From 4df1d488d823dd1231459faa9aebfa7764706e9e Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Tue, 20 Jan 2009 23:17:30 -0200
Subject: [PATCH 44/54] [PATCH 40/54] ksm

KSM tree implementation with kprobes wp_notifier.

Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
RH-Upstream-status: pending
---
 kernel/ksm/Kbuild                   |    3 +
 kernel/ksm/external-module-compat.h |  377 ++++++++++
 kernel/ksm/ksm.c                    | 1367 +++++++++++++++++++++++++++++++++++
 kernel/ksm/ksm.h                    |   84 +++
 kernel/ksm/wp_notifier.c            |   60 ++
 kernel/ksm/wp_notifier.h            |   12 +
 6 files changed, 1903 insertions(+), 0 deletions(-)
 create mode 100644 kernel/ksm/Kbuild
 create mode 100644 kernel/ksm/Makefile
 create mode 100644 kernel/ksm/external-module-compat.h
 create mode 100644 kernel/ksm/ksm.c
 create mode 100644 kernel/ksm/ksm.h
 create mode 100644 kernel/ksm/wp_notifier.c
 create mode 100644 kernel/ksm/wp_notifier.h

diff --git a/kernel/ksm/Kbuild b/kernel/ksm/Kbuild
new file mode 100644
index 0000000..06b3a63
--- /dev/null
+++ b/kernel/ksm/Kbuild
@@ -0,0 +1,3 @@
+obj-m := ksm-mem.o
+ksm-mem-objs := ksm.o
+ksm-mem-objs := ksm.o wp_notifier.o
diff --git a/kernel/ksm/Makefile b/kernel/ksm/Makefile
new file mode 100644
index 0000000..e69de29
diff --git a/kernel/ksm/external-module-compat.h b/kernel/ksm/external-module-compat.h
new file mode 100644
index 0000000..032dc8e
--- /dev/null
+++ b/kernel/ksm/external-module-compat.h
@@ -0,0 +1,377 @@
+
+/*
+ * Compatibility header for building as an external module.
+ */
+
+/*
+ * Avoid picking up the kernel's kvm.h in case we have a newer one.
+ */
+
+#include <linux/compiler.h>
+#include <linux/version.h>
+#include <linux/string.h>
+#include <linux/cpu.h>
+#include <linux/list.h>
+#include <asm/processor.h>
+#include <linux/hrtimer.h>
+#include <asm/bitops.h>
+#include <linux/mm.h>
+#include <linux/rmap.h>
+#include <asm/tlbflush.h>
+#include <linux/module.h>
+#include <asm/cacheflush.h>
+#include <asm-generic/pgtable.h>
+
+/*
+ * 2.6.16 does not have GFP_NOWAIT
+ */
+
+#include <linux/gfp.h>
+
+void kvm_ksm_set_pte(struct mm_struct *mm, unsigned long address, pte_t pte);
+int kvm_ksm_spte_count(struct mm_struct *mm,
+		       unsigned long address);
+
+#define list_first_entry(ptr, type, member) \
+        list_entry((ptr)->next, type, member)
+
+static struct anon_vma *page_lock_anon_vma(struct page *page)
+{
+	struct anon_vma *anon_vma;
+	unsigned long anon_mapping;
+
+	rcu_read_lock();
+	anon_mapping = (unsigned long) page->mapping;
+	if (!(anon_mapping & PAGE_MAPPING_ANON))
+		goto out;
+	if (!page_mapped(page))
+		goto out;
+
+	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
+	spin_lock(&anon_vma->lock);
+	return anon_vma;
+out:
+	rcu_read_unlock();
+	return NULL;
+}
+
+static void page_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+	spin_unlock(&anon_vma->lock);
+	rcu_read_unlock();
+}
+
+/*
+ * At what user virtual address is page expected in @vma?
+ * Returns virtual address or -EFAULT if page's index/offset is not
+ * within the range mapped the @vma.
+ */
+static inline unsigned long
+vma_address(struct page *page, struct vm_area_struct *vma)
+{
+	pgoff_t pgoff = page->index;
+	unsigned long address;
+
+	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+	if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
+		/* page should be within @vma mapping range */
+		return -EFAULT;
+	}
+	return address;
+}
+
+/*
+ * At what user virtual address is page expected in vma? checking that the
+ * page matches the vma: currently only used on anon pages, by unuse_vma;
+ */
+unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
+{
+	if (PageAnon(page)) {
+		if ((void *)vma->anon_vma !=
+		    (void *)page->mapping - PAGE_MAPPING_ANON)
+			return -EFAULT;
+	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
+		if (!vma->vm_file ||
+		    vma->vm_file->f_mapping != page->mapping)
+			return -EFAULT;
+	} else
+		return -EFAULT;
+	return vma_address(page, vma);
+}
+
+/*
+ * Check that @page is mapped at @address into @mm.
+ *
+ * On success returns with pte mapped and locked.
+ */
+pte_t *page_check_address(struct page *page, struct mm_struct *mm,
+			  unsigned long address, spinlock_t **ptlp)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+	spinlock_t *ptl;
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		return NULL;
+
+	pud = pud_offset(pgd, address);
+	if (!pud_present(*pud))
+		return NULL;
+
+	pmd = pmd_offset(pud, address);
+	if (!pmd_present(*pmd))
+		return NULL;
+
+	pte = pte_offset_map(pmd, address);
+	/* Make a quick check before getting the lock */
+	if (!pte_present(*pte)) {
+		pte_unmap(pte);
+		return NULL;
+	}
+
+	ptl = pte_lockptr(mm, pmd);
+	spin_lock(ptl);
+	if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
+		*ptlp = ptl;
+		return pte;
+	}
+	pte_unmap_unlock(pte, ptl);
+	return NULL;
+}
+
+void page_remove_rmap_old(struct page *page, struct vm_area_struct *vma)
+{
+	if (atomic_add_negative(-1, &page->_mapcount)) {
+		if (unlikely(page_mapcount(page) < 0)) {
+			printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)\n", page_mapcount(page));
+			printk (KERN_EMERG "  page pfn = %lx\n", page_to_pfn(page));
+			printk (KERN_EMERG "  page->flags = %lx\n", page->flags);
+			printk (KERN_EMERG "  page->count = %x\n", page_count(page));
+			printk (KERN_EMERG "  page->mapping = %p\n", page->mapping);
+			BUG();
+		}
+
+		/*
+		 * It would be tidy to reset the PageAnon mapping here,
+		 * but that might overwrite a racing page_add_anon_rmap
+		 * which increments mapcount after us but sets mapping
+		 * before us: so leave the reset to free_hot_cold_page,
+		 * and remember that it's only reliable while mapped.
+		 * Leaving it set also helps swapoff to reinstate ptes
+		 * faster for those pages still in swapcache.
