/*
   * Lockless get_user_pages_fast for sparc, cribbed from powerpc
   *
   * Copyright (C) 2008 Nick Piggin
   * Copyright (C) 2008 Novell Inc.
   */
  
  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <linux/vmstat.h>
  #include <linux/pagemap.h>
  #include <linux/rwsem.h>
  #include <asm/pgtable.h>
  
  /*
   * The performance critical leaf functions are made noinline otherwise gcc
   * inlines everything into a single function which results in too much
   * register pressure.
   */
  static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
  		unsigned long end, int write, struct page **pages, int *nr)
  {
  	unsigned long mask, result;
  	pte_t *ptep;
  
  	if (tlb_type == hypervisor) {
  		result = _PAGE_PRESENT_4V|_PAGE_P_4V;
  		if (write)
  			result |= _PAGE_WRITE_4V;
  	} else {
  		result = _PAGE_PRESENT_4U|_PAGE_P_4U;
  		if (write)
  			result |= _PAGE_WRITE_4U;
  	}
  	mask = result | _PAGE_SPECIAL;
  
  	ptep = pte_offset_kernel(&pmd, addr);
  	do {
  		struct page *page, *head;
  		pte_t pte = *ptep;
  
  		if ((pte_val(pte) & mask) != result)
  			return 0;
  		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  
  		/* The hugepage case is simplified on sparc64 because
  		 * we encode the sub-page pfn offsets into the
  		 * hugepage PTEs.  We could optimize this in the future
  		 * use page_cache_add_speculative() for the hugepage case.
  		 */
  		page = pte_page(pte);
  		head = compound_head(page);
  		if (!page_cache_get_speculative(head))
  			return 0;
  		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  			put_page(head);
  			return 0;
  		}
  		if (head != page)
  			get_huge_page_tail(page);
  
  		pages[*nr] = page;
  		(*nr)++;
  	} while (ptep++, addr += PAGE_SIZE, addr != end);
  
  	return 1;
  }
  
  static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  			unsigned long end, int write, struct page **pages,
  			int *nr)
  {
  	struct page *head, *page, *tail;
  	int refs;
  
  	if (!(pmd_val(pmd) & _PAGE_VALID))
  		return 0;
  
  	if (write && !pmd_write(pmd))
  		return 0;
  
  	refs = 0;
  	head = pmd_page(pmd);
  	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  	tail = page;
  	do {
  		VM_BUG_ON(compound_head(page) != head);
  		pages[*nr] = page;
  		(*nr)++;
  		page++;
  		refs++;
  	} while (addr += PAGE_SIZE, addr != end);
  
  	if (!page_cache_add_speculative(head, refs)) {
  		*nr -= refs;
  		return 0;
  	}
  
  	if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  		*nr -= refs;
  		while (refs--)
  			put_page(head);
  		return 0;
  	}
  
  	/* Any tail page need their mapcount reference taken before we
  	 * return.
  	 */
  	while (refs--) {
  		if (PageTail(tail))
  			get_huge_page_tail(tail);
  		tail++;
  	}
  
  	return 1;
  }
  
  static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
  		int write, struct page **pages, int *nr)
  {
  	unsigned long next;
  	pmd_t *pmdp;
  
  	pmdp = pmd_offset(&pud, addr);
  	do {
  		pmd_t pmd = *pmdp;
  
  		next = pmd_addr_end(addr, end);
  		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
  			return 0;
  		if (unlikely(pmd_large(pmd))) {
  			if (!gup_huge_pmd(pmdp, pmd, addr, next,
  					  write, pages, nr))
  				return 0;
  		} else if (!gup_pte_range(pmd, addr, next, write,
  					  pages, nr))
  			return 0;
  	} while (pmdp++, addr = next, addr != end);
  
  	return 1;
  }
  
  static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
  		int write, struct page **pages, int *nr)
  {
  	unsigned long next;
  	pud_t *pudp;
  
  	pudp = pud_offset(&pgd, addr);
  	do {
  		pud_t pud = *pudp;
  
  		next = pud_addr_end(addr, end);
  		if (pud_none(pud))
  			return 0;
  		if (!gup_pmd_range(pud, addr, next, write, pages, nr))
  			return 0;
  	} while (pudp++, addr = next, addr != end);
  
  	return 1;
  }
  
  int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
  			  struct page **pages)
  {
  	struct mm_struct *mm = current->mm;
  	unsigned long addr, len, end;
  	unsigned long next, flags;
  	pgd_t *pgdp;
  	int nr = 0;
  
  	start &= PAGE_MASK;
  	addr = start;
  	len = (unsigned long) nr_pages << PAGE_SHIFT;
  	end = start + len;
  
  	local_irq_save(flags);
  	pgdp = pgd_offset(mm, addr);
  	do {
  		pgd_t pgd = *pgdp;
  
  		next = pgd_addr_end(addr, end);
  		if (pgd_none(pgd))
  			break;
  		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
  			break;
  	} while (pgdp++, addr = next, addr != end);
  	local_irq_restore(flags);
  
  	return nr;
  }
  
  int get_user_pages_fast(unsigned long start, int nr_pages, int write,
  			struct page **pages)
  {
  	struct mm_struct *mm = current->mm;
  	unsigned long addr, len, end;
  	unsigned long next;
  	pgd_t *pgdp;
  	int nr = 0;
  
  	start &= PAGE_MASK;
  	addr = start;
  	len = (unsigned long) nr_pages << PAGE_SHIFT;
  	end = start + len;
  
  	/*
  	 * XXX: batch / limit 'nr', to avoid large irq off latency
  	 * needs some instrumenting to determine the common sizes used by
  	 * important workloads (eg. DB2), and whether limiting the batch size
  	 * will decrease performance.
  	 *
  	 * It seems like we're in the clear for the moment. Direct-IO is
  	 * the main guy that batches up lots of get_user_pages, and even
  	 * they are limited to 64-at-a-time which is not so many.
  	 */
  	/*
  	 * This doesn't prevent pagetable teardown, but does prevent
  	 * the pagetables from being freed on sparc.
  	 *
  	 * So long as we atomically load page table pointers versus teardown,
  	 * we can follow the address down to the the page and take a ref on it.
  	 */
  	local_irq_disable();
  
  	pgdp = pgd_offset(mm, addr);
  	do {
  		pgd_t pgd = *pgdp;
  
  		next = pgd_addr_end(addr, end);
  		if (pgd_none(pgd))
  			goto slow;
  		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
  			goto slow;
  	} while (pgdp++, addr = next, addr != end);
  
  	local_irq_enable();
  
  	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
  	return nr;
  
  	{
  		int ret;
  
  slow:
  		local_irq_enable();
  
  		/* Try to get the remaining pages with get_user_pages */
  		start += nr << PAGE_SHIFT;
  		pages += nr;
  
  		down_read(&mm->mmap_sem);
  		ret = get_user_pages(current, mm, start,
  			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
  		up_read(&mm->mmap_sem);
  
  		/* Have to be a bit careful with return values */
  		if (nr > 0) {
  			if (ret < 0)
  				ret = nr;
  			else
  				ret += nr;
  		}
  
  		return ret;
  	}
  }