Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 2165 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
new file mode 100644
index 000000000000..fb6e5deb873a
--- /dev/null
+++ b/mm/memory.c
@@ -0,0 +1,2165 @@
+/*
+ *  linux/mm/memory.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ */
+
+/*
+ * demand-loading started 01.12.91 - seems it is high on the list of
+ * things wanted, and it should be easy to implement. - Linus
+ */
+
+/*
+ * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
+ * pages started 02.12.91, seems to work. - Linus.
+ *
+ * Tested sharing by executing about 30 /bin/sh: under the old kernel it
+ * would have taken more than the 6M I have free, but it worked well as
+ * far as I could see.
+ *
+ * Also corrected some "invalidate()"s - I wasn't doing enough of them.
+ */
+
+/*
+ * Real VM (paging to/from disk) started 18.12.91. Much more work and
+ * thought has to go into this. Oh, well..
+ * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
+ *		Found it. Everything seems to work now.
+ * 20.12.91  -  Ok, making the swap-device changeable like the root.
+ */
+
+/*
+ * 05.04.94  -  Multi-page memory management added for v1.1.
+ * 		Idea by Alex Bligh (alex@cconcepts.co.uk)
+ *
+ * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
+ *		(Gerhard.Wichert@pdb.siemens.de)
+ *
+ * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
+ */
+
+#include <linux/kernel_stat.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/module.h>
+#include <linux/init.h>
+
+#include <asm/pgalloc.h>
+#include <asm/uaccess.h>
+#include <asm/tlb.h>
+#include <asm/tlbflush.h>
+#include <asm/pgtable.h>
+
+#include <linux/swapops.h>
+#include <linux/elf.h>
+
+#ifndef CONFIG_DISCONTIGMEM
+/* use the per-pgdat data instead for discontigmem - mbligh */
+unsigned long max_mapnr;
+struct page *mem_map;
+
+EXPORT_SYMBOL(max_mapnr);
+EXPORT_SYMBOL(mem_map);
+#endif
+
+unsigned long num_physpages;
+/*
+ * A number of key systems in x86 including ioremap() rely on the assumption
+ * that high_memory defines the upper bound on direct map memory, then end
+ * of ZONE_NORMAL.  Under CONFIG_DISCONTIG this means that max_low_pfn and
+ * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL
+ * and ZONE_HIGHMEM.
+ */
+void * high_memory;
+unsigned long vmalloc_earlyreserve;
+
+EXPORT_SYMBOL(num_physpages);
+EXPORT_SYMBOL(high_memory);
+EXPORT_SYMBOL(vmalloc_earlyreserve);
+
+/*
+ * If a p?d_bad entry is found while walking page tables, report
+ * the error, before resetting entry to p?d_none.  Usually (but
+ * very seldom) called out from the p?d_none_or_clear_bad macros.
+ */
+
+void pgd_clear_bad(pgd_t *pgd)
+{
+	pgd_ERROR(*pgd);
+	pgd_clear(pgd);
+}
+
+void pud_clear_bad(pud_t *pud)
+{
+	pud_ERROR(*pud);
+	pud_clear(pud);
+}
+
+void pmd_clear_bad(pmd_t *pmd)
+{
+	pmd_ERROR(*pmd);
+	pmd_clear(pmd);
+}
+
+/*
+ * Note: this doesn't free the actual pages themselves. That
+ * has been handled earlier when unmapping all the memory regions.
+ */
+static inline void clear_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
+				unsigned long addr, unsigned long end)
+{
+	if (!((addr | end) & ~PMD_MASK)) {
+		/* Only free fully aligned ranges */
+		struct page *page = pmd_page(*pmd);
+		pmd_clear(pmd);
+		dec_page_state(nr_page_table_pages);
+		tlb->mm->nr_ptes--;
+		pte_free_tlb(tlb, page);
+	}
+}
+
+static inline void clear_pmd_range(struct mmu_gather *tlb, pud_t *pud,
+				unsigned long addr, unsigned long end)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	pmd_t *empty_pmd = NULL;
+
+	pmd = pmd_offset(pud, addr);
+
+	/* Only free fully aligned ranges */
+	if (!((addr | end) & ~PUD_MASK))
+		empty_pmd = pmd;
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(pmd))
+			continue;
+		clear_pte_range(tlb, pmd, addr, next);
+	} while (pmd++, addr = next, addr != end);
+
+	if (empty_pmd) {
+		pud_clear(pud);
+		pmd_free_tlb(tlb, empty_pmd);
+	}
+}
+
+static inline void clear_pud_range(struct mmu_gather *tlb, pgd_t *pgd,
+				unsigned long addr, unsigned long end)
+{
+	pud_t *pud;
+	unsigned long next;
+	pud_t *empty_pud = NULL;
+
+	pud = pud_offset(pgd, addr);
+
+	/* Only free fully aligned ranges */
+	if (!((addr | end) & ~PGDIR_MASK))
+		empty_pud = pud;
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		clear_pmd_range(tlb, pud, addr, next);
+	} while (pud++, addr = next, addr != end);
+
+	if (empty_pud) {
+		pgd_clear(pgd);
+		pud_free_tlb(tlb, empty_pud);
+	}
+}
+
+/*
+ * This function clears user-level page tables of a process.