+		 */
+		__dec_zone_page_state(page,
+				PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
+	}
+}
+
+void page_add_file_rmap_old(struct page *page)
+{
+	if (atomic_inc_and_test(&page->_mapcount))
+		__inc_zone_page_state(page, NR_FILE_MAPPED);
+}
+
+static int page_wrprotect_one(struct page *page, struct vm_area_struct *vma,
+			      int *odirect_sync, int count_offset)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long address;
+	pte_t *pte;
+	spinlock_t *ptl;
+	int ret = 0;
+
+	address = vma_address(page, vma);
+	if (address == -EFAULT)
+		goto out;
+
+	pte = page_check_address(page, mm, address, &ptl);
+	if (!pte)
+		goto out;
+
+	if (pte_write(*pte)) {
+		pte_t entry;
+
+		/*
+		 * this is needed here to balance the mapcount of the page
+		 */
+		count_offset += kvm_ksm_spte_count(mm, address);
+		
+		/*
+		 * Check that no O_DIRECT or similar I/O is in progress on the
+		 * page
+		 */
+		if ((page_mapcount(page) + count_offset) != page_count(page)) {
+			*odirect_sync = 0;
+			goto out_unlock;
+		}
+
+		flush_cache_page(vma, address, pte_pfn(*pte));
+		entry = ptep_clear_flush(vma, address, pte);
+		entry = pte_wrprotect(entry);
+		set_pte_at(mm, address, pte, entry);
+		BUG_ON(pte_write(entry));
+		kvm_ksm_set_pte(mm, address, entry);
+	}
+	ret = 1;
+
+out_unlock:
+	pte_unmap_unlock(pte, ptl);
+out:
+	return ret;
+}
+
+static int page_wrprotect_anon(struct page *page, int *odirect_sync,
+			       int count_offset)
+{
+	struct vm_area_struct *vma;
+	struct anon_vma *anon_vma;
+	int ret = 0;
+
+	anon_vma = page_lock_anon_vma(page);
+	if (!anon_vma)
+		return ret;
+
+	/*
+	 * If the page is inside the swap cache, its _count number was
+	 * increased by one, therefore we have to increase count_offset by one.
+	 */
+	if (PageSwapCache(page))
+		count_offset++;
+
+	list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
+		ret += page_wrprotect_one(page, vma, odirect_sync,
+					  count_offset);
+
+	page_unlock_anon_vma(anon_vma);
+
+	return ret;
+}
+
+/**
+ * page_wrprotect - set all ptes pointing to a page as readonly
+ * @page:         the page to set as readonly
+ * @odirect_sync: boolean value that is set to 0 when some of the ptes were not
+ *                marked as readonly beacuse page_wrprotect_one() was not able
+ *                to mark this ptes as readonly without opening window to a race
+ *                with odirect
+ * @count_offset: number of times page_wrprotect() caller had called get_page()
+ *                on the page
+ *
+ * returns the number of ptes which were marked as readonly.
+ * (ptes that were readonly before this function was called are counted as well)
+ */
+int page_wrprotect(struct page *page, int *odirect_sync, int count_offset)
+{
+	int ret = 0;
+
+	/*
+	 * Page lock is needed for anon pages for the PageSwapCache check,
+	 * and for page_mapping for filebacked pages
+	 */
+	BUG_ON(!PageLocked(page));
+
+	*odirect_sync = 1;
+	if (PageAnon(page))
+		ret = page_wrprotect_anon(page, odirect_sync, count_offset);
+
+	return ret;
+}
+
+/**
+ * replace_page - replace page in vma with new page
+ * @vma:      vma that hold the pte oldpage is pointed by.
+ * @oldpage:  the page we are replacing with newpage
+ * @newpage:  the page we replace oldpage with
+ * @orig_pte: the original value of the pte
+ * @prot: page protection bits
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ *
+ * Note: @newpage must not be an anonymous page because replace_page() does
+ * not change the mapping of @newpage to have the same values as @oldpage.
+ * @newpage can be mapped in several vmas at different offsets (page->index).
+ */
+int replace_page(struct vm_area_struct *vma, struct page *oldpage,
+		 struct page *newpage, pte_t orig_pte, pgprot_t prot)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep;
+	pte_t new_pte;
+	spinlock_t *ptl;
+	unsigned long addr;
+	int ret;
+
+	BUG_ON(PageAnon(newpage));
+
+	ret = -EFAULT;
+	addr = page_address_in_vma(oldpage, vma);
+	if (addr == -EFAULT)
+		goto out;
+
+	pgd = pgd_offset(mm, addr);
+	if (!pgd_present(*pgd))
+		goto out;
+
+	pud = pud_offset(pgd, addr);
+	if (!pud_present(*pud))
+		goto out;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		goto out;
+
+	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
+	if (!ptep)
+		goto out;
+
+	if (!pte_same(*ptep, orig_pte)) {
+		pte_unmap_unlock(ptep, ptl);
+		goto out;
+	}
+
+	ret = 0;
+	get_page(newpage);
+	page_add_file_rmap_old(newpage);
+
+	flush_cache_page(vma, addr, pte_pfn(*ptep));
+	ptep_clear_flush(vma, addr, ptep);
+	new_pte = mk_pte(newpage, prot);
+	set_pte_at(mm, addr, ptep, new_pte);
+	update_mmu_cache(vma, addr, new_pte);
+	BUG_ON(pte_write(new_pte));
+	kvm_ksm_set_pte(mm, addr, new_pte);
+
+	page_remove_rmap_old(oldpage, vma);
+	if (PageAnon(oldpage)) {
+		dec_mm_counter(mm, anon_rss);
+		inc_mm_counter(mm, file_rss);
+	}
+	put_page(oldpage);
+
+	pte_unmap_unlock(ptep, ptl);
+out:
+	return ret;
+}
+
+
+#include <linux/smp.h>
+
+/* HRTIMER_MODE_ABS started life with a different name */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,21)
+#define HRTIMER_MODE_ABS HRTIMER_ABS
+#endif
+
+/* __mmdrop() is not exported before 2.6.25 */
+#include <linux/sched.h>
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,25)
+
+#define mmdrop(x) do { (void)(x); } while (0)
+
+#endif
diff --git a/kernel/ksm/ksm.c b/kernel/ksm/ksm.c
new file mode 100644
index 0000000..8d1fb20
--- /dev/null
+++ b/kernel/ksm/ksm.c
@@ -0,0 +1,1367 @@
+/*
+ * Memory merging driver for Linux
+ *
+ * This module enables dynamic sharing of identical pages found in different
+ * memory areas, even if they are not shared by fork()
+ *
+ * Copyright (C) 2008 Red Hat, Inc.
+ * Authors:
+ *	Izik Eidus
+ *	Andrea Arcangeli
+ *	Chris Wright
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ */
+
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/vmalloc.h>
+#include <linux/file.h>
+#include <linux/mman.h>
+#include <linux/sched.h>
+#include <linux/rwsem.h>
+#include <linux/pagemap.h>
+#include <linux/sched.h>
+#include <linux/rmap.h>
+#include <linux/spinlock.h>
+#include <linux/jhash.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/wait.h>
+#include <linux/scatterlist.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/rbtree.h>
+#include <linux/anon_inodes.h>
+
+#include <asm/tlbflush.h>
+
+#include "ksm.h"
+#include "wp_notifier.h"
+#include "external-module-compat.h"
+
+#define KSM_MINOR 234
+
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+static int rmap_hash_size;
+module_param(rmap_hash_size, int, 0);
+MODULE_PARM_DESC(rmap_hash_size, "Hash table size for the reverse mapping");
+
+/*
+ * ksm_mem_slot - hold information for an userspace scanning range
+ * (the scanning for this region will be from addr untill addr +
+ *  npages * PAGE_SIZE inside mm)
+ */
+struct ksm_mem_slot {
+	struct list_head link;
+	struct list_head sma_link;
+	struct mm_struct *mm;
+	unsigned long addr;	/* the begining of the virtual address */
+	int npages;		/* number of pages to share */
+};
+
+/*
+ * ksm_sma - shared memory area, each process have its own sma that contain the
+ * information about the slots that it own
+ */
+struct ksm_sma {
+	struct list_head sma_slots;
+};
+
+/**
+ * struct ksm_scan - cursor for scanning
+ * @slot_index: the current slot we are scanning
+ * @page_index: the page inside the sma that is currently being scanned
+ *
+ * ksm uses it to know what are the next pages it need to scan
+ */
+struct ksm_scan {
+	struct ksm_mem_slot *slot_index;
+	unsigned long page_index;
+};
+
+/*
+ * Few notes about ksm scanning progress (make it easier to understand the
+ * structures below):
+ *
+ * In order to reduce excessive scanning, pages are sorted into the hash
+ * table, page_hash.  After a page is inserted into the hash table, its
+ * contents may have changed.  In this case, ksm must remove the page from
+ * the hash table and potentially rehash it.  Ksm uses a reverse mapping,
+ * rmap_hash, to efficiently manage this.
