sh: lockless get_user_pages_fast()

obj-y			+= $(cacheops-y)

mmu-y			:= nommu.o extable_32.o

mmu-$(CONFIG_MMU)	:= extable_$(BITS).o fault_$(BITS).o \

mmu-$(CONFIG_MMU)	:= extable_$(BITS).o fault_$(BITS).o gup.o \

			   ioremap.o kmap.o pgtable.o tlbflush_$(BITS).o

obj-y			+= $(mmu-y)

/*

 * Lockless get_user_pages_fast for SuperH

 *

 * Copyright (C) 2009 - 2010  Paul Mundt

 *

 * Cloned from the x86 and PowerPC versions, by:

 *

 *	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 <asm/pgtable.h>

static inline pte_t gup_get_pte(pte_t *ptep)

{

#ifndef CONFIG_X2TLB

	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 with 64-bit PTEs.  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)

{

	u64 mask, result;

	pte_t *ptep;

#ifdef CONFIG_X2TLB

	result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);

	if (write)

		result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);

#elif defined(CONFIG_SUPERH64)

	result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;

	if (write)

		result |= _PAGE_WRITE;

#else

	result = _PAGE_PRESENT | _PAGE_USER;

	if (write)

		result |= _PAGE_RW;

#endif

	mask = result | _PAGE_SPECIAL;

	ptep = pte_offset_map(&pmd, addr);

	do {

		pte_t pte = gup_get_pte(ptep);

		struct page *page;

		if ((pte_val(pte) & mask) != result) {

			pte_unmap(ptep);

			return 0;

		}

		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

		page = pte_page(pte);

		get_page(page);

		pages[*nr] = page;

		(*nr)++;

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

	pte_unmap(ptep - 1);

	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 (!gup_pte_range(pmd, addr, next, write, pages, nr))

			return 0;

	} while (pmdp++, addr = next, addr != end);

	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 (!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;

	/*

	 * This doesn't prevent pagetable teardown, but does prevent

	 * the pagetables and pages from being freed.

	 */

	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;

	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;

	}

}