[GitHub/exynos8895/android_kernel_samsung_universal8895.git] / arch / x86 / mm / gup.c

/*
 * Lockless get_user_pages_fast for x86
 *
 * Copyright (C) 2008 Nick Piggin
 * Copyright (C) 2008 Novell Inc.
 */
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/highmem.h>
#include <linux/swap.h>

#include <asm/pgtable.h>

static inline pte_t gup_get_pte(pte_t *ptep)
{
#ifndef CONFIG_X86_PAE
	return ACCESS_ONCE(*ptep);
#else
	/*
	 * With get_user_pages_fast, we walk down the pagetables without taking
	 * any locks.  For this we would like to load the pointers atomically,
	 * but that is not possible (without expensive cmpxchg8b) on PAE.  What
	 * we do have is the guarantee that a pte will only either go from not
	 * present to present, or present to not present or both -- it will not
	 * switch to a completely different present page without a TLB flush in
	 * between; something that we are blocking by holding interrupts off.
	 *
	 * Setting ptes from not present to present goes:
	 * ptep->pte_high = h;
	 * smp_wmb();
	 * ptep->pte_low = l;
	 *
	 * And present to not present goes:
	 * ptep->pte_low = 0;
	 * smp_wmb();
	 * ptep->pte_high = 0;
	 *
	 * We must ensure here that the load of pte_low sees l iff pte_high
	 * sees h. We load pte_high *after* loading pte_low, which ensures we
	 * don't see an older value of pte_high.  *Then* we recheck pte_low,
	 * which ensures that we haven't picked up a changed pte high. We might
	 * have got rubbish values from pte_low and pte_high, but we are
	 * guaranteed that pte_low will not have the present bit set *unless*
	 * it is 'l'. And get_user_pages_fast only operates on present ptes, so
	 * we're safe.
	 *
	 * gup_get_pte should not be used or copied outside gup.c without being
	 * very careful -- it does not atomically load the pte or anything that
	 * is likely to be useful for you.
	 */
	pte_t pte;

retry:
	pte.pte_low = ptep->pte_low;
	smp_rmb();
	pte.pte_high = ptep->pte_high;
	smp_rmb();
	if (unlikely(pte.pte_low != ptep->pte_low))
		goto retry;

	return pte;
#endif
}

/*
 * 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;
	pte_t *ptep;

	mask = _PAGE_PRESENT|_PAGE_USER;
	if (write)
		mask |= _PAGE_RW;

	ptep = pte_offset_map(&pmd, addr);
	do {
		pte_t pte = gup_get_pte(ptep);
		struct page *page;

		if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
			pte_unmap(ptep);
			return 0;
		}
		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
		page = pte_page(pte);
		get_page(page);
		SetPageReferenced(page);
		pages[*nr] = page;
		(*nr)++;

	} while (ptep++, addr += PAGE_SIZE, addr != end);
	pte_unmap(ptep - 1);

	return 1;
}

static inline void get_head_page_multiple(struct page *page, int nr)
{
	VM_BUG_ON(page != compound_head(page));
	VM_BUG_ON(page_count(page) == 0);
	atomic_add(nr, &page->_count);
	SetPageReferenced(page);
}

static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
		unsigned long end, int write, struct page **pages, int *nr)
{
	unsigned long mask;
	pte_t pte = *(pte_t *)&pmd;
	struct page *head, *page;
	int refs;

	mask = _PAGE_PRESENT|_PAGE_USER;
	if (write)
		mask |= _PAGE_RW;
	if ((pte_flags(pte) & mask) != mask)
		return 0;
	/* hugepages are never "special" */
	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

	refs = 0;
	head = pte_page(pte);
	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
	do {
		VM_BUG_ON(compound_head(page) != head);
		pages[*nr] = page;
		if (PageTail(page))
			get_huge_page_tail(page);
		(*nr)++;
		page++;
		refs++;
	} while (addr += PAGE_SIZE, addr != end);
	get_head_page_multiple(head, refs);