+ */
+
+struct rmap_item;
+
+/*
+ * tree_item - object of the write protected pages tree
+ */
+struct tree_item {
+	struct rb_node node;
+	struct rmap_item *rmap_item;
+};
+
+/*
+ * rmap_item - object of the rmap_hash hash table
+ * (it is holding the previous hash value (oldindex),
+ *  pointer into the page_hash_item, and pointer into the tree_item)
+ */
+struct rmap_item {
+	struct hlist_node link;
+	struct mm_struct *mm;
+	unsigned long address;
+	unsigned int oldchecksum; /* old checksum value */
+	unsigned char stable_tree; // 1 stable_tree 0 unstable tree
+	struct tree_item *tree_item;
+	struct rmap_item *next;
+	struct rmap_item *prev;
+};
+
+/*
+ * slots is linked list that hold all the memory regions that were registred
+ * to be scanned.
+ */
+static LIST_HEAD(slots);
+static DECLARE_RWSEM(slots_lock);
+
+struct rb_root root_stable_tree = RB_ROOT;
+struct rb_root root_unstable_tree = RB_ROOT;
+
+static int nrmaps_hash;
+/* rmap_hash hash table */
+static struct hlist_head *rmap_hash;
+
+static struct kmem_cache *tree_item_cache;
+static struct kmem_cache *rmap_item_cache;
+
+static int kthread_sleep; /* sleep time of the kernel thread */
+static int kthread_pages_to_scan; /* npages to scan for the kernel thread */
+static struct ksm_scan kthread_ksm_scan;
+static int ksmd_flags;
+static struct task_struct *kthread;
+static DECLARE_WAIT_QUEUE_HEAD(kthread_wait);
+static DECLARE_RWSEM(kthread_lock);
+
+static int ksm_slab_init(void)
+{
+	int ret = -ENOMEM;
+
+	tree_item_cache = KMEM_CACHE(tree_item, 0);
+	if (!tree_item_cache)
+		goto out;
+
+	rmap_item_cache = KMEM_CACHE(rmap_item, 0);
+	if (!rmap_item_cache)
+		goto out_free;
+
+	return 0;
+
+out_free:
+	kmem_cache_destroy(tree_item_cache);
+out:
+	return ret;
+}
+
+static void ksm_slab_free(void)
+{
+	kmem_cache_destroy(rmap_item_cache);
+	kmem_cache_destroy(tree_item_cache);
+}
+
+static inline struct tree_item *alloc_tree_item(void)
+{
+	return kmem_cache_zalloc(tree_item_cache, GFP_KERNEL);
+}
+
+static void free_tree_item(struct tree_item *tree_item)
+{
+	kmem_cache_free(tree_item_cache, tree_item);
+}
+
+static inline struct rmap_item *alloc_rmap_item(void)
+{
+	return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
+}
+
+static inline void free_rmap_item(struct rmap_item *rmap_item)
+{
+	kmem_cache_free(rmap_item_cache, rmap_item);
+}
+
+/*
+ * PageKsm - this type of pages are the write protected pages that ksm map
+ * into multiple vmas (this is the "shared page")
+ * this page was allocated using alloc_page(), every pte that pointing to it
+ * is always write protected (therefore its data content cant ever be changed)
+ * and this page cant be swapped.
+ */
+static inline int PageKsm(struct page *page)
+{
+	return !PageAnon(page);
+}
+
+static int rmap_hash_init(void)
+{
+	if (!rmap_hash_size) {
+		struct sysinfo sinfo;
+
+		si_meminfo(&sinfo);
+		rmap_hash_size = sinfo.totalram / 10;
+	}
+	nrmaps_hash = rmap_hash_size;
+	rmap_hash = vmalloc(nrmaps_hash * sizeof(struct hlist_head));
+	if (!rmap_hash)
+		return -ENOMEM;
+	memset(rmap_hash, 0, nrmaps_hash * sizeof(struct hlist_head));
+	return 0;
+}
+
+static void rmap_hash_free(void)
+{
+	int i;
+	struct hlist_head *bucket;
+	struct hlist_node *node, *n;
+	struct rmap_item *rmap_item;
+
+	for (i = 0; i < nrmaps_hash; ++i) {
+		bucket = &rmap_hash[i];
+		hlist_for_each_entry_safe(rmap_item, node, n, bucket, link) {
+			hlist_del(&rmap_item->link);
+			free_rmap_item(rmap_item);
+		}
+	}
+	vfree(rmap_hash);
+}
+
+static inline u32 calc_checksum(struct page *page)
+{
+	u32 checksum;
+	void *addr = kmap_atomic(page, KM_USER0);
+	checksum = jhash(addr, PAGE_SIZE, 17);
+	kunmap_atomic(addr, KM_USER0);
+	return checksum;
+}
+
+static struct rmap_item *get_rmap_item(struct mm_struct *mm, unsigned long addr)
+{
+	struct rmap_item *rmap_item;
+	struct hlist_head *bucket;
+	struct hlist_node *node;
+
+	bucket = &rmap_hash[addr % nrmaps_hash];
+	hlist_for_each_entry(rmap_item, node, bucket, link) {
+		if (mm == rmap_item->mm && rmap_item->address == addr) {
+			return rmap_item;
+		}
+	}
+	return NULL;
+}
+
+static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
+{
+	struct tree_item *tree_item;
+
+	tree_item = rmap_item->tree_item;
+	rmap_item->tree_item = NULL;
+
+	if (rmap_item->stable_tree) {
+		if (rmap_item->prev) {
+			BUG_ON(rmap_item->prev->next != rmap_item);
+			rmap_item->prev->next = rmap_item->next;
+		}
+		if (rmap_item->next) {
+			BUG_ON(rmap_item->next->prev != rmap_item);
+			rmap_item->next->prev = rmap_item->prev;
+		}
+	}
+
+	if (tree_item) {
+		if (rmap_item->stable_tree) {
+	 		if (!rmap_item->next && !rmap_item->prev) {
+				rb_erase(&tree_item->node, &root_stable_tree);
+				free_tree_item(tree_item);
+			} else if (!rmap_item->prev)
+				tree_item->rmap_item = rmap_item->next;
+			else
+				tree_item->rmap_item = rmap_item->prev;
+		} else if (!rmap_item->stable_tree)
+			free_tree_item(tree_item);
+	}
+
+	hlist_del(&rmap_item->link);
+	free_rmap_item(rmap_item);
+}
+
+static void remove_page_from_tree(struct mm_struct *mm,
+				  unsigned long addr)
+{
+	struct rmap_item *rmap_item;
+
+	rmap_item = get_rmap_item(mm, addr);
+	if (!rmap_item)
+		return;
+	remove_rmap_item_from_tree(rmap_item);
+	return;
+}
+
+static int ksm_sma_ioctl_register_memory_region(struct ksm_sma *ksm_sma,
+						struct ksm_memory_region *mem)
+{
+	struct ksm_mem_slot *slot;