+ * Unlike other pagetable walks, some memory layouts might give end 0.
+ * Must be called with pagetable lock held.
+ */
+void clear_page_range(struct mmu_gather *tlb,
+				unsigned long addr, unsigned long end)
+{
+	pgd_t *pgd;
+	unsigned long next;
+
+	pgd = pgd_offset(tlb->mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		clear_pud_range(tlb, pgd, addr, next);
+	} while (pgd++, addr = next, addr != end);
+}
+
+pte_t fastcall * pte_alloc_map(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
+{
+	if (!pmd_present(*pmd)) {
+		struct page *new;
+
+		spin_unlock(&mm->page_table_lock);
+		new = pte_alloc_one(mm, address);
+		spin_lock(&mm->page_table_lock);
+		if (!new)
+			return NULL;
+		/*
+		 * Because we dropped the lock, we should re-check the
+		 * entry, as somebody else could have populated it..
+		 */
+		if (pmd_present(*pmd)) {
+			pte_free(new);
+			goto out;
+		}
+		mm->nr_ptes++;
+		inc_page_state(nr_page_table_pages);
+		pmd_populate(mm, pmd, new);
+	}
+out:
+	return pte_offset_map(pmd, address);
+}
+
+pte_t fastcall * pte_alloc_kernel(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
+{
+	if (!pmd_present(*pmd)) {
+		pte_t *new;
+
+		spin_unlock(&mm->page_table_lock);
+		new = pte_alloc_one_kernel(mm, address);
+		spin_lock(&mm->page_table_lock);
+		if (!new)
+			return NULL;
+
+		/*
+		 * Because we dropped the lock, we should re-check the
+		 * entry, as somebody else could have populated it..
+		 */
+		if (pmd_present(*pmd)) {
+			pte_free_kernel(new);
+			goto out;
+		}
+		pmd_populate_kernel(mm, pmd, new);
+	}
+out:
+	return pte_offset_kernel(pmd, address);
+}
+
+/*
+ * copy one vm_area from one task to the other. Assumes the page tables
+ * already present in the new task to be cleared in the whole range
+ * covered by this vma.
+ *
+ * dst->page_table_lock is held on entry and exit,
+ * but may be dropped within p[mg]d_alloc() and pte_alloc_map().
+ */
+
+static inline void
+copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pte_t *dst_pte, pte_t *src_pte, unsigned long vm_flags,
+		unsigned long addr)
+{
+	pte_t pte = *src_pte;
+	struct page *page;
+	unsigned long pfn;
+
+	/* pte contains position in swap or file, so copy. */
+	if (unlikely(!pte_present(pte))) {
+		if (!pte_file(pte)) {
+			swap_duplicate(pte_to_swp_entry(pte));
+			/* make sure dst_mm is on swapoff's mmlist. */
+			if (unlikely(list_empty(&dst_mm->mmlist))) {
+				spin_lock(&mmlist_lock);
+				list_add(&dst_mm->mmlist, &src_mm->mmlist);
+				spin_unlock(&mmlist_lock);
+			}
+		}
+		set_pte_at(dst_mm, addr, dst_pte, pte);
+		return;
+	}
+
+	pfn = pte_pfn(pte);
+	/* the pte points outside of valid memory, the
+	 * mapping is assumed to be good, meaningful
+	 * and not mapped via rmap - duplicate the
+	 * mapping as is.
