MIPS: Add fast get_user_pages

#

obj-y				+= cache.o dma-default.o extable.o fault.o \

				   init.o mmap.o tlbex.o tlbex-fault.o uasm.o \

				   page.o

				   gup.o init.o mmap.o page.o tlbex.o \

				   tlbex-fault.o uasm.o

obj-$(CONFIG_32BIT)		+= ioremap.o pgtable-32.o

obj-$(CONFIG_64BIT)		+= pgtable-64.o

/*

 * Lockless get_user_pages_fast for MIPS

 *

 * Copyright (C) 2008 Nick Piggin

 * Copyright (C) 2008 Novell Inc.

 * Copyright (C) 2011 Ralf Baechle

 */

#include <linux/sched.h>

#include <linux/mm.h>

#include <linux/vmstat.h>

#include <linux/highmem.h>

#include <linux/swap.h>

#include <linux/hugetlb.h>

#include <asm/pgtable.h>

static inline pte_t gup_get_pte(pte_t *ptep)

{

#if defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32)

	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;

#else

	return ACCESS_ONCE(*ptep);

#endif

}

static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

			int write, struct page **pages, int *nr)

{

	pte_t *ptep = pte_offset_map(&pmd, addr);

	do {

		pte_t pte = gup_get_pte(ptep);

		struct page *page;

		if (!pte_present(pte) ||

		    pte_special(pte) || (write && !pte_write(pte))) {

			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 int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,

			int write, struct page **pages, int *nr)

{

	pte_t pte = *(pte_t *)&pmd;

	struct page *head, *page;

	int refs;

	if (write && !pte_write(pte))

		return 0;

	/* hugepages are never "special" */

	VM_BUG_ON(pte_special(pte));

	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_huge(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 int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,

			int write, struct page **pages, int *nr)

{

	pte_t pte = *(pte_t *)&pud;

	struct page *head, *page;

	int refs;

	if (write && !pte_write(pte))

		return 0;

	/* hugepages are never "special" */

	VM_BUG_ON(pte_special(pte));

	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_huge(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.

	 *

	 * So long as we atomically load page table pointers versus teardown,

	 * we can follow the address down to 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 ret, nr = 0;

	start &= PAGE_MASK;

	addr = start;

	len = (unsigned long) nr_pages << PAGE_SHIFT;

	end = start + len;

	if (end < start)

		goto slow_irqon;

	/* XXX: batch / limit 'nr' */

	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;

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;

}