
122	pgd_k = pgd_offset_k(kvaddr);
123	pud_k = pud_offset(pgd_k, kvaddr);
124	pmd_k = pmd_offset(pud_k, kvaddr);
125
126	pte_k = (pte_t *)alloc_bootmem_low_pages(PAGE_SIZE);
127	pmd_populate_kernel(&init_mm, pmd_k, pte_k);
128	return pte_k;
129}
130
131void __init kmap_init(void)
132{
133	/* Due to recursive include hell, we can't do this in processor.h */
134	BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
135
136	BUILD_BUG_ON(KM_TYPE_NR > PTRS_PER_PTE);
137	pkmap_page_table = alloc_kmap_pgtable(PKMAP_BASE);
138
139	BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
140	fixmap_page_table = alloc_kmap_pgtable(FIXMAP_BASE);
141}