+	 */
+	page = NULL;
+	if (pfn_valid(pfn))
+		page = pfn_to_page(pfn);
+
+	if (!page || PageReserved(page)) {
+		set_pte_at(dst_mm, addr, dst_pte, pte);
+		return;
+	}
+
+	/*
+	 * If it's a COW mapping, write protect it both
+	 * in the parent and the child
+	 */
+	if ((vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE) {
+		ptep_set_wrprotect(src_mm, addr, src_pte);
+		pte = *src_pte;
+	}
+
+	/*
+	 * If it's a shared mapping, mark it clean in
+	 * the child
+	 */
+	if (vm_flags & VM_SHARED)
+		pte = pte_mkclean(pte);
+	pte = pte_mkold(pte);
+	get_page(page);
+	inc_mm_counter(dst_mm, rss);
+	if (PageAnon(page))
+		inc_mm_counter(dst_mm, anon_rss);
+	set_pte_at(dst_mm, addr, dst_pte, pte);
+	page_dup_rmap(page);
+}
+
+static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	pte_t *src_pte, *dst_pte;
+	unsigned long vm_flags = vma->vm_flags;
+	int progress;
+
+again:
+	dst_pte = pte_alloc_map(dst_mm, dst_pmd, addr);
+	if (!dst_pte)
+		return -ENOMEM;
+	src_pte = pte_offset_map_nested(src_pmd, addr);
+
+	progress = 0;
+	spin_lock(&src_mm->page_table_lock);
+	do {
+		/*
+		 * We are holding two locks at this point - either of them
+		 * could generate latencies in another task on another CPU.
+		 */
+		if (progress >= 32 && (need_resched() ||
+		    need_lockbreak(&src_mm->page_table_lock) ||
+		    need_lockbreak(&dst_mm->page_table_lock)))
+			break;
+		if (pte_none(*src_pte)) {
+			progress++;
+			continue;
+		}
+		copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vm_flags, addr);
+		progress += 8;
+	} while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
+	spin_unlock(&src_mm->page_table_lock);
+
+	pte_unmap_nested(src_pte - 1);
+	pte_unmap(dst_pte - 1);
+	cond_resched_lock(&dst_mm->page_table_lock);
+	if (addr != end)
+		goto again;
+	return 0;
+}
+
+static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pud_t *dst_pud, pud_t *src_pud, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	pmd_t *src_pmd, *dst_pmd;
+	unsigned long next;
+
+	dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
+	if (!dst_pmd)
+		return -ENOMEM;
+	src_pmd = pmd_offset(src_pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(src_pmd))
+			continue;
+		if (copy_pte_range(dst_mm, src_mm, dst_pmd, src_pmd,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_pmd++, src_pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int copy_pud_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pgd_t *dst_pgd, pgd_t *src_pgd, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	pud_t *src_pud, *dst_pud;
+	unsigned long next;
+
+	dst_pud = pud_alloc(dst_mm, dst_pgd, addr);
+	if (!dst_pud)
+		return -ENOMEM;
+	src_pud = pud_offset(src_pgd, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(src_pud))
+			continue;
+		if (copy_pmd_range(dst_mm, src_mm, dst_pud, src_pud,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_pud++, src_pud++, addr = next, addr != end);
+	return 0;
+}
+
+int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		struct vm_area_struct *vma)
+{
+	pgd_t *src_pgd, *dst_pgd;
+	unsigned long next;
+	unsigned long addr = vma->vm_start;
+	unsigned long end = vma->vm_end;
+
+	if (is_vm_hugetlb_page(vma))
+		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
+
+	dst_pgd = pgd_offset(dst_mm, addr);
+	src_pgd = pgd_offset(src_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(src_pgd))
+			continue;
+		if (copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
+	return 0;
+}
+
+static void zap_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pte_t *pte;
+
+	pte = pte_offset_map(pmd, addr);
+	do {
+		pte_t ptent = *pte;
+		if (pte_none(ptent))
+			continue;
+		if (pte_present(ptent)) {
+			struct page *page = NULL;
+			unsigned long pfn = pte_pfn(ptent);
+			if (pfn_valid(pfn)) {
+				page = pfn_to_page(pfn);
+				if (PageReserved(page))
+					page = NULL;
+			}
+			if (unlikely(details) && page) {
+				/*
+				 * unmap_shared_mapping_pages() wants to
+				 * invalidate cache without truncating:
+				 * unmap shared but keep private pages.
