1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Lockless get_user_pages_fast for SuperH
  4 *
  5 * Copyright (C) 2009 - 2010  Paul Mundt
  6 *
  7 * Cloned from the x86 and PowerPC versions, by:
  8 *
  9 *	Copyright (C) 2008 Nick Piggin
 10 *	Copyright (C) 2008 Novell Inc.
 11 */
 12#include <linux/sched.h>
 13#include <linux/mm.h>
 14#include <linux/vmstat.h>
 15#include <linux/highmem.h>
 16#include <asm/pgtable.h>
 17
 18static inline pte_t gup_get_pte(pte_t *ptep)
 19{
 20#ifndef CONFIG_X2TLB
 21	return READ_ONCE(*ptep);
 22#else
 23	/*
 24	 * With get_user_pages_fast, we walk down the pagetables without
 25	 * taking any locks.  For this we would like to load the pointers
 26	 * atomically, but that is not possible with 64-bit PTEs.  What
 27	 * we do have is the guarantee that a pte will only either go
 28	 * from not present to present, or present to not present or both
 29	 * -- it will not switch to a completely different present page
 30	 * without a TLB flush in between; something that we are blocking
 31	 * by holding interrupts off.
 32	 *
 33	 * Setting ptes from not present to present goes:
 34	 * ptep->pte_high = h;
 35	 * smp_wmb();
 36	 * ptep->pte_low = l;
 37	 *
 38	 * And present to not present goes:
 39	 * ptep->pte_low = 0;
 40	 * smp_wmb();
 41	 * ptep->pte_high = 0;
 42	 *
 43	 * We must ensure here that the load of pte_low sees l iff pte_high
 44	 * sees h. We load pte_high *after* loading pte_low, which ensures we
 45	 * don't see an older value of pte_high.  *Then* we recheck pte_low,
 46	 * which ensures that we haven't picked up a changed pte high. We might
 47	 * have got rubbish values from pte_low and pte_high, but we are
 48	 * guaranteed that pte_low will not have the present bit set *unless*
 49	 * it is 'l'. And get_user_pages_fast only operates on present ptes, so
 50	 * we're safe.
 51	 *
 52	 * gup_get_pte should not be used or copied outside gup.c without being
 53	 * very careful -- it does not atomically load the pte or anything that
 54	 * is likely to be useful for you.
 55	 */
 56	pte_t pte;
 57
 58retry:
 59	pte.pte_low = ptep->pte_low;
 60	smp_rmb();
 61	pte.pte_high = ptep->pte_high;
 62	smp_rmb();
 63	if (unlikely(pte.pte_low != ptep->pte_low))
 64		goto retry;
 65
 66	return pte;
 67#endif
 68}
 69
 70/*
 71 * The performance critical leaf functions are made noinline otherwise gcc
 72 * inlines everything into a single function which results in too much
 73 * register pressure.
 74 */
 75static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 76		unsigned long end, int write, struct page **pages, int *nr)
 77{
 78	u64 mask, result;
 79	pte_t *ptep;
 80
 81#ifdef CONFIG_X2TLB
 82	result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
 83	if (write)
 84		result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
 85#elif defined(CONFIG_SUPERH64)
 86	result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
 87	if (write)
 88		result |= _PAGE_WRITE;
 89#else
 90	result = _PAGE_PRESENT | _PAGE_USER;
 91	if (write)
 92		result |= _PAGE_RW;
 93#endif
 94
 95	mask = result | _PAGE_SPECIAL;
 96
 97	ptep = pte_offset_map(&pmd, addr);
 98	do {
 99		pte_t pte = gup_get_pte(ptep);
100		struct page *page;
101
102		if ((pte_val(pte) & mask) != result) {
103			pte_unmap(ptep);
104			return 0;
105		}
106		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
107		page = pte_page(pte);
108		get_page(page);
109		__flush_anon_page(page, addr);
110		flush_dcache_page(page);
111		pages[*nr] = page;
112		(*nr)++;
113
114	} while (ptep++, addr += PAGE_SIZE, addr != end);
115	pte_unmap(ptep - 1);
116
117	return 1;
118}
119
120static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
121		int write, struct page **pages, int *nr)
122{
123	unsigned long next;
124	pmd_t *pmdp;
125
126	pmdp = pmd_offset(&pud, addr);
127	do {
128		pmd_t pmd = *pmdp;
129
130		next = pmd_addr_end(addr, end);
131		if (pmd_none(pmd))
132			return 0;
133		if (!gup_pte_range(pmd, addr, next, write, pages, nr))
134			return 0;
135	} while (pmdp++, addr = next, addr != end);
136
137	return 1;
138}
139
140static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
141			int write, struct page **pages, int *nr)
142{
143	unsigned long next;
144	pud_t *pudp;
145
146	pudp = pud_offset(&pgd, addr);
147	do {
148		pud_t pud = *pudp;
149
150		next = pud_addr_end(addr, end);
151		if (pud_none(pud))
152			return 0;
153		if (!gup_pmd_range(pud, addr, next, write, pages, nr))
154			return 0;
155	} while (pudp++, addr = next, addr != end);
156
157	return 1;
158}
159
160/*
161 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
162 * back to the regular GUP.
