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fault-armv.c

/*
 *  linux/arch/arm/mm/fault-armv.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Modifications for ARM processor (c) 1995-2002 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/bitops.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/pagemap.h>

#include <asm/cacheflush.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>

static unsigned long shared_pte_mask = L_PTE_CACHEABLE;

/*
 * We take the easy way out of this problem - we make the
 * PTE uncacheable.  However, we leave the write buffer on.
 *
 * Note that the pte lock held when calling update_mmu_cache must also
 * guard the pte (somewhere else in the same mm) that we modify here.
 * Therefore those configurations which might call adjust_pte (those
 * without CONFIG_CPU_CACHE_VIPT) cannot support split page_table_lock.
 */
static int adjust_pte(struct vm_area_struct *vma, unsigned long address)
{
      pgd_t *pgd;
      pmd_t *pmd;
      pte_t *pte, entry;
      int ret;

      pgd = pgd_offset(vma->vm_mm, address);
      if (pgd_none(*pgd))
            goto no_pgd;
      if (pgd_bad(*pgd))
            goto bad_pgd;

      pmd = pmd_offset(pgd, address);
      if (pmd_none(*pmd))
            goto no_pmd;
      if (pmd_bad(*pmd))
            goto bad_pmd;

      pte = pte_offset_map(pmd, address);
      entry = *pte;

      /*
       * If this page is present, it's actually being shared.
       */
      ret = pte_present(entry);

      /*
       * If this page isn't present, or is already setup to
       * fault (ie, is old), we can safely ignore any issues.
       */
      if (ret && pte_val(entry) & shared_pte_mask) {
            flush_cache_page(vma, address, pte_pfn(entry));
            pte_val(entry) &= ~shared_pte_mask;
            set_pte_at(vma->vm_mm, address, pte, entry);
            flush_tlb_page(vma, address);
      }
      pte_unmap(pte);
      return ret;

bad_pgd:
      pgd_ERROR(*pgd);
      pgd_clear(pgd);
no_pgd:
      return 0;

bad_pmd:
      pmd_ERROR(*pmd);
      pmd_clear(pmd);
no_pmd:
      return 0;
}

static void
make_coherent(struct address_space *mapping, struct vm_area_struct *vma, unsigned long addr, unsigned long pfn)
{
      struct mm_struct *mm = vma->vm_mm;
      struct vm_area_struct *mpnt;
      struct prio_tree_iter iter;
      unsigned long offset;
      pgoff_t pgoff;
      int aliases = 0;

      pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);

      /*
       * If we have any shared mappings that are in the same mm
       * space, then we need to handle them specially to maintain
       * cache coherency.
       */
      flush_dcache_mmap_lock(mapping);
      vma_prio_tree_foreach(mpnt, &iter, &mapping->i_mmap, pgoff, pgoff) {
            /*
             * If this VMA is not in our MM, we can ignore it.
             * Note that we intentionally mask out the VMA
             * that we are fixing up.
             */
            if (mpnt->vm_mm != mm || mpnt == vma)
                  continue;
            if (!(mpnt->vm_flags & VM_MAYSHARE))
                  continue;
            offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
            aliases += adjust_pte(mpnt, mpnt->vm_start + offset);
      }
      flush_dcache_mmap_unlock(mapping);
      if (aliases)
            adjust_pte(vma, addr);
      else
            flush_cache_page(vma, addr, pfn);
}

/*
 * Take care of architecture specific things when placing a new PTE into
 * a page table, or changing an existing PTE.  Basically, there are two
 * things that we need to take care of:
 *
 *  1. If PG_dcache_dirty is set for the page, we need to ensure
 *     that any cache entries for the kernels virtual memory
 *     range are written back to the page.
 *  2. If we have multiple shared mappings of the same space in
 *     an object, we need to deal with the cache aliasing issues.
 *
 * Note that the pte lock will be held.
 */
void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
{
      unsigned long pfn = pte_pfn(pte);
      struct address_space *mapping;
      struct page *page;

      if (!pfn_valid(pfn))
            return;

      page = pfn_to_page(pfn);
      mapping = page_mapping(page);
      if (mapping) {
#ifndef CONFIG_SMP
            int dirty = test_and_clear_bit(PG_dcache_dirty, &page->flags);

            if (dirty)
                  __flush_dcache_page(mapping, page);
#endif

            if (cache_is_vivt())
                  make_coherent(mapping, vma, addr, pfn);
            else if (vma->vm_flags & VM_EXEC)
                  __flush_icache_all();
      }
}

/*
 * Check whether the write buffer has physical address aliasing
 * issues.  If it has, we need to avoid them for the case where
 * we have several shared mappings of the same object in user
 * space.
 */
static int __init check_writebuffer(unsigned long *p1, unsigned long *p2)
{
      register unsigned long zero = 0, one = 1, val;

      local_irq_disable();
      mb();
      *p1 = one;
      mb();
      *p2 = zero;
      mb();
      val = *p1;
      mb();
      local_irq_enable();
      return val != zero;
}

void __init check_writebuffer_bugs(void)
{
      struct page *page;
      const char *reason;
      unsigned long v = 1;

      printk(KERN_INFO "CPU: Testing write buffer coherency: ");

      page = alloc_page(GFP_KERNEL);
      if (page) {
            unsigned long *p1, *p2;
            pgprot_t prot = __pgprot(L_PTE_PRESENT|L_PTE_YOUNG|
                               L_PTE_DIRTY|L_PTE_WRITE|
                               L_PTE_BUFFERABLE);

            p1 = vmap(&page, 1, VM_IOREMAP, prot);
            p2 = vmap(&page, 1, VM_IOREMAP, prot);

            if (p1 && p2) {
                  v = check_writebuffer(p1, p2);
                  reason = "enabling work-around";
            } else {
                  reason = "unable to map memory\n";
            }

            vunmap(p1);
            vunmap(p2);
            put_page(page);
      } else {
            reason = "unable to grab page\n";
      }

      if (v) {
            printk("failed, %s\n", reason);
            shared_pte_mask |= L_PTE_BUFFERABLE;
      } else {
            printk("ok\n");
      }
}

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