[RFC v14][PATCH 09/54] Restore memory address space

[Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>]

Restoring the memory address space begins with nuking the existing one
of the current process, and then reading the VMA state and contents.
Call do_mmap_pgoffset() for each VMA and then read in the data.

Currently to restore private mapped memory we use the pathname saved
to open a new file and pass it to do_mmap_pgoff(). Later we change
that to reference a file object.

Changelog[v14]:
  - Introduce per vma-type restore() function
  - Merge restart code into same file as checkpoint (memory.c)
  - Compare saved 'vdso' field of mm_context with current value
  - Check whether calls to ckpt_hbuf_get() fail
  - Discard field 'h->parent'
  - Revert change to pr_debug(), back to ckpt_debug()

Changelog[v13]:
  - Avoid access to hh->vma_type after the header is freed
  - Test for no vma's in exit_mmap() before calling unmap_vma() (or it
    may crash if restart fails after having removed all vma's)

Changelog[v12]:
  - Replace obsolete ckpt_debug() with pr_debug()

Changelog[v9]:
  - Introduce ckpt_ctx_checkpoint() for checkpoint-specific ctx setup

Changelog[v7]:
  - Fix argument given to kunmap_atomic() in memory dump/restore

Changelog[v6]:
  - Balance all calls to ckpt_hbuf_get() with matching ckpt_hbuf_put()
    (even though it's not really needed)

Changelog[v5]:
  - Improve memory restore code (following Dave Hansen's comments)
  - Change dump format (and code) to allow chunks of <vaddrs, pages>
    instead of one long list of each
  - Memory restore now maps user pages explicitly to copy data into them,
    instead of reading directly to user space; got rid of mprotect_fixup()

Changelog[v4]:
  - Use standard list_... for ckpt_pgarr


Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 arch/x86/include/asm/checkpoint_hdr.h |    5 +
 arch/x86/mm/checkpoint.c              |   59 +++++
 checkpoint/checkpoint_arch.h          |    1 +
 checkpoint/files.c                    |   33 +++
 checkpoint/memory.c                   |  407 +++++++++++++++++++++++++++++++++
 checkpoint/process.c                  |    4 +
 checkpoint/restart.c                  |    9 +
 include/linux/checkpoint.h            |    5 +
 include/linux/checkpoint_hdr.h        |    6 +-
 include/linux/mm.h                    |    9 +
 mm/filemap.c                          |   18 ++
 mm/mmap.c                             |   30 ++-
 12 files changed, 580 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h
index bad7b29..d61653c 100644
--- a/arch/x86/include/asm/checkpoint_hdr.h
+++ b/arch/x86/include/asm/checkpoint_hdr.h
@@ -104,4 +104,9 @@ struct ckpt_hdr_mm_context {
 	__u32 nldt;
 } __attribute__((aligned(8)));
 
+#ifdef __KERNEL__
+/* misc prototypes from kernel (not defined elsewhere) */
+asmlinkage int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount);
+#endif
+
 #endif /* __ASM_X86_CKPT_HDR__H */
diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
index ede7045..a475a30 100644
--- a/arch/x86/mm/checkpoint.c
+++ b/arch/x86/mm/checkpoint.c
@@ -13,6 +13,7 @@
 
