arch/arc/mm/highmem.c

   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
  53 extern pte_t * pkmap_page_table;
  54 static pte_t * fixmap_page_table;
  55
  56 void *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 }
  64 EXPORT_SYMBOL(kmap);
  65
  66 void *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 }
  85 EXPORT_SYMBOL(kmap_atomic);
  86
  87 void __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 }
 113 EXPORT_SYMBOL(__kunmap_atomic);
 114
 115 static 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
 131 void __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 }