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Linux/arch/arc/mm/highmem.c

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  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 }
142 

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