 #include <asm/desc.h>
 #include <asm/i387.h>
+#include <asm/elf.h>
 
 #include <linux/checkpoint_types.h>
 #include <asm/checkpoint_hdr.h>
@@ -475,3 +476,61 @@ int restore_read_header_arch(struct ckpt_ctx *ctx)
 	ckpt_hdr_put(ctx, h);
 	return ret;
 }
+
+int restore_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
+{
+	struct ckpt_hdr_mm_context *h;
+	unsigned int n;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_MM_CONTEXT);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ckpt_debug("nldt %d vdso %#lx (%p)\n",
+		 h->nldt, (unsigned long) h->vdso, mm->context.vdso);
+
+	ret = -EINVAL;
+	if (h->vdso != (unsigned long) mm->context.vdso)
+		goto out;
+	if (h->ldt_entry_size != LDT_ENTRY_SIZE)
+		goto out;
+
+	/*
+	 * to utilize the syscall modify_ldt() we first convert the data
+	 * in the checkpoint image from 'struct desc_struct' to 'struct
+	 * user_desc' with reverse logic of include/asm/desc.h:fill_ldt()
+	 */
+	ret = 0;
+	for (n = 0; n < h->nldt; n++) {
+		struct user_desc info;
+		struct desc_struct desc;
+		mm_segment_t old_fs;
+
+		ret = ckpt_kread(ctx, &desc, LDT_ENTRY_SIZE);
+		if (ret < 0)
+			break;
+
+		info.entry_number = n;
+		info.base_addr = desc.base0 | (desc.base1 << 16);
+		info.limit = desc.limit0;
+		info.seg_32bit = desc.d;
+		info.contents = desc.type >> 2;
+		info.read_exec_only = (desc.type >> 1) ^ 1;
+		info.limit_in_pages = desc.g;
+		info.seg_not_present = desc.p ^ 1;
+		info.useable = desc.avl;
+
+		old_fs = get_fs();
+		set_fs(get_ds());
+		ret = sys_modify_ldt(1, (struct user_desc __user *) &info,
+				     sizeof(info));
+		set_fs(old_fs);
+
+		if (ret < 0)
+			break;
+	}
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
diff --git a/checkpoint/checkpoint_arch.h b/checkpoint/checkpoint_arch.h
index d168b9c..4b9b6bf 100644
--- a/checkpoint/checkpoint_arch.h
+++ b/checkpoint/checkpoint_arch.h
@@ -8,3 +8,4 @@ extern int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm);
 extern int restore_read_header_arch(struct ckpt_ctx *ctx);
 extern int restore_thread(struct ckpt_ctx *ctx);
 extern int restore_cpu(struct ckpt_ctx *ctx);
+extern int restore_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm);
diff --git a/checkpoint/files.c b/checkpoint/files.c
index 1718526..a7cf6c3 100644
--- a/checkpoint/files.c
+++ b/checkpoint/files.c
@@ -86,3 +86,36 @@ int checkpoint_file(struct ckpt_ctx *ctx, struct file *file)
 {
 	return dump_fname(ctx, &file->f_path, &ctx->fs_mnt);
 }
+
+/**************************************************************************
+ * Restart
+ */
+
+/**
+ * read_open_fname - read a file name and open a file
+ * @ctx: checkpoint context
+ * @flags: file flags
+ * @mode: file mode
+ */
+static struct file *read_open_fname(struct ckpt_ctx *ctx, int flags, int mode)
+{
+	struct ckpt_hdr *h;
+	struct file *file;
+	char *fname;
+
+	h = ckpt_read_buf_type(ctx, PATH_MAX, CKPT_HDR_FNAME);
+	if (IS_ERR(h))
+		return (struct file *) h;
+	fname = (char *) (h + 1);
+	ckpt_debug("fname '%s' flags %#x mode %#x\n", fname, flags, mode);
+
+	file = filp_open(fname, flags, mode);
+	ckpt_hdr_put(ctx, h);
+	return file;
+}
+
+struct file *restore_file(struct ckpt_ctx *ctx)
+{
+	/* currently only called for mapped files; O_RDONLY works */
+	return read_open_fname(ctx, O_RDONLY, 0);
+}
diff --git a/checkpoint/memory.c b/checkpoint/memory.c