+				 */
+				if (details->check_mapping &&
+				    details->check_mapping != page->mapping)
+					continue;
+				/*
+				 * Each page->index must be checked when
+				 * invalidating or truncating nonlinear.
+				 */
+				if (details->nonlinear_vma &&
+				    (page->index < details->first_index ||
+				     page->index > details->last_index))
+					continue;
+			}
+			ptent = ptep_get_and_clear(tlb->mm, addr, pte);
+			tlb_remove_tlb_entry(tlb, pte, addr);
+			if (unlikely(!page))
+				continue;
+			if (unlikely(details) && details->nonlinear_vma
+			    && linear_page_index(details->nonlinear_vma,
+						addr) != page->index)
+				set_pte_at(tlb->mm, addr, pte,
+					   pgoff_to_pte(page->index));
+			if (pte_dirty(ptent))
+				set_page_dirty(page);
+			if (PageAnon(page))
+				dec_mm_counter(tlb->mm, anon_rss);
+			else if (pte_young(ptent))
+				mark_page_accessed(page);
+			tlb->freed++;
+			page_remove_rmap(page);
+			tlb_remove_page(tlb, page);
+			continue;
+		}
+		/*
+		 * If details->check_mapping, we leave swap entries;
+		 * if details->nonlinear_vma, we leave file entries.
+		 */
+		if (unlikely(details))
+			continue;
+		if (!pte_file(ptent))
+			free_swap_and_cache(pte_to_swp_entry(ptent));
+		pte_clear(tlb->mm, addr, pte);
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	pte_unmap(pte - 1);
+}
+
+static inline void zap_pmd_range(struct mmu_gather *tlb, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(pmd))
+			continue;
+		zap_pte_range(tlb, pmd, addr, next, details);
+	} while (pmd++, addr = next, addr != end);
+}
+
+static inline void zap_pud_range(struct mmu_gather *tlb, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(pgd, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		zap_pmd_range(tlb, pud, addr, next, details);
+	} while (pud++, addr = next, addr != end);
+}
+
+static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pgd_t *pgd;
+	unsigned long next;
+
+	if (details && !details->check_mapping && !details->nonlinear_vma)
+		details = NULL;
+
+	BUG_ON(addr >= end);
+	tlb_start_vma(tlb, vma);
+	pgd = pgd_offset(vma->vm_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		zap_pud_range(tlb, pgd, addr, next, details);
+	} while (pgd++, addr = next, addr != end);
+	tlb_end_vma(tlb, vma);
+}
+
+#ifdef CONFIG_PREEMPT
+# define ZAP_BLOCK_SIZE	(8 * PAGE_SIZE)
+#else
+/* No preempt: go for improved straight-line efficiency */
+# define ZAP_BLOCK_SIZE	(1024 * PAGE_SIZE)
+#endif
+
+/**
+ * unmap_vmas - unmap a range of memory covered by a list of vma's
+ * @tlbp: address of the caller's struct mmu_gather
+ * @mm: the controlling mm_struct
+ * @vma: the starting vma
+ * @start_addr: virtual address at which to start unmapping
+ * @end_addr: virtual address at which to end unmapping
+ * @nr_accounted: Place number of unmapped pages in vm-accountable vma's here
+ * @details: details of nonlinear truncation or shared cache invalidation
+ *
+ * Returns the number of vma's which were covered by the unmapping.
+ *
+ * Unmap all pages in the vma list.  Called under page_table_lock.
+ *
+ * We aim to not hold page_table_lock for too long (for scheduling latency
+ * reasons).  So zap pages in ZAP_BLOCK_SIZE bytecounts.  This means we need to
+ * return the ending mmu_gather to the caller.
+ *
+ * Only addresses between `start' and `end' will be unmapped.
+ *
+ * The VMA list must be sorted in ascending virtual address order.
+ *
+ * unmap_vmas() assumes that the caller will flush the whole unmapped address
+ * range after unmap_vmas() returns.  So the only responsibility here is to
+ * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
+ * drops the lock and schedules.