+	int ret = -EPERM;
+
+	slot = kzalloc(sizeof(struct ksm_mem_slot), GFP_KERNEL);
+	if (!slot) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	slot->mm = get_task_mm(current);
+	if (!slot->mm)
+		goto out_free;
+	slot->addr = mem->addr;
+	slot->npages = mem->npages;
+
+	down_write(&slots_lock);
+
+	list_add_tail(&slot->link, &slots);
+	list_add_tail(&slot->sma_link, &ksm_sma->sma_slots);
+
+	up_write(&slots_lock);
+	return 0;
+
+out_free:
+	kfree(slot);
+out:
+	return ret;
+}
+
+static void remove_mm_from_hash_and_tree(struct mm_struct *mm)
+{
+	struct ksm_mem_slot *slot;
+	int pages_count;
+
+	list_for_each_entry(slot, &slots, link)
+		if (slot->mm == mm)
+			break;
+	BUG_ON(!slot);
+
+	root_unstable_tree = RB_ROOT;
+	for (pages_count = 0; pages_count < slot->npages; ++pages_count)
+		remove_page_from_tree(mm, slot->addr +
+				      pages_count * PAGE_SIZE);
+	list_del(&slot->link);
+}
+
+static int ksm_sma_ioctl_remove_memory_region(struct ksm_sma *ksm_sma)
+{
+	struct ksm_mem_slot *slot, *node;
+
+	down_write(&slots_lock);
+	list_for_each_entry_safe(slot, node, &ksm_sma->sma_slots, sma_link) {
+		remove_mm_from_hash_and_tree(slot->mm);
+		mmput(slot->mm);
+		list_del(&slot->sma_link);
+		kfree(slot);
+	}
+	up_write(&slots_lock);
+	return 0;
+}
+
+static int ksm_sma_release(struct inode *inode, struct file *filp)
+{
+	struct ksm_sma *ksm_sma = filp->private_data;
+	int r;
+
+	r = ksm_sma_ioctl_remove_memory_region(ksm_sma);
+	kfree(ksm_sma);
+	return r;
+}
+
+static long ksm_sma_ioctl(struct file *filp,
+			  unsigned int ioctl, unsigned long arg)
+{
+	struct ksm_sma *sma = filp->private_data;
+	void __user *argp = (void __user *)arg;
+	int r = EINVAL;
+
+	switch (ioctl) {
+	case KSM_REGISTER_MEMORY_REGION: {
+		struct ksm_memory_region ksm_memory_region;
+
+		r = -EFAULT;
+		if (copy_from_user(&ksm_memory_region, argp,
+				   sizeof(ksm_memory_region)))
+			goto out;
+		r = ksm_sma_ioctl_register_memory_region(sma,
+							 &ksm_memory_region);
+		break;
+	}
+	case KSM_REMOVE_MEMORY_REGION:
+		r = ksm_sma_ioctl_remove_memory_region(sma);
+		break;
+	}
+
+out:
+	return r;
+}
+
+static unsigned long addr_in_vma(struct vm_area_struct *vma, struct page *page)
+{
+	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+	unsigned long addr;
+
+	addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+	if (unlikely(addr < vma->vm_start || addr >= vma->vm_end))
+		return -EFAULT;
+	return addr;
+}
+
+static pte_t *get_pte(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep = NULL;
+
+	pgd = pgd_offset(mm, addr);
+	if (!pgd_present(*pgd))
+		goto out;
+
+	pud = pud_offset(pgd, addr);
+	if (!pud_present(*pud))
+		goto out;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		goto out;
+
+	ptep = pte_offset_map(pmd, addr);
+out:
+	return ptep;
+}
+
+static int is_present_pte(struct mm_struct *mm, unsigned long addr)
+{
+	pte_t *ptep;
+	int r;
+
+	ptep = get_pte(mm, addr);
+	if (!ptep)
+		return 0;
+
+	r = pte_present(*ptep);
+	pte_unmap(ptep);
+
+	return r;
+}
+
+static int memcmp_pages(struct page *page1, struct page *page2)
+{
+	char *addr1, *addr2;
+	int r;
+
+	addr1 = kmap_atomic(page1, KM_USER0);
+	addr2 = kmap_atomic(page2, KM_USER1);
+	r = memcmp(addr1, addr2, PAGE_SIZE);
+	kunmap_atomic(addr1, KM_USER0);
+	kunmap_atomic(addr2, KM_USER1);
+	return r;
+}
+
+/* pages_identical
+ * return 1 if identical, 0 otherwise.
+ */
+static inline int pages_identical(struct page *page1, struct page *page2)
+{
+	return !memcmp_pages(page1, page2);
+}
+
+/*
+ * try_to_merge_one_page - take two pages and merge them into one
+ * note:
+ * oldpage should be anon page while newpage should be file mapped page
+ *
+ * this function return 0 if the pages were merged, 1 otherwise.
+ */
+static int try_to_merge_one_page(struct mm_struct *mm,
+				 struct vm_area_struct *vma,
+				 struct page *oldpage,
+				 struct page *newpage,
+				 pgprot_t newprot)
+{
+	int ret = 1;
+	int odirect_sync;
+	unsigned long page_addr_in_vma;
+	pte_t orig_pte, *orig_ptep;
+
+	get_page(newpage);
+	get_page(oldpage);
+
+	down_read(&mm->mmap_sem);
+
+	page_addr_in_vma = addr_in_vma(vma, oldpage);
+	if (page_addr_in_vma == -EFAULT)
+		goto out_unlock;
+
+	orig_ptep = get_pte(mm, page_addr_in_vma);
+	if (!orig_ptep)
+		goto out_unlock;
+	orig_pte = *orig_ptep;
+	pte_unmap(orig_ptep);
+	if (!pte_present(orig_pte))
+		goto out_unlock;
+	if (page_to_pfn(oldpage) != pte_pfn(orig_pte))
+		goto out_unlock;
+	/*
+	 * we need the page lock to read a stable PageSwapCache in
+	 * page_wrprotect()
+	 */
+	if (TestSetPageLocked(oldpage))
+		goto out_unlock;
+	/*
+	 * page_wrprotect check if the page is swapped or in swap cache,
+	 * in the future we might want to run here if_present_pte and then
+	 * swap_free
+	 */
+	if (!page_wrprotect(oldpage, &odirect_sync, 2)) {
+		unlock_page(oldpage);
+		goto out_unlock;
+	}
+	unlock_page(oldpage);
+	if (!odirect_sync)
+		goto out_unlock;
+
+	orig_pte = pte_wrprotect(orig_pte);
+
+	if (pages_identical(oldpage, newpage))
+		ret = replace_page(vma, oldpage, newpage, orig_pte, newprot);
+
+out_unlock:
+	up_read(&mm->mmap_sem);
+	put_page(oldpage);
+	put_page(newpage);
+	return ret;
+}
+
+/*
+ * try_to_merge_two_pages - take two identical pages and prepare them to be
+ * merged into one page.
+ *
+ * this function return 0 if we successfully mapped two identical pages into one
+ * page, 1 otherwise.