	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);
		/*
		 * The pmd_trans_splitting() check below explains why
		 * pmdp_splitting_flush has to flush the tlb, to stop
		 * this gup-fast code from running while we set the
		 * splitting bit in the pmd. Returning zero will take
		 * the slow path that will call wait_split_huge_page()
		 * if the pmd is still in splitting state. gup-fast
		 * can't because it has irq disabled and
		 * wait_split_huge_page() would never return as the
		 * tlb flush IPI wouldn't run.
		 */
		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
			return 0;
		if (unlikely(pmd_large(pmd))) {
			if (!gup_huge_pmd(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 noinline int gup_huge_pud(pud_t pud, unsigned long addr,
		unsigned long end, int write, struct page **pages, int *nr)
{
	unsigned long mask;
	pte_t pte = *(pte_t *)&pud;
	struct page *head, *page;
	int refs;

	mask = _PAGE_PRESENT|_PAGE_USER;
	if (write)
		mask |= _PAGE_RW;
	if ((pte_flags(pte) & mask) != mask)
		return 0;
	/* hugepages are never "special" */
	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

	refs = 0;
	head = pte_page(pte);
	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
	do {
		VM_BUG_ON(compound_head(page) != head);
		pages[*nr] = page;
		(*nr)++;
		page++;
		refs++;
	} while (addr += PAGE_SIZE, addr != end);
	get_head_page_multiple(head, refs);

	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 (unlikely(pud_large(pud))) {
			if (!gup_huge_pud(pud, addr, next, write, pages, nr))
				return 0;
		} else {
			if (!gup_pmd_range(pud, addr, next, write, pages, nr))
				return 0;
		}
	} while (pudp++, addr = next, addr != end);

	return 1;
}

/*
 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 * back to the regular GUP.
 */
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;
	unsigned long flags;
	pgd_t *pgdp;
	int nr = 0;

	start &= PAGE_MASK;
	addr = start;
	len = (unsigned long) nr_pages << PAGE_SHIFT;
	end = start + len;
	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
					(void __user *)start, len)))
		return 0;

	/*
	 * 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 and pages from being freed on x86.
	 *
	 * So long as we atomically load page table pointers versus teardown
	 * (which we do on x86, with the above PAE exception), we can follow the
	 * address down to the the page and take a ref on it.
	 */
	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;
}

/**
 * get_user_pages_fast() - pin user pages in memory
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
 * @write:	whether pages will be written to
 * @pages:	array that receives pointers to the pages pinned.
 * 		Should be at least nr_pages long.
 *
 * Attempt to pin user pages in memory without taking mm->mmap_sem.
 * If not successful, it will fall back to taking the lock and
 * calling get_user_pages().
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno.
 */
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;
	if (end < start)
		goto slow_irqon;