+ */
+int unmap_vmas(struct mmu_gather **tlbp, struct mm_struct *mm,
+		struct vm_area_struct *vma, unsigned long start_addr,
+		unsigned long end_addr, unsigned long *nr_accounted,
+		struct zap_details *details)
+{
+	unsigned long zap_bytes = ZAP_BLOCK_SIZE;
+	unsigned long tlb_start = 0;	/* For tlb_finish_mmu */
+	int tlb_start_valid = 0;
+	int ret = 0;
+	spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
+	int fullmm = tlb_is_full_mm(*tlbp);
+
+	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
+		unsigned long start;
+		unsigned long end;
+
+		start = max(vma->vm_start, start_addr);
+		if (start >= vma->vm_end)
+			continue;
+		end = min(vma->vm_end, end_addr);
+		if (end <= vma->vm_start)
+			continue;
+
+		if (vma->vm_flags & VM_ACCOUNT)
+			*nr_accounted += (end - start) >> PAGE_SHIFT;
+
+		ret++;
+		while (start != end) {
+			unsigned long block;
+
+			if (!tlb_start_valid) {
+				tlb_start = start;
+				tlb_start_valid = 1;
+			}
+
+			if (is_vm_hugetlb_page(vma)) {
+				block = end - start;
+				unmap_hugepage_range(vma, start, end);
+			} else {
+				block = min(zap_bytes, end - start);
+				unmap_page_range(*tlbp, vma, start,
+						start + block, details);
+			}
+
+			start += block;
+			zap_bytes -= block;
+			if ((long)zap_bytes > 0)
+				continue;
+
+			tlb_finish_mmu(*tlbp, tlb_start, start);
+
+			if (need_resched() ||
+				need_lockbreak(&mm->page_table_lock) ||
+				(i_mmap_lock && need_lockbreak(i_mmap_lock))) {
+				if (i_mmap_lock) {
+					/* must reset count of rss freed */
+					*tlbp = tlb_gather_mmu(mm, fullmm);
+					details->break_addr = start;
+					goto out;
+				}
+				spin_unlock(&mm->page_table_lock);
+				cond_resched();
+				spin_lock(&mm->page_table_lock);
+			}
+
+			*tlbp = tlb_gather_mmu(mm, fullmm);
+			tlb_start_valid = 0;
+			zap_bytes = ZAP_BLOCK_SIZE;
+		}
+	}
+out:
+	return ret;
+}
+
+/**
+ * zap_page_range - remove user pages in a given range
+ * @vma: vm_area_struct holding the applicable pages
+ * @address: starting address of pages to zap
+ * @size: number of bytes to zap
+ * @details: details of nonlinear truncation or shared cache invalidation
+ */
+void zap_page_range(struct vm_area_struct *vma, unsigned long address,
+		unsigned long size, struct zap_details *details)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct mmu_gather *tlb;
+	unsigned long end = address + size;
+	unsigned long nr_accounted = 0;
+
+	if (is_vm_hugetlb_page(vma)) {
+		zap_hugepage_range(vma, address, size);
+		return;
+	}
+
+	lru_add_drain();
+	spin_lock(&mm->page_table_lock);
+	tlb = tlb_gather_mmu(mm, 0);
+	unmap_vmas(&tlb, mm, vma, address, end, &nr_accounted, details);
+	tlb_finish_mmu(tlb, address, end);
+	spin_unlock(&mm->page_table_lock);
+}
+
+/*
+ * Do a quick page-table lookup for a single page.
+ * mm->page_table_lock must be held.
+ */
+static struct page *
+__follow_page(struct mm_struct *mm, unsigned long address, int read, int write)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep, pte;
+	unsigned long pfn;
+	struct page *page;
+
+	page = follow_huge_addr(mm, address, write);
+	if (! IS_ERR(page))
+		return page;
+
+	pgd = pgd_offset(mm, address);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto out;
+
+	pud = pud_offset(pgd, address);
+	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+		goto out;
+	
+	pmd = pmd_offset(pud, address);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto out;
+	if (pmd_huge(*pmd))
+		return follow_huge_pmd(mm, address, pmd, write);
+
+	ptep = pte_offset_map(pmd, address);
+	if (!ptep)
+		goto out;
+
+	pte = *ptep;
+	pte_unmap(ptep);
+	if (pte_present(pte)) {
+		if (write && !pte_write(pte))
+			goto out;
+		if (read && !pte_read(pte))
+			goto out;
+		pfn = pte_pfn(pte);
+		if (pfn_valid(pfn)) {
+			page = pfn_to_page(pfn);
+			if (write && !pte_dirty(pte) && !PageDirty(page))
+				set_page_dirty(page);
+			mark_page_accessed(page);
+			return page;
+		}
+	}
+
+out:
+	return NULL;
+}
+
+struct page *
+follow_page(struct mm_struct *mm, unsigned long address, int write)
+{
+	return __follow_page(mm, address, /*read*/0, write);
+}
+
+int
+check_user_page_readable(struct mm_struct *mm, unsigned long address)
+{
+	return __follow_page(mm, address, /*read*/1, /*write*/0) != NULL;
+}
+
+EXPORT_SYMBOL(check_user_page_readable);
+
+/* 
+ * Given a physical address, is there a useful struct page pointing to
+ * it?  This may become more complex in the future if we start dealing
+ * with IO-aperture pages for direct-IO.