+ * (note in case we created KsmPage and mapped one page into it but the second
+ *  page was not mapped we consider it as a failure and return 1)
+ */
+static int try_to_merge_two_pages(struct mm_struct *mm1, struct page *page1,
+				  struct mm_struct *mm2, struct page *page2,
+				  unsigned long addr1, unsigned long addr2)
+{
+	struct vm_area_struct *vma;
+	pgprot_t prot;
+	int ret = 1;
+
+	/*
+	 * If page2 isn't shared (it isn't PageKsm) we have to allocate a new
+	 * file mapped page and make the two ptes of mm1(page1) and mm2(page2)
+	 * point to it.  If page2 is shared, we can just make the pte of
+	 * mm1(page1) point to page2
+	 */
+	if (PageKsm(page2)) {
+		down_read(&mm1->mmap_sem);
+		vma = find_vma(mm1, addr1);
+		up_read(&mm1->mmap_sem);
+		if (!vma)
+			return ret;
+		prot = vma->vm_page_prot;
+		pgprot_val(prot) &= ~_PAGE_RW;
+		ret = try_to_merge_one_page(mm1, vma, page1, page2, prot);
+	} else {
+		struct page *kpage;
+
+		kpage = alloc_page(GFP_HIGHUSER);
+		if (!kpage)
+			return ret;
+		down_read(&mm1->mmap_sem);
+		vma = find_vma(mm1, addr1);
+		up_read(&mm1->mmap_sem);
+		if (!vma) {
+			put_page(kpage);
+			return ret;
+		}
+		prot = vma->vm_page_prot;
+		pgprot_val(prot) &= ~_PAGE_RW;
+
+		copy_user_highpage(kpage, page1, addr1);
+		ret = try_to_merge_one_page(mm1, vma, page1, kpage, prot);
+
+		if (!ret) {
+			down_read(&mm2->mmap_sem);
+			vma = find_vma(mm2, addr2);
+			up_read(&mm2->mmap_sem);
+			if (!vma) {
+				put_page(kpage);
+				ret = 1;
+				return ret;
+			}
+
+			prot = vma->vm_page_prot;
+			pgprot_val(prot) &= ~_PAGE_RW;
+
+			ret = try_to_merge_one_page(mm2, vma, page2, kpage,
+						    prot);
+			/*
+			 * If the secoend try_to_merge_one_page call was failed,
+			 * we are in situation where we have Ksm page that have
+			 * just one pte pointing to it, in this case we break
+			 * it.
+			 */
+			if (ret) {
+				struct page *tmppage[1];
+
+				down_read(&mm1->mmap_sem);
+				if (get_user_pages(current, mm1, addr1, 1, 1,
+						    0, tmppage, NULL)) {
+					put_page(tmppage[0]);
+				}
+				up_read(&mm1->mmap_sem);
+			}
+		}
+		put_page(kpage);
+	}
+	return ret;
+}
+
+static int is_zapped_item(struct rmap_item *rmap_item,
+			  struct page **page)
+{
+	int ret = 0;
+
+	cond_resched();
+	if (is_present_pte(rmap_item->mm, rmap_item->address)) {
+		down_read(&rmap_item->mm->mmap_sem);
+		ret = get_user_pages(current, rmap_item->mm, rmap_item->address,
+				     1, 0, 0, page, NULL);
+		up_read(&rmap_item->mm->mmap_sem);
+	}
+
+	if (!ret)
+		return 1;
+
+	if (unlikely(!PageKsm(page[0]))) {
+		put_page(page[0]);
+		return 1;
+	}
+	return 0;
+}
+
+static struct rmap_item *stable_tree_search(struct page *page,
+					    struct page **page2,
+					    struct rmap_item *rmap_item)
+{
+	struct rb_node *node = root_stable_tree.rb_node;
+	struct tree_item *tree_item;
+	struct rmap_item *found_rmap_item;
+
+	while (node) {
+		int ret;
+
+		tree_item = rb_entry(node, struct tree_item, node);
+		found_rmap_item = tree_item->rmap_item;
+		while (found_rmap_item) {
+			BUG_ON(!found_rmap_item->stable_tree);
+			BUG_ON(!found_rmap_item->tree_item);
+			if (!rmap_item ||
+			     !(found_rmap_item->mm == rmap_item->mm &&
+			      found_rmap_item->address == rmap_item->address)) {
+				if (!is_zapped_item(found_rmap_item, page2))
+					break;
+				remove_rmap_item_from_tree(found_rmap_item);
+			}
+			found_rmap_item = found_rmap_item->next;
+		}
+		if (!found_rmap_item)
+			goto out_didnt_find;
+
+		/*
+		 * We can trust the value of the memcmp as we know the pages
+		 * are write protected.
+		 */
+		ret = memcmp_pages(page, page2[0]);
+
+		if (ret < 0) {
+			put_page(page2[0]);
+			node = node->rb_left;
+		}
+		else if (ret > 0) {
+			put_page(page2[0]);
+			node = node->rb_right;
+		}
+		else
+			goto out_found;
+	}
+out_didnt_find:
+	found_rmap_item = NULL;
+out_found:
+	return found_rmap_item;
+}
+
+static int stable_tree_insert(struct page *page,
+			      struct tree_item *new_tree_item,
+			      struct rmap_item *rmap_item)
+{
+	struct rb_node **new = &(root_stable_tree.rb_node);
+	struct rb_node *parent = NULL;
+	struct tree_item *tree_item;
+	struct page *page2[1];
+
+	while (*new) {
+		int ret;
+		struct rmap_item *insert_rmap_item;
+
+		tree_item = rb_entry(*new, struct tree_item, node);
+		BUG_ON(!tree_item);
+		BUG_ON(!tree_item->rmap_item);
+
+		insert_rmap_item = tree_item->rmap_item;
+		while (insert_rmap_item) {
+			BUG_ON(!insert_rmap_item->stable_tree);
+			BUG_ON(!insert_rmap_item->tree_item);
+			if (!rmap_item ||
+			    !(insert_rmap_item->mm == rmap_item->mm &&
+			     insert_rmap_item->address == rmap_item->address)) {
+				if (!is_zapped_item(insert_rmap_item, page2))
+					break;
+				remove_rmap_item_from_tree(insert_rmap_item);
+			}
+			insert_rmap_item = insert_rmap_item->next;
+		}
+		if (!insert_rmap_item)
+			return 1;
+
+		ret = memcmp_pages(page, page2[0]);
+
+		parent = *new;
+		if (ret < 0) {
+			put_page(page2[0]);
+			new = &((*new)->rb_left);
+		}
+		else if (ret > 0) {
+			put_page(page2[0]);
+			new = &((*new)->rb_right);
+		}
+		else {
+			/*
+			 * It isnt a bug when we are here,
+			 * beacuse after we release the stable_tree_lock
+			 * someone else could have merge identical page to the
+			 * tree.
+			 */
+			return 1;
+		}
+	}
+
+	rb_link_node(&new_tree_item->node, parent, new);
+	rb_insert_color(&new_tree_item->node, &root_stable_tree);
+	rmap_item->stable_tree = 1;
+	rmap_item->tree_item = new_tree_item;
+
+	return 0;
+}
+
+static struct tree_item *unstable_tree_search_insert(struct page *page,
+					struct page **page2,
+					struct rmap_item *page_rmap_item)
+{
+	struct rb_node **new = &(root_unstable_tree.rb_node);
+	struct rb_node *parent = NULL;
+	struct tree_item *tree_item;
+	struct tree_item *new_tree_item;
+	struct rmap_item *rmap_item;
+	unsigned int checksum;
+
+	while (*new) {
+		int ret;
+
+		tree_item = rb_entry(*new, struct tree_item, node);
+		BUG_ON(!tree_item);
+		rmap_item = tree_item->rmap_item;
+		BUG_ON(!rmap_item);
+
+		/*
+		 * We dont want to swap in pages
+		 */
+		if (!is_present_pte(rmap_item->mm, rmap_item->address))
+			return NULL;
+
+		down_read(&rmap_item->mm->mmap_sem);
+		ret = get_user_pages(current, rmap_item->mm, rmap_item->address,
+				     1, 0, 0, page2, NULL);
+		up_read(&rmap_item->mm->mmap_sem);
+		if (!ret)
+			return NULL;
+
+		ret = memcmp_pages(page, page2[0]);
+
+		parent = *new;
+		if (ret < 0) {
+			put_page(page2[0]);
+			new = &((*new)->rb_left);
+		}
+		else if (ret > 0) {
+			put_page(page2[0]);
+			new = &((*new)->rb_right);
+		} else
+			return tree_item;
+	}
+
+	if (!page_rmap_item)
+		return NULL;
+
+	checksum = calc_checksum(page);
+	if (page_rmap_item->oldchecksum != checksum) {
+		page_rmap_item->oldchecksum = checksum;
+		return NULL;
+	}
+
+	new_tree_item = alloc_tree_item();
+	if (!new_tree_item)
+		return NULL;
+
+	page_rmap_item->tree_item = new_tree_item;
+	page_rmap_item->stable_tree = 0;
+	new_tree_item->rmap_item = page_rmap_item;
+	rb_link_node(&new_tree_item->node, parent, new);
+	rb_insert_color(&new_tree_item->node, &root_unstable_tree);
+
+	return NULL;
+}
+
+/*
+ * update_stable_tree - check if the page inside the tree got zapped,
+ * and if it got zapped, kick it from the tree.
