arch/arm/mm/minicache.c

   1 /*
   2  *  linux/arch/arm/mm/minicache.c
   3  *
   4  *  Copyright (C) 2001 Russell King
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * This handles the mini data cache, as found on SA11x0 and XScale
  11  * processors.  When we copy a user page page, we map it in such a way
  12  * that accesses to this page will not touch the main data cache, but
  13  * will be cached in the mini data cache.  This prevents us thrashing
  14  * the main data cache on page faults.
  15  */
  16 #include <linux/init.h>
  17 #include <linux/mm.h>
  18
  19 #include <asm/page.h>
  20 #include <asm/pgtable.h>
  21 #include <asm/tlbflush.h>
  22
  23 /*
  24  * 0xffff8000 to 0xffffffff is reserved for any ARM architecture
  25  * specific hacks for copying pages efficiently.
  26  */
  27 #define minicache_address (0xffff8000)
  28 #define minicache_pgprot __pgprot(L_PTE_PRESENT | L_PTE_YOUNG | \
  29                                   L_PTE_CACHEABLE)
  30
  31 static pte_t *minicache_pte;
  32
  33 /*
  34  * Note that this is intended to be called only from the copy_user_page
  35  * asm code; anything else will require special locking to prevent the
  36  * mini-cache space being re-used.  (Note: probably preempt unsafe).
  37  *
  38  * We rely on the fact that the minicache is 2K, and we'll be pushing
  39  * 4K of data through it, so we don't actually have to specifically
  40  * flush the minicache when we change the mapping.
  41  *
  42  * Note also: assert(PAGE_OFFSET <= virt < high_memory).
  43  * Unsafe: preempt, kmap.
  44  */
  45 unsigned long map_page_minicache(unsigned long virt)
  46 {
  47         set_pte(minicache_pte, pfn_pte(__pa(virt) >> PAGE_SHIFT, minicache_pgprot));
  48         flush_tlb_kernel_page(minicache_address);
  49
  50         return minicache_address;
  51 }
  52
  53 static int __init minicache_init(void)
  54 {
  55         pgd_t *pgd;
  56         pmd_t *pmd;
  57
  58         spin_lock(&init_mm.page_table_lock);
  59
  60         pgd = pgd_offset_k(minicache_address);
  61         pmd = pmd_alloc(&init_mm, pgd, minicache_address);
  62         if (!pmd)
  63                 BUG();
  64         minicache_pte = pte_alloc_kernel(&init_mm, pmd, minicache_address);
  65         if (!minicache_pte)
  66                 BUG();
  67
  68         spin_unlock(&init_mm.page_table_lock);
  69
  70         return 0;
  71 }
  72
  73 core_initcall(minicache_init);