#ifdef CONFIG_X86_64
	if (end >> __VIRTUAL_MASK_SHIFT)
		goto slow_irqon;
#endif

	/*
	 * 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 and pages from being freed on x86.
	 *
	 * So long as we atomically load page table pointers versus teardown
	 * (which we do on x86, with the above PAE exception), 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();
slow_irqon:
		/* 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;
	}
}
Commit	Line	Data
8174c430 NP	1	/*
	2	* Lockless get_user_pages_fast for x86
	3	*
	4	* Copyright (C) 2008 Nick Piggin
	5	* Copyright (C) 2008 Novell Inc.
	6	*/
	7	#include <linux/sched.h>
	8	#include <linux/mm.h>
	9	#include <linux/vmstat.h>
	10	#include <linux/highmem.h>
8ee53820	11	#include <linux/swap.h>
8174c430 NP	12
	13	#include <asm/pgtable.h>
	14
	15	static inline pte_t gup_get_pte(pte_t *ptep)
	16	{
	17	#ifndef CONFIG_X86_PAE
0c871971	18	return ACCESS_ONCE(*ptep);
8174c430 NP	19	#else
	20	/*
	21	* With get_user_pages_fast, we walk down the pagetables without taking
ab09809f	22	* any locks. For this we would like to load the pointers atomically,
8174c430 NP	23	* but that is not possible (without expensive cmpxchg8b) on PAE. What
	24	* we do have is the guarantee that a pte will only either go from not
	25	* present to present, or present to not present or both -- it will not
	26	* switch to a completely different present page without a TLB flush in
	27	* between; something that we are blocking by holding interrupts off.
	28	*
	29	* Setting ptes from not present to present goes:
	30	* ptep->pte_high = h;
	31	* smp_wmb();
	32	* ptep->pte_low = l;
	33	*
	34	* And present to not present goes:
	35	* ptep->pte_low = 0;
	36	* smp_wmb();
	37	* ptep->pte_high = 0;
	38	*
	39	* We must ensure here that the load of pte_low sees l iff pte_high
	40	* sees h. We load pte_high after loading pte_low, which ensures we
	41	* don't see an older value of pte_high. Then we recheck pte_low,
	42	* which ensures that we haven't picked up a changed pte high. We might
	43	* have got rubbish values from pte_low and pte_high, but we are
	44	* guaranteed that pte_low will not have the present bit set unless
	45	* it is 'l'. And get_user_pages_fast only operates on present ptes, so
	46	* we're safe.
	47	*
	48	* gup_get_pte should not be used or copied outside gup.c without being
	49	* very careful -- it does not atomically load the pte or anything that
	50	* is likely to be useful for you.
	51	*/
	52	pte_t pte;
	53
	54	retry:
	55	pte.pte_low = ptep->pte_low;
	56	smp_rmb();
	57	pte.pte_high = ptep->pte_high;
	58	smp_rmb();
	59	if (unlikely(pte.pte_low != ptep->pte_low))
	60	goto retry;
	61
	62	return pte;
	63	#endif
	64	}
	65
	66	/*
	67	* The performance critical leaf functions are made noinline otherwise gcc
	68	* inlines everything into a single function which results in too much
	69	* register pressure.
	70	*/
	71	static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
	72	unsigned long end, int write, struct page *pages, int nr)
	73	{
	74	unsigned long mask;
	75	pte_t *ptep;
	76
	77	mask = _PAGE_PRESENT\|_PAGE_USER;
	78	if (write)
	79	mask \|= _PAGE_RW;
	80
	81	ptep = pte_offset_map(&pmd, addr);
	82	do {
	83	pte_t pte = gup_get_pte(ptep);
	84	struct page *page;
	85
606ee44d	86	if ((pte_flags(pte) & (mask \| _PAGE_SPECIAL)) != mask) {
8174c430 NP	87	pte_unmap(ptep);
	88	return 0;
	89	}
	90	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
	91	page = pte_page(pte);
	92	get_page(page);
8ee53820	93	SetPageReferenced(page);
8174c430 NP	94	pages[*nr] = page;
	95	(*nr)++;
	96
	97	} while (ptep++, addr += PAGE_SIZE, addr != end);
	98	pte_unmap(ptep - 1);
	99
	100	return 1;
	101	}
	102
	103	static inline void get_head_page_multiple(struct page *page, int nr)
	104	{
	105	VM_BUG_ON(page != compound_head(page));
	106	VM_BUG_ON(page_count(page) == 0);
	107	atomic_add(nr, &page->_count);
8ee53820	108	SetPageReferenced(page);
8174c430 NP	109	}
	110
	111	static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
	112	unsigned long end, int write, struct page *pages, int nr)
	113	{
	114	unsigned long mask;
	115	pte_t pte = (pte_t )&pmd;
	116	struct page head, page;
	117	int refs;
	118
	119	mask = _PAGE_PRESENT\|_PAGE_USER;