index 668d883..c725519 100644
--- a/checkpoint/memory.c
+++ b/checkpoint/memory.c
@@ -15,6 +15,9 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/file.h>
+#include <linux/err.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
 #include <linux/pagemap.h>
 #include <linux/mm_types.h>
 #include <linux/checkpoint.h>
@@ -598,3 +601,407 @@ int checkpoint_mm(struct ckpt_ctx *ctx, struct task_struct *t)
 	mmput(mm);
 	return ret;
 }
+
+/*
+ * Restart
+ *
+ * Unlike checkpoint, restart is executed in the context of each restarting
+ * process: vma regions are restored via a call to mmap(), and the data is
+ * read into the address space of the current process.
+ */
+
+/**
+ * read_pages_vaddrs - read addresses of pages to page-array chain
+ * @ctx - restart context
+ * @nr_pages - number of address to read
+ */
+static int read_pages_vaddrs(struct ckpt_ctx *ctx, unsigned long nr_pages)
+{
+	struct ckpt_pgarr *pgarr;
+	unsigned long *vaddrp;
+	int nr, ret;
+
+	while (nr_pages) {
+		pgarr = pgarr_current(ctx);
+		if (!pgarr)
+			return -ENOMEM;
+		nr = pgarr_nr_free(pgarr);
+		if (nr > nr_pages)
+			nr = nr_pages;
+		vaddrp = &pgarr->vaddrs[pgarr->nr_used];
+		ret = ckpt_kread(ctx, vaddrp, nr * sizeof(unsigned long));
+		if (ret < 0)
+			return ret;
+		pgarr->nr_used += nr;
+		nr_pages -= nr;
+	}
+	return 0;
+}
+
+static int restore_read_page(struct ckpt_ctx *ctx, struct page *page, void *p)
+{
+	void *ptr;
+	int ret;
+
+	ret = ckpt_kread(ctx, p, PAGE_SIZE);
+	if (ret < 0)
+		return ret;
+
+	ptr = kmap_atomic(page, KM_USER1);
+	memcpy(ptr, p, PAGE_SIZE);
+	kunmap_atomic(ptr, KM_USER1);
+
+	return 0;
+}
+
+/**
+ * read_pages_contents - read in data of pages in page-array chain
+ * @ctx - restart context
+ */
+static int read_pages_contents(struct ckpt_ctx *ctx)
+{
+	struct mm_struct *mm = current->mm;
+	struct ckpt_pgarr *pgarr;
+	unsigned long *vaddrs;
+	char *buf;
+	int i, ret = 0;
+
+	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	down_read(&mm->mmap_sem);
+	list_for_each_entry_reverse(pgarr, &ctx->pgarr_list, list) {
+		vaddrs = pgarr->vaddrs;
+		for (i = 0; i < pgarr->nr_used; i++) {
+			struct page *page;
+
+			_ckpt_debug(CKPT_DPAGE, "got page %#lx\n", vaddrs[i]);
+			ret = get_user_pages(current, mm, vaddrs[i],
+					     1, 1, 1, &page, NULL);
+			if (ret < 0)
+				goto out;
+
+			ret = restore_read_page(ctx, page, buf);
+			page_cache_release(page);
+
+			if (ret < 0)
+				goto out;
+		}
+	}
+
+ out:
+	up_read(&mm->mmap_sem);
+	kfree(buf);
+	return 0;
+}
+
+/**
+ * restore_private_contents - restore contents of a VMA with private memory
+ * @ctx - restart context
+ *
+ * Reads a header that specifies how many pages will follow, then reads
+ * a list of virtual addresses into ctx->pgarr_list page-array chain,
+ * followed by the actual contents of the corresponding pages. Iterates
+ * these steps until reaching a header specifying "0" pages, which marks
+ * the end of the contents.
+ */
+static int restore_private_contents(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_pgarr *h;
+	unsigned long nr_pages;
+	int ret = 0;
+
+	while (1) {
+		h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_PGARR);
+		if (IS_ERR(h))
+			break;
+
+		ckpt_debug("total pages %ld\n", (unsigned long) h->nr_pages);
+
+		nr_pages = h->nr_pages;
+		ckpt_hdr_put(ctx, h);
+
+		if (!nr_pages)
+			break;
+