+ */
+
+static inline struct page *get_page_map(struct page *page)
+{
+	if (!pfn_valid(page_to_pfn(page)))
+		return NULL;
+	return page;
+}
+
+
+static inline int
+untouched_anonymous_page(struct mm_struct* mm, struct vm_area_struct *vma,
+			 unsigned long address)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	/* Check if the vma is for an anonymous mapping. */
+	if (vma->vm_ops && vma->vm_ops->nopage)
+		return 0;
+
+	/* Check if page directory entry exists. */
+	pgd = pgd_offset(mm, address);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		return 1;
+
+	pud = pud_offset(pgd, address);
+	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+		return 1;
+
+	/* Check if page middle directory entry exists. */
+	pmd = pmd_offset(pud, address);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		return 1;
+
+	/* There is a pte slot for 'address' in 'mm'. */
+	return 0;
+}
+
+
+int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, int len, int write, int force,
+		struct page **pages, struct vm_area_struct **vmas)
+{
+	int i;
+	unsigned int flags;
+
+	/* 
+	 * Require read or write permissions.
+	 * If 'force' is set, we only require the "MAY" flags.
+	 */
+	flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
+	flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
+	i = 0;
+
+	do {
+		struct vm_area_struct *	vma;
+
+		vma = find_extend_vma(mm, start);
+		if (!vma && in_gate_area(tsk, start)) {
+			unsigned long pg = start & PAGE_MASK;
+			struct vm_area_struct *gate_vma = get_gate_vma(tsk);
+			pgd_t *pgd;
+			pud_t *pud;
+			pmd_t *pmd;
+			pte_t *pte;
+			if (write) /* user gate pages are read-only */
+				return i ? : -EFAULT;
+			if (pg > TASK_SIZE)
+				pgd = pgd_offset_k(pg);
+			else
+				pgd = pgd_offset_gate(mm, pg);
+			BUG_ON(pgd_none(*pgd));
+			pud = pud_offset(pgd, pg);
+			BUG_ON(pud_none(*pud));
+			pmd = pmd_offset(pud, pg);
+			BUG_ON(pmd_none(*pmd));
+			pte = pte_offset_map(pmd, pg);
+			BUG_ON(pte_none(*pte));
+			if (pages) {
+				pages[i] = pte_page(*pte);
+				get_page(pages[i]);
+			}
+			pte_unmap(pte);
+			if (vmas)
+				vmas[i] = gate_vma;
+			i++;
+			start += PAGE_SIZE;
+			len--;
+			continue;
+		}
+
+		if (!vma || (vma->vm_flags & VM_IO)
+				|| !(flags & vma->vm_flags))
+			return i ? : -EFAULT;
+
+		if (is_vm_hugetlb_page(vma)) {
+			i = follow_hugetlb_page(mm, vma, pages, vmas,
+						&start, &len, i);
+			continue;
+		}
+		spin_lock(&mm->page_table_lock);
+		do {
+			struct page *map;
+			int lookup_write = write;
+
+			cond_resched_lock(&mm->page_table_lock);
+			while (!(map = follow_page(mm, start, lookup_write))) {
+				/*
+				 * Shortcut for anonymous pages. We don't want
+				 * to force the creation of pages tables for
+				 * insanly big anonymously mapped areas that
+				 * nobody touched so far. This is important
+				 * for doing a core dump for these mappings.