+ */
+int update_tree(struct rmap_item *rmap_item, int *wait)
+{
+	struct page *page[1];
+
+	if (!rmap_item->stable_tree) {
+		if (rmap_item->tree_item) {
+			remove_rmap_item_from_tree(rmap_item);
+			return 1;
+		}
+		return 0;
+	}
+	if (is_zapped_item(rmap_item, page)) {
+		remove_rmap_item_from_tree(rmap_item);
+		*wait = 1;
+		return 1;
+	}
+	put_page(page[0]);
+	return 0;
+}
+
+static struct rmap_item *create_new_rmap_item(struct mm_struct *mm,
+			 		      unsigned long addr,
+					      unsigned int checksum)
+{
+	struct rmap_item *rmap_item;
+	struct hlist_head *bucket;
+
+	rmap_item = alloc_rmap_item();
+	if (!rmap_item)
+		return NULL;
+
+	rmap_item->mm = mm;
+	rmap_item->address = addr;
+	rmap_item->oldchecksum = checksum;
+	rmap_item->stable_tree = 0;
+	rmap_item->tree_item = NULL;
+
+	bucket = &rmap_hash[addr % nrmaps_hash];
+	hlist_add_head(&rmap_item->link, bucket);
+
+	return rmap_item;
+}
+
+/*
+ * cmp_and_merge_page - take a page computes its hash value and check if there
+ * is similar hash value to different page,
+ * in case we find that there is similar hash to different page we call to
+ * try_to_merge_two_pages().
+ */
+static int cmp_and_merge_page(struct ksm_scan *ksm_scan, struct page *page)
+{
+	struct page *page2[1];
+	struct ksm_mem_slot *slot;
+	struct tree_item *tree_item;
+	struct rmap_item *rmap_item;
+	struct rmap_item *tree_rmap_item;
+	unsigned int checksum;
+	unsigned long addr;
+	int wait = 0;
+
+	slot = ksm_scan->slot_index;
+	addr = slot->addr + ksm_scan->page_index * PAGE_SIZE;
+	rmap_item = get_rmap_item(slot->mm, addr);
+	if (rmap_item) {
+		if (update_tree(rmap_item, &wait))
+			rmap_item = NULL;
+	}
+
+	tree_rmap_item = stable_tree_search(page, page2, rmap_item);
+	if (tree_rmap_item) {
+		int ret;
+
+		BUG_ON(!tree_rmap_item->tree_item);
+		ret = try_to_merge_two_pages(slot->mm, page, tree_rmap_item->mm,
+					     page2[0], addr,
+					     tree_rmap_item->address);
+		put_page(page2[0]);
+		if (!ret) {
+			if (!rmap_item)
+				rmap_item = create_new_rmap_item(slot->mm,
+								 addr, 0);
+			if (!rmap_item)
+				return !ret;
+
+
+			rmap_item->next = tree_rmap_item->next;
+			rmap_item->prev = tree_rmap_item;
+
+			if (tree_rmap_item->next)
+				tree_rmap_item->next->prev = rmap_item;
+
+			tree_rmap_item->next = rmap_item;
+
+			rmap_item->stable_tree = 1;
+			rmap_item->tree_item = tree_rmap_item->tree_item;
+		}
+		return !ret;
+	}
+
+	tree_item = unstable_tree_search_insert(page, page2, rmap_item);
+	if (tree_item) {
+		int ret;
+
+		rmap_item = tree_item->rmap_item;
+		BUG_ON(!rmap_item);
+		ret = try_to_merge_two_pages(slot->mm, page, rmap_item->mm,
+					     page2[0], addr,
+					     rmap_item->address);
+		if (!ret) {
+			rb_erase(&tree_item->node, &root_unstable_tree);
+			stable_tree_insert(page2[0], tree_item, rmap_item);
+		}
+		put_page(page2[0]);
+		return !ret;
+	}
+	if (!wait && !rmap_item) {
+		checksum = calc_checksum(page);
+		create_new_rmap_item(slot->mm, addr, checksum);
+		return 0;
+	}
+	return 0;
+}
+
+/* return -EAGAIN - no slots registered, nothing to be done */
+static int scan_get_next_index(struct ksm_scan *ksm_scan, int nscan)
+{
+	struct ksm_mem_slot *slot;
+
+	if (list_empty(&slots))
+		return -EAGAIN;
+
+	slot = ksm_scan->slot_index;
+
+	/* Are there pages left in this slot to scan? */
+	if ((slot->npages - ksm_scan->page_index - nscan) > 0) {
+		ksm_scan->page_index += nscan;
+		return 0;
+	}
+
+	list_for_each_entry_from(slot, &slots, link) {
+		if (slot == ksm_scan->slot_index)
+			continue;
+		ksm_scan->page_index = 0;
+		ksm_scan->slot_index = slot;
+		return 0;
+	}
+
+	/* look like we finished scanning the whole memory, starting again */
+	root_unstable_tree = RB_ROOT;
+	ksm_scan->page_index = 0;
+	ksm_scan->slot_index = list_first_entry(&slots,
+						struct ksm_mem_slot, link);
+	return 0;
+}
+
+/*
+ * update slot_index - make sure ksm_scan will point to vaild data,
+ * it is possible that by the time we are here the data that ksm_scan was
+ * pointed to was released so we have to call this function every time after
+ * taking the slots_lock
+ */
+static void scan_update_old_index(struct ksm_scan *ksm_scan)
+{
+	struct ksm_mem_slot *slot;
+
+	if (list_empty(&slots))
+		return;
+
+	list_for_each_entry(slot, &slots, link) {
+		if (ksm_scan->slot_index == slot)
+			return;
+	}
+
+	ksm_scan->slot_index = list_first_entry(&slots,
+						struct ksm_mem_slot, link);
+	ksm_scan->page_index = 0;
+}
+
+/**
+ * ksm_scan_start - the ksm scanner main worker function.
+ * @ksm_scan -    the scanner.
+ * @scan_npages - number of pages we are want to scan before we return from this
+ * @function.
+ *
+ * (this function can be called from the kernel thread scanner, or from 
+ *  userspace ioctl context scanner)
+ *
+ *  The function return -EAGAIN in case there are not slots to scan.
