arch/mips/mm/gup.c - third_party/linux - Git at Google

 /*
  * 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/cpu-features.h>
 #include <asm/pgtable.h>

 static inline pte_t gup_get_pte(pte_t *ptep)
 {
 #if defined(CONFIG_PHYS_ADDR_T_64BIT) && 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 READ_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);
 	page_ref_add(page, nr);
 	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;
 		(*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);
 		if (pmd_none(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 || cpu_has_dc_aliases)
 		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;
 		/*
 		 * The FAST_GUP case requires FOLL_WRITE even for pure reads,
 		 * because get_user_pages() may need to cause an early COW in
 		 * order to avoid confusing the normal COW routines. So only
 		 * targets that are already writable are safe to do by just
 		 * looking at the page tables.
 		 */
 		if (!gup_pud_range(pgd, addr, next, 1, 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;

 	ret = get_user_pages_unlocked(start, (end - start) >> PAGE_SHIFT,
 				      pages, write ? FOLL_WRITE : 0);

 	/* Have to be a bit careful with return values */
 	if (nr > 0) {
 		if (ret < 0)
 			ret = nr;
 		else
 			ret += nr;
 	}
 	return ret;
 }
	/*
	* 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/cpu-features.h>
	#include <asm/pgtable.h>

	static inline pte_t gup_get_pte(pte_t *ptep)
	{
	#if defined(CONFIG_PHYS_ADDR_T_64BIT) && 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 READ_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);
	page_ref_add(page, nr);
	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;
	(*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);
	if (pmd_none(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 \|\| cpu_has_dc_aliases)
	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;
	/*
	* The FAST_GUP case requires FOLL_WRITE even for pure reads,
	* because get_user_pages() may need to cause an early COW in
	* order to avoid confusing the normal COW routines. So only
	* targets that are already writable are safe to do by just
	* looking at the page tables.
	*/
	if (!gup_pud_range(pgd, addr, next, 1, 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;

	ret = get_user_pages_unlocked(start, (end - start) >> PAGE_SHIFT,
	pages, write ? FOLL_WRITE : 0);

	/* Have to be a bit careful with return values */
	if (nr > 0) {
	if (ret < 0)
	ret = nr;
	else
	ret += nr;
	}
	return ret;
	}