1/*
  2 * Lockless get_user_pages_fast for sparc, cribbed from powerpc
  3 *
  4 * Copyright (C) 2008 Nick Piggin
  5 * Copyright (C) 2008 Novell Inc.
  6 */
  7
  8#include <linux/sched.h>
  9#include <linux/mm.h>
 10#include <linux/vmstat.h>
 11#include <linux/pagemap.h>
 12#include <linux/rwsem.h>
 13#include <asm/pgtable.h>
 14
 15/*
 16 * The performance critical leaf functions are made noinline otherwise gcc
 17 * inlines everything into a single function which results in too much
 18 * register pressure.
 19 */
 20static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 21		unsigned long end, int write, struct page **pages, int *nr)
 22{
 23	unsigned long mask, result;
 24	pte_t *ptep;
 25
 26	if (tlb_type == hypervisor) {
 27		result = _PAGE_PRESENT_4V|_PAGE_P_4V;
 28		if (write)
 29			result |= _PAGE_WRITE_4V;
 30	} else {
 31		result = _PAGE_PRESENT_4U|_PAGE_P_4U;
 32		if (write)
 33			result |= _PAGE_WRITE_4U;
 34	}
 35	mask = result | _PAGE_SPECIAL;
 36
 37	ptep = pte_offset_kernel(&pmd, addr);
 38	do {
 39		struct page *page, *head;
 40		pte_t pte = *ptep;
 41
 42		if ((pte_val(pte) & mask) != result)
 43			return 0;
 44		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 45
 46		/* The hugepage case is simplified on sparc64 because
 47		 * we encode the sub-page pfn offsets into the
 48		 * hugepage PTEs.  We could optimize this in the future
 49		 * use page_cache_add_speculative() for the hugepage case.
 50		 */
 51		page = pte_page(pte);
 52		head = compound_head(page);
 53		if (!page_cache_get_speculative(head))
 54			return 0;
 55		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
 56			put_page(head);
 57			return 0;
 58		}
 59
 60		pages[*nr] = page;
 61		(*nr)++;
 62	} while (ptep++, addr += PAGE_SIZE, addr != end);
 63
 64	return 1;
 65}
 66
 67static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 68		int write, struct page **pages, int *nr)
 69{
 70	unsigned long next;
 71	pmd_t *pmdp;
 72
 73	pmdp = pmd_offset(&pud, addr);
 74	do {
 75		pmd_t pmd = *pmdp;
 76
 77		next = pmd_addr_end(addr, end);
 78		if (pmd_none(pmd))
 79			return 0;
 80		if (!gup_pte_range(pmd, addr, next, write, pages, nr))
 81			return 0;
 82	} while (pmdp++, addr = next, addr != end);
 83
 84	return 1;
 85}
 86
 87static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 88		int write, struct page **pages, int *nr)
 89{
 90	unsigned long next;
 91	pud_t *pudp;
 92
 93	pudp = pud_offset(&pgd, addr);
 94	do {
 95		pud_t pud = *pudp;
 96
 97		next = pud_addr_end(addr, end);
 98		if (pud_none(pud))
 99			return 0;
100		if (!gup_pmd_range(pud, addr, next, write, pages, nr))
101			return 0;
102	} while (pudp++, addr = next, addr != end);
103
104	return 1;
105}
106
107int get_user_pages_fast(unsigned long start, int nr_pages, int write,
108			struct page **pages)
109{
110	struct mm_struct *mm = current->mm;
111	unsigned long addr, len, end;
112	unsigned long next;
113	pgd_t *pgdp;
114	int nr = 0;
115
116	start &= PAGE_MASK;
117	addr = start;
118	len = (unsigned long) nr_pages << PAGE_SHIFT;
119	end = start + len;
120
121	/*
122	 * XXX: batch / limit 'nr', to avoid large irq off latency
123	 * needs some instrumenting to determine the common sizes used by
124	 * important workloads (eg. DB2), and whether limiting the batch size
125	 * will decrease performance.
126	 *
127	 * It seems like we're in the clear for the moment. Direct-IO is
128	 * the main guy that batches up lots of get_user_pages, and even
129	 * they are limited to 64-at-a-time which is not so many.
130	 */
131	/*
132	 * This doesn't prevent pagetable teardown, but does prevent
133	 * the pagetables from being freed on sparc.
134	 *
135	 * So long as we atomically load page table pointers versus teardown,
136	 * we can follow the address down to the the page and take a ref on it.
137	 */
138	local_irq_disable();
139
140	pgdp = pgd_offset(mm, addr);
141	do {
142		pgd_t pgd = *pgdp;
143
144		next = pgd_addr_end(addr, end);
145		if (pgd_none(pgd))
146			goto slow;
147		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
148			goto slow;
149	} while (pgdp++, addr = next, addr != end);
150
151	local_irq_enable();
152
153	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
154	return nr;
155
156	{
157		int ret;
158
159slow:
160		local_irq_enable();
161
162		/* Try to get the remaining pages with get_user_pages */
163		start += nr << PAGE_SHIFT;
164		pages += nr;
165
166		down_read(&mm->mmap_sem);
167		ret = get_user_pages(current, mm, start,
168			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
169		up_read(&mm->mmap_sem);
170
171		/* Have to be a bit careful with return values */
172		if (nr > 0) {
173			if (ret < 0)
174				ret = nr;
175			else
176				ret += nr;
177		}
178
179		return ret;
180	}
181}