+				 */
+				if (!lookup_write &&
+				    untouched_anonymous_page(mm,vma,start)) {
+					map = ZERO_PAGE(start);
+					break;
+				}
+				spin_unlock(&mm->page_table_lock);
+				switch (handle_mm_fault(mm,vma,start,write)) {
+				case VM_FAULT_MINOR:
+					tsk->min_flt++;
+					break;
+				case VM_FAULT_MAJOR:
+					tsk->maj_flt++;
+					break;
+				case VM_FAULT_SIGBUS:
+					return i ? i : -EFAULT;
+				case VM_FAULT_OOM:
+					return i ? i : -ENOMEM;
+				default:
+					BUG();
+				}
+				/*
+				 * Now that we have performed a write fault
+				 * and surely no longer have a shared page we
+				 * shouldn't write, we shouldn't ignore an
+				 * unwritable page in the page table if
+				 * we are forcing write access.
+				 */
+				lookup_write = write && !force;
+				spin_lock(&mm->page_table_lock);
+			}
+			if (pages) {
+				pages[i] = get_page_map(map);
+				if (!pages[i]) {
+					spin_unlock(&mm->page_table_lock);
+					while (i--)
+						page_cache_release(pages[i]);
+					i = -EFAULT;
+					goto out;
+				}
+				flush_dcache_page(pages[i]);
+				if (!PageReserved(pages[i]))
+					page_cache_get(pages[i]);
+			}
+			if (vmas)
+				vmas[i] = vma;
+			i++;
+			start += PAGE_SIZE;
+			len--;
+		} while(len && start < vma->vm_end);
+		spin_unlock(&mm->page_table_lock);
+	} while(len);
+out:
+	return i;
+}
+
+EXPORT_SYMBOL(get_user_pages);
+
+static int zeromap_pte_range(struct mm_struct *mm, pmd_t *pmd,
+			unsigned long addr, unsigned long end, pgprot_t prot)
+{
+	pte_t *pte;
+
+	pte = pte_alloc_map(mm, pmd, addr);
+	if (!pte)
+		return -ENOMEM;
+	do {
+		pte_t zero_pte = pte_wrprotect(mk_pte(ZERO_PAGE(addr), prot));
+		BUG_ON(!pte_none(*pte));
+		set_pte_at(mm, addr, pte, zero_pte);
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	pte_unmap(pte - 1);
+	return 0;
+}
+
+static inline int zeromap_pmd_range(struct mm_struct *mm, pud_t *pud,
+			unsigned long addr, unsigned long end, pgprot_t prot)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return -ENOMEM;
+	do {
+		next = pmd_addr_end(addr, end);
+		if (zeromap_pte_range(mm, pmd, addr, next, prot))
+			return -ENOMEM;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int zeromap_pud_range(struct mm_struct *mm, pgd_t *pgd,
+			unsigned long addr, unsigned long end, pgprot_t prot)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_alloc(mm, pgd, addr);
+	if (!pud)
+		return -ENOMEM;
+	do {
+		next = pud_addr_end(addr, end);
+		if (zeromap_pmd_range(mm, pud, addr, next, prot))
+			return -ENOMEM;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+int zeromap_page_range(struct vm_area_struct *vma,
+			unsigned long addr, unsigned long size, pgprot_t prot)
+{
+	pgd_t *pgd;
+	unsigned long next;
+	unsigned long end = addr + size;
+	struct mm_struct *mm = vma->vm_mm;
+	int err;
+
+	BUG_ON(addr >= end);
+	pgd = pgd_offset(mm, addr);
+	flush_cache_range(vma, addr, end);
+	spin_lock(&mm->page_table_lock);
+	do {
+		next = pgd_addr_end(addr, end);
+		err = zeromap_pud_range(mm, pgd, addr, next, prot);
+		if (err)
+			break;
+	} while (pgd++, addr = next, addr != end);
+	spin_unlock(&mm->page_table_lock);
+	return err;
+}
+
+/*
+ * maps a range of physical memory into the requested pages. the old
+ * mappings are removed. any references to nonexistent pages results
+ * in null mappings (currently treated as "copy-on-access")
+ */
+static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pte_t *pte;
+
+	pte = pte_alloc_map(mm, pmd, addr);
+	if (!pte)
+		return -ENOMEM;
+	do {
+		BUG_ON(!pte_none(*pte));
+		if (!pfn_valid(pfn) || PageReserved(pfn_to_page(pfn)))
+			set_pte_at(mm, addr, pte, pfn_pte(pfn, prot));
+		pfn++;
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	pte_unmap(pte - 1);
+	return 0;
+}
+
+static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return -ENOMEM;
+	do {
+		next = pmd_addr_end(addr, end);
+		if (remap_pte_range(mm, pmd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot))
+			return -ENOMEM;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int remap_pud_range(struct mm_struct *mm, pgd_t *pgd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pud = pud_alloc(mm, pgd, addr);
+	if (!pud)
+		return -ENOMEM;
+	do {
+		next = pud_addr_end(addr, end);
+		if (remap_pmd_range(mm, pud, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot))
+			return -ENOMEM;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+/*  Note: this is only safe if the mm semaphore is held when called. */
+int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		    unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	pgd_t *pgd;
+	unsigned long next;
+	unsigned long end = addr + size;
+	struct mm_struct *mm = vma->vm_mm;
+	int err;
+
+	/*
+	 * Physically remapped pages are special. Tell the
+	 * rest of the world about it:
+	 *   VM_IO tells people not to look at these pages
+	 *	(accesses can have side effects).