	120	if (write)
	121	mask \|= _PAGE_RW;
606ee44d	122	if ((pte_flags(pte) & mask) != mask)
8174c430 NP	123	return 0;
8174c430 NP	124	/* hugepages are never "special" */
606ee44d	125	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
8174c430 NP	126	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
	127
	128	refs = 0;
	129	head = pte_page(pte);
652ea695	130	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
8174c430 NP	131	do {
	132	VM_BUG_ON(compound_head(page) != head);
	133	pages[*nr] = page;
91807063 AA	134	if (PageTail(page))
91807063 AA	135	get_huge_page_tail(page);
8174c430 NP	136	(*nr)++;
	137	page++;
	138	refs++;
	139	} while (addr += PAGE_SIZE, addr != end);
	140	get_head_page_multiple(head, refs);
	141
	142	return 1;
	143	}
	144
	145	static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
	146	int write, struct page *pages, int nr)
	147	{
	148	unsigned long next;
	149	pmd_t *pmdp;
	150
	151	pmdp = pmd_offset(&pud, addr);
	152	do {
	153	pmd_t pmd = *pmdp;
	154
	155	next = pmd_addr_end(addr, end);
64cc6ae0 AA	156	/*
	157	* The pmd_trans_splitting() check below explains why
	158	* pmdp_splitting_flush has to flush the tlb, to stop
	159	* this gup-fast code from running while we set the
	160	* splitting bit in the pmd. Returning zero will take
	161	* the slow path that will call wait_split_huge_page()
	162	* if the pmd is still in splitting state. gup-fast
	163	* can't because it has irq disabled and
	164	* wait_split_huge_page() would never return as the
	165	* tlb flush IPI wouldn't run.
	166	*/
	167	if (pmd_none(pmd) \|\| pmd_trans_splitting(pmd))
8174c430 NP	168	return 0;
	169	if (unlikely(pmd_large(pmd))) {
	170	if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
	171	return 0;
	172	} else {
	173	if (!gup_pte_range(pmd, addr, next, write, pages, nr))
	174	return 0;
	175	}
	176	} while (pmdp++, addr = next, addr != end);
	177
	178	return 1;
	179	}
	180
652ea695 NP	181	static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
	182	unsigned long end, int write, struct page *pages, int nr)
	183	{
	184	unsigned long mask;
	185	pte_t pte = (pte_t )&pud;
	186	struct page head, page;
	187	int refs;
	188
	189	mask = _PAGE_PRESENT\|_PAGE_USER;
	190	if (write)
	191	mask \|= _PAGE_RW;
606ee44d	192	if ((pte_flags(pte) & mask) != mask)
652ea695 NP	193	return 0;
652ea695 NP	194	/* hugepages are never "special" */
606ee44d	195	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
652ea695 NP	196	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
	197
	198	refs = 0;
	199	head = pte_page(pte);
	200	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
	201	do {
	202	VM_BUG_ON(compound_head(page) != head);
	203	pages[*nr] = page;
	204	(*nr)++;
	205	page++;
	206	refs++;
	207	} while (addr += PAGE_SIZE, addr != end);
	208	get_head_page_multiple(head, refs);
	209
	210	return 1;
	211	}
	212
8174c430 NP	213	static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
	214	int write, struct page *pages, int nr)
	215	{
	216	unsigned long next;
	217	pud_t *pudp;
	218
	219	pudp = pud_offset(&pgd, addr);
	220	do {
	221	pud_t pud = *pudp;
	222
	223	next = pud_addr_end(addr, end);
	224	if (pud_none(pud))
	225	return 0;
652ea695 NP	226	if (unlikely(pud_large(pud))) {
	227	if (!gup_huge_pud(pud, addr, next, write, pages, nr))
	228	return 0;
	229	} else {
	230	if (!gup_pmd_range(pud, addr, next, write, pages, nr))
	231	return 0;
	232	}
8174c430 NP	233	} while (pudp++, addr = next, addr != end);
	234
	235	return 1;
	236	}
	237
465a454f PZ	238	/*
	239	* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
	240	* back to the regular GUP.
	241	*/
	242	int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
	243	struct page **pages)
	244	{
	245	struct mm_struct *mm = current->mm;
	246	unsigned long addr, len, end;
	247	unsigned long next;
	248	unsigned long flags;
	249	pgd_t *pgdp;
	250	int nr = 0;
	251
	252	start &= PAGE_MASK;
	253	addr = start;
	254	len = (unsigned long) nr_pages << PAGE_SHIFT;
	255	end = start + len;
	256	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
	257	(void __user *)start, len)))
	258	return 0;
	259
	260	/*
	261	* XXX: batch / limit 'nr', to avoid large irq off latency