163 * Note a difference with get_user_pages_fast: this always returns the
164 * number of pages pinned, 0 if no pages were pinned.
165 */
166int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
167			  struct page **pages)
168{
169	struct mm_struct *mm = current->mm;
170	unsigned long addr, len, end;
171	unsigned long next;
172	unsigned long flags;
173	pgd_t *pgdp;
174	int nr = 0;
175
176	start &= PAGE_MASK;
177	addr = start;
178	len = (unsigned long) nr_pages << PAGE_SHIFT;
179	end = start + len;
180	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
181					(void __user *)start, len)))
182		return 0;
183
184	/*
185	 * This doesn't prevent pagetable teardown, but does prevent
186	 * the pagetables and pages from being freed.
187	 */
188	local_irq_save(flags);
189	pgdp = pgd_offset(mm, addr);
190	do {
191		pgd_t pgd = *pgdp;
192
193		next = pgd_addr_end(addr, end);
194		if (pgd_none(pgd))
195			break;
196		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
197			break;
198	} while (pgdp++, addr = next, addr != end);
199	local_irq_restore(flags);
200
201	return nr;
202}
203
204/**
205 * get_user_pages_fast() - pin user pages in memory
206 * @start:	starting user address
207 * @nr_pages:	number of pages from start to pin
208 * @write:	whether pages will be written to
209 * @pages:	array that receives pointers to the pages pinned.
210 *		Should be at least nr_pages long.
211 *
212 * Attempt to pin user pages in memory without taking mm->mmap_sem.
213 * If not successful, it will fall back to taking the lock and
214 * calling get_user_pages().
215 *
216 * Returns number of pages pinned. This may be fewer than the number
217 * requested. If nr_pages is 0 or negative, returns 0. If no pages
218 * were pinned, returns -errno.
219 */
220int get_user_pages_fast(unsigned long start, int nr_pages, int write,
221			struct page **pages)
222{
223	struct mm_struct *mm = current->mm;
224	unsigned long addr, len, end;
225	unsigned long next;
226	pgd_t *pgdp;
227	int nr = 0;
228
229	start &= PAGE_MASK;
230	addr = start;
231	len = (unsigned long) nr_pages << PAGE_SHIFT;
232
233	end = start + len;
234	if (end < start)
235		goto slow_irqon;
236
237	local_irq_disable();
238	pgdp = pgd_offset(mm, addr);
239	do {
240		pgd_t pgd = *pgdp;
241
242		next = pgd_addr_end(addr, end);
243		if (pgd_none(pgd))
244			goto slow;
245		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
246			goto slow;
247	} while (pgdp++, addr = next, addr != end);
248	local_irq_enable();
249
250	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
251	return nr;
252
253	{
254		int ret;
255
256slow:
257		local_irq_enable();
258slow_irqon:
259		/* Try to get the remaining pages with get_user_pages */
260		start += nr << PAGE_SHIFT;
261		pages += nr;
262
263		ret = get_user_pages_unlocked(start,
264			(end - start) >> PAGE_SHIFT, pages,
265			write ? FOLL_WRITE : 0);
266
267		/* Have to be a bit careful with return values */
268		if (nr > 0) {
269			if (ret < 0)
270				ret = nr;
271			else
272				ret += nr;
273		}
274
275		return ret;
276	}
277}