+	 *   VM_RESERVED tells swapout not to try to touch
+	 *	this region.
+	 */
+	vma->vm_flags |= VM_IO | VM_RESERVED;
+
+	BUG_ON(addr >= end);
+	pfn -= addr >> PAGE_SHIFT;
+	pgd = pgd_offset(mm, addr);
+	flush_cache_range(vma, addr, end);
+	spin_lock(&mm->page_table_lock);
+	do {
+		next = pgd_addr_end(addr, end);
+		err = remap_pud_range(mm, pgd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			break;
+	} while (pgd++, addr = next, addr != end);
+	spin_unlock(&mm->page_table_lock);
+	return err;
+}
+EXPORT_SYMBOL(remap_pfn_range);
+
+/*
+ * Do pte_mkwrite, but only if the vma says VM_WRITE.  We do this when
+ * servicing faults for write access.  In the normal case, do always want
+ * pte_mkwrite.  But get_user_pages can cause write faults for mappings
+ * that do not have writing enabled, when used by access_process_vm.
+ */
+static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_flags & VM_WRITE))
+		pte = pte_mkwrite(pte);
+	return pte;
+}
+
+/*
+ * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
+ */
+static inline void break_cow(struct vm_area_struct * vma, struct page * new_page, unsigned long address, 
+		pte_t *page_table)
+{
+	pte_t entry;
+
+	entry = maybe_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot)),
+			      vma);
+	ptep_establish(vma, address, page_table, entry);
+	update_mmu_cache(vma, address, entry);
+	lazy_mmu_prot_update(entry);
+}
+
+/*
+ * This routine handles present pages, when users try to write
+ * to a shared page. It is done by copying the page to a new address
+ * and decrementing the shared-page counter for the old page.
+ *
+ * Goto-purists beware: the only reason for goto's here is that it results
+ * in better assembly code.. The "default" path will see no jumps at all.
+ *
+ * Note that this routine assumes that the protection checks have been
+ * done by the caller (the low-level page fault routine in most cases).
+ * Thus we can safely just mark it writable once we've done any necessary
+ * COW.
+ *
+ * We also mark the page dirty at this point even though the page will
+ * change only once the write actually happens. This avoids a few races,
+ * and potentially makes it more efficient.
+ *
+ * We hold the mm semaphore and the page_table_lock on entry and exit
+ * with the page_table_lock released.
+ */
+static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
+	unsigned long address, pte_t *page_table, pmd_t *pmd, pte_t pte)
+{
+	struct page *old_page, *new_page;
+	unsigned long pfn = pte_pfn(pte);
+	pte_t entry;
+
+	if (unlikely(!pfn_valid(pfn))) {
+		/*
+		 * This should really halt the system so it can be debugged or
+		 * at least the kernel stops what it's doing before it corrupts
+		 * data, but for the moment just pretend this is OOM.
+		 */
+		pte_unmap(page_table);
+		printk(KERN_ERR "do_wp_page: bogus page at address %08lx\n",
+				address);
+		spin_unlock(&mm->page_table_lock);
+		return VM_FAULT_OOM;
+	}
+	old_page = pfn_to_page(pfn);
+
+	if (!TestSetPageLocked(old_page)) {
+		int reuse = can_share_swap_page(old_page);
+		unlock_page(old_page);
+		if (reuse) {
+			flush_cache_page(vma