	262	* needs some instrumenting to determine the common sizes used by
	263	* important workloads (eg. DB2), and whether limiting the batch size
	264	* will decrease performance.
	265	*
	266	* It seems like we're in the clear for the moment. Direct-IO is
	267	* the main guy that batches up lots of get_user_pages, and even
	268	* they are limited to 64-at-a-time which is not so many.
	269	*/
	270	/*
	271	* This doesn't prevent pagetable teardown, but does prevent
	272	* the pagetables and pages from being freed on x86.
	273	*
	274	* So long as we atomically load page table pointers versus teardown
	275	* (which we do on x86, with the above PAE exception), we can follow the
	276	* address down to the the page and take a ref on it.
	277	*/
	278	local_irq_save(flags);
	279	pgdp = pgd_offset(mm, addr);
	280	do {
	281	pgd_t pgd = *pgdp;
	282
	283	next = pgd_addr_end(addr, end);
	284	if (pgd_none(pgd))
	285	break;
	286	if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
	287	break;
	288	} while (pgdp++, addr = next, addr != end);
	289	local_irq_restore(flags);
	290
	291	return nr;
	292	}
	293
a0d22f48 AG	294	/**
	295	* get_user_pages_fast() - pin user pages in memory
	296	* @start: starting user address
	297	* @nr_pages: number of pages from start to pin
	298	* @write: whether pages will be written to
	299	* @pages: array that receives pointers to the pages pinned.
	300	* Should be at least nr_pages long.
	301	*
	302	* Attempt to pin user pages in memory without taking mm->mmap_sem.
	303	* If not successful, it will fall back to taking the lock and
	304	* calling get_user_pages().
	305	*
	306	* Returns number of pages pinned. This may be fewer than the number
	307	* requested. If nr_pages is 0 or negative, returns 0. If no pages
	308	* were pinned, returns -errno.
	309	*/
8174c430 NP	310	int get_user_pages_fast(unsigned long start, int nr_pages, int write,
	311	struct page **pages)
	312	{
	313	struct mm_struct *mm = current->mm;
9b79022c	314	unsigned long addr, len, end;
8174c430 NP	315	unsigned long next;
	316	pgd_t *pgdp;
	317	int nr = 0;
	318
9b79022c LT	319	start &= PAGE_MASK;
	320	addr = start;
	321	len = (unsigned long) nr_pages << PAGE_SHIFT;
7f818906	322
9b79022c	323	end = start + len;
7f818906 LT	324	if (end < start)
	325	goto slow_irqon;
	326
	327	#ifdef CONFIG_X86_64
	328	if (end >> __VIRTUAL_MASK_SHIFT)
8174c430	329	goto slow_irqon;
7f818906	330	#endif
8174c430 NP	331
	332	/*
	333	* XXX: batch / limit 'nr', to avoid large irq off latency
	334	* needs some instrumenting to determine the common sizes used by
	335	* important workloads (eg. DB2), and whether limiting the batch size
	336	* will decrease performance.
	337	*
	338	* It seems like we're in the clear for the moment. Direct-IO is
	339	* the main guy that batches up lots of get_user_pages, and even
	340	* they are limited to 64-at-a-time which is not so many.
	341	*/
	342	/*
	343	* This doesn't prevent pagetable teardown, but does prevent
	344	* the pagetables and pages from being freed on x86.
	345	*
	346	* So long as we atomically load page table pointers versus teardown
	347	* (which we do on x86, with the above PAE exception), we can follow the
	348	* address down to the the page and take a ref on it.
	349	*/
	350	local_irq_disable();
	351	pgdp = pgd_offset(mm, addr);
	352	do {
	353	pgd_t pgd = *pgdp;
	354
	355	next = pgd_addr_end(addr, end);
	356	if (pgd_none(pgd))
	357	goto slow;
	358	if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
	359	goto slow;
	360	} while (pgdp++, addr = next, addr != end);
	361	local_irq_enable();
	362
	363	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
	364	return nr;
	365
	366	{
	367	int ret;
	368
	369	slow:
	370	local_irq_enable();
	371	slow_irqon:
	372	/* Try to get the remaining pages with get_user_pages */
	373	start += nr << PAGE_SHIFT;
	374	pages += nr;
	375
	376	down_read(&mm->mmap_sem);
	377	ret = get_user_pages(current, mm, start,
	378	(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
	379	up_read(&mm->mmap_sem);
	380
	381	/* Have to be a bit careful with return values */
	382	if (nr > 0) {
	383	if (ret < 0)
	384	ret = nr;
	385	else
	386	ret += nr;
	387	}
	388
	389	return ret;
	390	}
	391	}