+ */
+static int ksm_scan_start(struct ksm_scan *ksm_scan, int scan_npages)
+{
+	struct ksm_mem_slot *slot;
+	struct page *page[1];
+	int val;
+	int ret = 0;
+
+	down_read(&slots_lock);
+
+	scan_update_old_index(ksm_scan);
+
+	while (scan_npages > 0) {
+		ret = scan_get_next_index(ksm_scan, 1);
+		if (ret)
+			goto out;
+
+		slot = ksm_scan->slot_index;
+
+		cond_resched();
+
+		/*
+		 * If the page is swapped out or in swap cache, we don't want to
+		 * scan it (it is just for performance).
+		 */
+		if (is_present_pte(slot->mm, slot->addr +
+				   ksm_scan->page_index * PAGE_SIZE)) {
+			down_read(&slot->mm->mmap_sem);
+			val = get_user_pages(current, slot->mm, slot->addr +
+					     ksm_scan->page_index * PAGE_SIZE ,
+					      1, 0, 0, page, NULL);
+			up_read(&slot->mm->mmap_sem);
+			if (val == 1) {
+				if (!PageKsm(page[0]))
+					cmp_and_merge_page(ksm_scan, page[0]);
+				put_page(page[0]);
+			}
+		}
+		scan_npages--;
+	}
+	scan_get_next_index(ksm_scan, 1);
+out:
+	up_read(&slots_lock);
+	return ret;
+}
+
+/*
+ * no multithreaded ksm for ovirt
+ */
+/*static int ksm_scan_ioctl_start(struct ksm_scan *ksm_scan,
+				struct ksm_user_scan *scan)
+{
+	if (!(scan->flags & ksm_control_flags_run))
+		return 0;
+
+	return ksm_scan_start(ksm_scan, scan->pages_to_scan);
+}*/
+
+static int ksm_scan_release(struct inode *inode, struct file *filp)
+{
+	struct ksm_scan *ksm_scan = filp->private_data;
+
+	kfree(ksm_scan);
+	return 0;
+}
+
+static long ksm_scan_ioctl(struct file *filp,
+			   unsigned int ioctl, unsigned long arg)
+{
+//	struct ksm_scan *ksm_scan = filp->private_data;
+	//void __user *argp = (void __user *)arg;
+	int r = EINVAL;
+
+	switch (ioctl) {
+	/*
+	 * i didnt implemented the locking yet, and in ovirt we dont run
+	 * multi-threaded ksm.
+	 */
+	/*case KSM_SCAN: {
+		struct ksm_user_scan scan;
+
+		r = -EFAULT;
+		if (copy_from_user(&scan, argp,
+				   sizeof(struct ksm_user_scan)))
+			break;
+
+		r = ksm_scan_ioctl_start(ksm_scan, &scan);
+	}*/
+	}
+	return r;
+}
+
+static struct file_operations ksm_sma_fops = {
+	.release        = ksm_sma_release,
+	.unlocked_ioctl = ksm_sma_ioctl,
+	.compat_ioctl   = ksm_sma_ioctl,
+};
+
+static int ksm_dev_ioctl_create_shared_memory_area(void)
+{
+	int fd = -1;
+	struct ksm_sma *ksm_sma;
+
+	ksm_sma = kmalloc(sizeof(struct ksm_sma), GFP_KERNEL);
+	if (!ksm_sma)
+		goto out;
+
+	INIT_LIST_HEAD(&ksm_sma->sma_slots);
+
+	fd = anon_inode_getfd("ksm-sma", &ksm_sma_fops, ksm_sma, 0);
+	if (fd < 0)
+		goto out_free;
+
+	return fd;
+out_free:
+	kfree(ksm_sma);
+out:
+	return fd;
+}
+
+static struct file_operations ksm_scan_fops = {
+	.release        = ksm_scan_release,
+	.unlocked_ioctl = ksm_scan_ioctl,
+	.compat_ioctl   = ksm_scan_ioctl,
+};
+
+static struct ksm_scan *ksm_scan_create(void)
+{
+	return kzalloc(sizeof(struct ksm_scan), GFP_KERNEL);
+}
+
+static int ksm_dev_ioctl_create_scan(void)
+{
+	int fd = -ENOMEM;
+	struct ksm_scan *ksm_scan;
+
+	ksm_scan = ksm_scan_create();
+	if (!ksm_scan)
+		goto out;
+
+	fd = anon_inode_getfd("ksm-scan", &ksm_scan_fops, ksm_scan, 0);
+	if (fd < 0)
+		goto out_free;
+	return fd;
+
+out_free:
+	kfree(ksm_scan);
+out:
+	return fd;
+}
+
+/*
+ * ksm_dev_ioctl_start_stop_kthread - control the kernel thread scanning running
+ * speed.
+ * This function allow us to control on the time the kernel thread will sleep
+ * how many pages it will scan between sleep and sleep, and how many pages it
+ * will maximum merge between sleep and sleep.
+ */
+static int ksm_dev_ioctl_start_stop_kthread(struct ksm_kthread_info *info)
+{
+	int rc = 0;
+
+	down_write(&kthread_lock);
+
+	if (info->flags & ksm_control_flags_run) {
+		if (!info->pages_to_scan) {
+			rc = EPERM;
+			up_write(&kthread_lock);
+			goto out;
+		}
+	}
+
+	kthread_sleep = info->sleep;
+	kthread_pages_to_scan = info->pages_to_scan;
+	ksmd_flags = info->flags;
+
+	up_write(&kthread_lock);
+
+	if (ksmd_flags & ksm_control_flags_run)
+		wake_up_interruptible(&kthread_wait);
+
+out:
+	return rc;
+}
+
+/*
+ * ksm_dev_ioctl_get_info_kthread - write into info the scanning information
+ * of the ksm kernel thread
+ */
+static void ksm_dev_ioctl_get_info_kthread(struct ksm_kthread_info *info)
+{
+	down_read(&kthread_lock);
+
+	info->sleep = kthread_sleep;
+	info->pages_to_scan = kthread_pages_to_scan;
+	info->flags = ksmd_flags;
+
+	up_read(&kthread_lock);
+}
+
+static long ksm_dev_ioctl(struct file *filp,
+			  unsigned int ioctl, unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	long r = -EINVAL;
+
+	switch (ioctl) {
+	case KSM_GET_API_VERSION:
+		r = KSM_API_VERSION;
+		break;
+	case KSM_CREATE_SHARED_MEMORY_AREA:
+		r = ksm_dev_ioctl_create_shared_memory_area();
+		break;
+	case KSM_CREATE_SCAN:
+		r = ksm_dev_ioctl_create_scan();
+		break;
+	case KSM_START_STOP_KTHREAD: {
+		struct ksm_kthread_info info;
+
+		r = -EFAULT;
+		if (copy_from_user(&info, argp,
+				   sizeof(struct ksm_kthread_info)))
+			break;
+
+		r = ksm_dev_ioctl_start_stop_kthread(&info);
+		break;
+		}
+	case KSM_GET_INFO_KTHREAD: {
+		struct ksm_kthread_info info;
+
+		ksm_dev_ioctl_get_info_kthread(&info);
+		r = -EFAULT;
+		if (copy_to_user(argp, &info,
+				 sizeof(struct ksm_kthread_info)))
+			break;
+		r = 0;
+		break;
+	}
+	default:
+		break;
+	}
+	return r;
+}
+
+static struct file_operations ksm_chardev_ops = {
+	.unlocked_ioctl = ksm_dev_ioctl,
+	.compat_ioctl   = ksm_dev_ioctl,
+	.owner          = THIS_MODULE,
+};
+
+static struct miscdevice ksm_dev = {
+	KSM_MINOR,
+	"ksm",
+	&ksm_chardev_ops,
+};
+
+int kthread_ksm_scan_thread(void *nothing)
+{
+	while (!kthread_should_stop()) {
+		if (ksmd_flags & ksm_control_flags_run) {
+			down_read(&kthread_lock);
+			ksm_scan_start(&kthread_ksm_scan,
