1/*
  2 *  Lockless get_user_pages_fast for s390
  3 *
  4 *  Copyright IBM Corp. 2010
  5 *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
  6 */
  7#include <linux/sched.h>
  8#include <linux/mm.h>
  9#include <linux/hugetlb.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 inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
 21		unsigned long end, int write, struct page **pages, int *nr)
 22{
 23	unsigned long mask;
 24	pte_t *ptep, pte;
 25	struct page *page;
 26
 27	mask = (write ? _PAGE_RO : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
 28
 29	ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
 30	do {
 31		pte = *ptep;
 32		barrier();
 33		if ((pte_val(pte) & mask) != 0)
 34			return 0;
 35		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 36		page = pte_page(pte);
 37		if (!page_cache_get_speculative(page))
 38			return 0;
 39		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
 40			put_page(page);
 41			return 0;
 42		}
 43		pages[*nr] = page;
 44		(*nr)++;
 45
 46	} while (ptep++, addr += PAGE_SIZE, addr != end);
 47
 48	return 1;
 49}
 50
 51static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
 52		unsigned long end, int write, struct page **pages, int *nr)
 53{
 54	unsigned long mask, result;
 55	struct page *head, *page;
 56	int refs;
 57
 58	result = write ? 0 : _SEGMENT_ENTRY_RO;
 59	mask = result | _SEGMENT_ENTRY_INV;
 60	if ((pmd_val(pmd) & mask) != result)
 61		return 0;
 62	VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
 63
 64	refs = 0;
 65	head = pmd_page(pmd);
 66	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 67	do {
 68		VM_BUG_ON(compound_head(page) != head);
 69		pages[*nr] = page;
 70		(*nr)++;
 71		page++;
 72		refs++;
 73	} while (addr += PAGE_SIZE, addr != end);
 74
 75	if (!page_cache_add_speculative(head, refs)) {
 76		*nr -= refs;
 77		return 0;
 78	}
 79
 80	if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
 81		*nr -= refs;
 82		while (refs--)
 83			put_page(head);
 84	}
 85
 86	return 1;
 87}
 88
 89
 90static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
 91		unsigned long end, int write, struct page **pages, int *nr)
 92{
 93	unsigned long next;
 94	pmd_t *pmdp, pmd;
 95
 96	pmdp = (pmd_t *) pudp;
 97#ifdef CONFIG_64BIT
 98	if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
 99		pmdp = (pmd_t *) pud_deref(pud);
100	pmdp += pmd_index(addr);
101#endif
102	do {
103		pmd = *pmdp;
104		barrier();
105		next = pmd_addr_end(addr, end);
106		if (pmd_none(pmd))
107			return 0;
108		if (unlikely(pmd_huge(pmd))) {
109			if (!gup_huge_pmd(pmdp, pmd, addr, next,
110					  write, pages, nr))
111				return 0;
112		} else if (!gup_pte_range(pmdp, pmd, addr, next,
113					  write, pages, nr))
114			return 0;
115	} while (pmdp++, addr = next, addr != end);
116
117	return 1;
118}
119
120static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
121		unsigned long end, int write, struct page **pages, int *nr)
122{
123	unsigned long next;
124	pud_t *pudp, pud;
125
126	pudp = (pud_t *) pgdp;
127#ifdef CONFIG_64BIT
128	if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
129		pudp = (pud_t *) pgd_deref(pgd);
130	pudp += pud_index(addr);
131#endif
132	do {
133		pud = *pudp;
134		barrier();
135		next = pud_addr_end(addr, end);
136		if (pud_none(pud))
137			return 0;
138		if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
139			return 0;
140	} while (pudp++, addr = next, addr != end);
141
142	return 1;
143}
144
145/**
146 * get_user_pages_fast() - pin user pages in memory
147 * @start:	starting user address
148 * @nr_pages:	number of pages from start to pin
149 * @write:	whether pages will be written to
150 * @pages:	array that receives pointers to the pages pinned.
151 *		Should be at least nr_pages long.
152 *
153 * Attempt to pin user pages in memory without taking mm->mmap_sem.
154 * If not successful, it will fall back to taking the lock and
155 * calling get_user_pages().
156 *
157 * Returns number of pages pinned. This may be fewer than the number
158 * requested. If nr_pages is 0 or negative, returns 0. If no pages
159 * were pinned, returns -errno.
160 */
161int get_user_pages_fast(unsigned long start, int nr_pages, int write,
162			struct page **pages)
163{
164	struct mm_struct *mm = current->mm;
165	unsigned long addr, len, end;
166	unsigned long next;
167	pgd_t *pgdp, pgd;
168	int nr = 0;
169
170	start &= PAGE_MASK;
171	addr = start;
172	len = (unsigned long) nr_pages << PAGE_SHIFT;
173	end = start + len;
174	if (end < start)
175		goto slow_irqon;
176
177	/*
178	 * local_irq_disable() doesn't prevent pagetable teardown, but does
179	 * prevent the pagetables from being freed on s390.
180	 *
181	 * So long as we atomically load page table pointers versus teardown,
182	 * we can follow the address down to the the page and take a ref on it.
183	 */
184	local_irq_disable();
185	pgdp = pgd_offset(mm, addr);
186	do {
187		pgd = *pgdp;
188		barrier();
189		next = pgd_addr_end(addr, end);
190		if (pgd_none(pgd))
191			goto slow;
192		if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
193			goto slow;
194	} while (pgdp++, addr = next, addr != end);
195	local_irq_enable();
196
197	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
198	return nr;
199
200	{
201		int ret;
202slow:
203		local_irq_enable();
204slow_irqon:
205		/* Try to get the remaining pages with get_user_pages */
206		start += nr << PAGE_SHIFT;
207		pages += nr;
208
209		down_read(&mm->mmap_sem);
210		ret = get_user_pages(current, mm, start,
211			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
212		up_read(&mm->mmap_sem);
213
214		/* Have to be a bit careful with return values */
215		if (nr > 0) {
216			if (ret < 0)
217				ret = nr;
218			else
219				ret += nr;
220		}
221
222		return ret;
223	}
224}