+				       kthread_pages_to_scan);
+			up_read(&kthread_lock);
+			schedule_timeout_interruptible(
+					usecs_to_jiffies(kthread_sleep));
+		} else
+			wait_event_interruptible(kthread_wait,
+					ksmd_flags & ksm_control_flags_run ||
+					kthread_should_stop());
+	}
+	return 0;
+}
+
+static int __init ksm_init(void)
+{
+	int r;
+
+	r = ksm_slab_init();
+	if (r)
+		goto out;
+
+	r = rmap_hash_init();
+	if (r)
+		goto out_free1;
+
+	kthread = kthread_run(kthread_ksm_scan_thread, NULL, "kksmd");
+	if (IS_ERR(kthread)) {
+		printk(KERN_ERR "ksm: creating kthread failed\n");
+		r = PTR_ERR(kthread);
+		goto out_free2;
+	}
+
+	r = init_wp_notifier();
+	if (r)
+		goto out_free3;
+
+	r = misc_register(&ksm_dev);
+	if (r) {
+		printk(KERN_ERR "ksm: misc device register failed\n");
+		goto out_free4;
+	}
+
+	printk(KERN_WARNING "ksm loaded\n");
+	return 0;
+
+out_free4:
+	exit_wp_notifier();
+out_free3:
+	kthread_stop(kthread);
+out_free2:
+	rmap_hash_free();
+out_free1:
+	ksm_slab_free();
+out:
+	return r;
+}
+
+static void __exit ksm_exit(void)
+{
+	misc_deregister(&ksm_dev);
+	exit_wp_notifier();
+	ksmd_flags = ksm_control_flags_run;
+	kthread_stop(kthread);
+	rmap_hash_free();
+	ksm_slab_free();
+}
+
+module_init(ksm_init)
+module_exit(ksm_exit)
diff --git a/kernel/ksm/ksm.h b/kernel/ksm/ksm.h
new file mode 100644
index 0000000..91ca286
--- /dev/null
+++ b/kernel/ksm/ksm.h
@@ -0,0 +1,84 @@
+#ifndef __LINUX_KSM_H
+#define __LINUX_KSM_H
+
+/*
+ * Userspace interface for /dev/ksm - kvm shared memory
+ */
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+#include <linux/ioctl.h>
+#else
+#include <sys/types.h>
+#include <sys/ioctl.h>
+#endif
+
+#include <asm/types.h>
+
+#define KSM_API_VERSION 1
+
+#define ksm_control_flags_run 1
+
+/* for KSM_REGISTER_MEMORY_REGION */
+struct ksm_memory_region {
+	__u32 npages; /* number of pages to share */
+	__u32 pad;
+	__u64 addr; /* the begining of the virtual address */
+};
+
+struct ksm_user_scan {
+	__u32 pages_to_scan;
+	__u32 flags; /* control flags */
+};
+
+struct ksm_kthread_info {
+	__u32 sleep; /* number of microsecoends to sleep */
+	__u32 pages_to_scan; /* number of pages to scan */
+	__u32 flags; /* control flags */
+};
+
+#define KSMIO 0xAB
+
+/* ioctls for /dev/ksm */
+
+#define KSM_GET_API_VERSION              _IO(KSMIO,   0x00)
+/*
+ * KSM_CREATE_SHARED_MEMORY_AREA - create the shared memory reagion fd
+ */
+#define KSM_CREATE_SHARED_MEMORY_AREA    _IO(KSMIO,   0x01) /* return SMA fd */
+/*
+ * KSM_CREATE_SCAN - create the scanner fd
+ */
+#define KSM_CREATE_SCAN                  _IO(KSMIO,   0x02) /* return SCAN fd */
+/*
+ * KSM_START_STOP_KTHREAD - control the kernel thread scanning speed
+ * (can stop the kernel thread from working by setting running = 0)
+ */
+#define KSM_START_STOP_KTHREAD		 _IOW(KSMIO,  0x03,\
+					      struct ksm_kthread_info)
+/*
+ * KSM_GET_INFO_KTHREAD - return information about the kernel thread
+ * scanning speed.
+ */
+#define KSM_GET_INFO_KTHREAD		 _IOW(KSMIO,  0x04,\
+					      struct ksm_kthread_info)
+
+
+/* ioctls for SMA fds */
+
+/*
+ * KSM_REGISTER_MEMORY_REGION - register virtual address memory area to be
+ * scanned by kvm.
+ */
+#define KSM_REGISTER_MEMORY_REGION       _IOW(KSMIO,  0x20,\
+					      struct ksm_memory_region)
+/*
+ * KSM_REMOVE_MEMORY_REGION - remove virtual address memory area from ksm.
+ */
+#define KSM_REMOVE_MEMORY_REGION         _IO(KSMIO,   0x21)
+
+/* ioctls for SCAN fds */
+#define KSM_SCAN                         _IOW(KSMIO,  0x40,\
+					      struct ksm_user_scan)
+
+#endif
diff --git a/kernel/ksm/wp_notifier.c b/kernel/ksm/wp_notifier.c
new file mode 100644
index 0000000..0da4499
--- /dev/null
+++ b/kernel/ksm/wp_notifier.c
@@ -0,0 +1,60 @@
+#include <linux/version.h>
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/kallsyms.h>
+#include "wp_notifier.h"
+
+static int pre_do_wp_page(struct kprobe *p,
+                         struct pt_regs *regs)
+{
+       struct mm_struct *mm;
+       unsigned long address;
+
+       /*
+        * kprobes runs with irq disabled and preempt disabled but we
+        * need irq enabled to flush the smp tlb with IPIs while
+        * tearing down sptes.
+        */
+       local_irq_enable();
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,25)
+       mm = (struct mm_struct *) regs->rdi;
+       address = (unsigned long) regs->rdx;
+#else
+       mm = (struct mm_struct *) regs->di;
+       address = (unsigned long) regs->dx;
+#endif
+       kvm_wp_notifier(mm, address);
+
+       local_irq_disable();
+
+       return 0;
+}
+
+static struct kprobe not_kprobe;
+
+int init_wp_notifier(void)
+{
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18) && defined(CONFIG_KALLSYMS) && !defined(RHEL_RELEASE_CODE)
+       not_kprobe.addr = (kprobe_opcode_t *)kallsyms_lookup_name("do_wp_page");
+       if (!not_kprobe.addr) {
+               printk(KERN_WARNING "do_wp_page not found");
+               return 1;
+       }
+#else
+       not_kprobe.symbol_name = "do_wp_page";
+#endif
+       not_kprobe.pre_handler = pre_do_wp_page;
+
+       if (register_kprobe(&not_kprobe)) {
+               printk(KERN_WARNING "cant register kprobe for do_wp_page");
+               return 1;
+       }
+
+       return 0;
+}
+
+void exit_wp_notifier(void)
+{
+       unregister_kprobe(&not_kprobe);
+}
diff --git a/kernel/ksm/wp_notifier.h b/kernel/ksm/wp_notifier.h
new file mode 100644
index 0000000..3788e8c
--- /dev/null
+++ b/kernel/ksm/wp_notifier.h
@@ -0,0 +1,12 @@
+#ifndef WP_NOTIFIER_H
+#define WP_NOTIFIER_H
+
+#include <linux/mm.h>
+
+int init_wp_notifier(void);
+void exit_wp_notifier(void);
+
+void kvm_wp_notifier(struct mm_struct *mm,
+                    unsigned long address);
+
+#endif
-- 
1.6.1