+		ret = read_pages_vaddrs(ctx, nr_pages);
+		if (ret < 0)
+			break;
+		ret = read_pages_contents(ctx);
+		if (ret < 0)
+			break;
+		pgarr_reset_all(ctx);
+	}
+
+	return ret;
+}
+
+/**
+ * calc_map_prot_bits - convert vm_flags to mmap protection
+ * orig_vm_flags: source vm_flags
+ */
+static unsigned long calc_map_prot_bits(unsigned long orig_vm_flags)
+{
+	unsigned long vm_prot = 0;
+
+	if (orig_vm_flags & VM_READ)
+		vm_prot |= PROT_READ;
+	if (orig_vm_flags & VM_WRITE)
+		vm_prot |= PROT_WRITE;
+	if (orig_vm_flags & VM_EXEC)
+		vm_prot |= PROT_EXEC;
+	if (orig_vm_flags & PROT_SEM)   /* only (?) with IPC-SHM  */
+		vm_prot |= PROT_SEM;
+
+	return vm_prot;
+}
+
+/**
+ * calc_map_flags_bits - convert vm_flags to mmap flags
+ * orig_vm_flags: source vm_flags
+ */
+static unsigned long calc_map_flags_bits(unsigned long orig_vm_flags)
+{
+	unsigned long vm_flags = 0;
+
+	vm_flags = MAP_FIXED;
+	if (orig_vm_flags & VM_GROWSDOWN)
+		vm_flags |= MAP_GROWSDOWN;
+	if (orig_vm_flags & VM_DENYWRITE)
+		vm_flags |= MAP_DENYWRITE;
+	if (orig_vm_flags & VM_EXECUTABLE)
+		vm_flags |= MAP_EXECUTABLE;
+	if (orig_vm_flags & VM_MAYSHARE)
+		vm_flags |= MAP_SHARED;
+	else
+		vm_flags |= MAP_PRIVATE;
+
+	return vm_flags;
+}
+
+/**
+ * generic_vma_restore - restore a vma
+ * @mm - address space
+ * @file - file to map (NULL for anonymous)
+ * @h - vma header data
+ */
+static unsigned long generic_vma_restore(struct mm_struct *mm,
+					 struct file *file,
+					 struct ckpt_hdr_vma *h)
+{
+	unsigned long vm_size, vm_start, vm_flags, vm_prot, vm_pgoff;
+	unsigned long addr;
+
+	if (h->vm_end < h->vm_start)
+		return -EINVAL;
+	if (h->vm_flags & CKPT_VMA_NOT_SUPPORTED)
+		return -ENOSYS;
+
+	vm_start = h->vm_start;
+	vm_pgoff = h->vm_pgoff;
+	vm_size = h->vm_end - h->vm_start;
+	vm_prot = calc_map_prot_bits(h->vm_flags);
+	vm_flags = calc_map_flags_bits(h->vm_flags);
+
+	down_write(&mm->mmap_sem);
+	addr = do_mmap_pgoff(file, vm_start, vm_size,
+			     vm_prot, vm_flags, vm_pgoff);
+	up_write(&mm->mmap_sem);
+	ckpt_debug("size %#lx prot %#lx flag %#lx pgoff %#lx => %#lx\n",
+		 vm_size, vm_prot, vm_flags, vm_pgoff, addr);
+
+	return addr;
+}
+
+/**
+ * private_vma_restore - read vma data, recreate it and read contents
+ * @ctx: checkpoint context
+ * @mm: memory address space
+ * @file: file to use for mapping
+ * @h - vma header data
+ */
+int private_vma_restore(struct ckpt_ctx *ctx, struct mm_struct *mm,
+			struct file *file, struct ckpt_hdr_vma *h)
+{
+	unsigned long addr;
+
+	if (h->vm_flags & VM_SHARED)
+		return -EINVAL;
+
+	addr = generic_vma_restore(mm, file, h);
+	if (IS_ERR((void *) addr))
+		return PTR_ERR((void *) addr);
+
+	return restore_private_contents(ctx);
+}
+
+/**
+ * anon_private_restore - read vma data, recreate it and read contents
+ * @ctx: checkpoint context
+ * @mm: memory address space
+ * @h - vma header data
+ */
+static int anon_private_restore(struct ckpt_ctx *ctx,
+				     struct mm_struct *mm,
+				     struct ckpt_hdr_vma *h)
+{
+	/*
+	 * vm_pgoff for anonymous mapping is the "global" page
+	 * offset (namely from addr 0x0), so we force a zero
+	 */
+	h->vm_pgoff = 0;
+
+	return private_vma_restore(ctx, mm, NULL, h);
+}
+
+/* callbacks to restore vma per its type: */
+struct restore_vma_ops {
+	char *vma_name;
+	enum vma_type vma_type;
+	int (*restore) (struct ckpt_ctx *ctx,
+			struct mm_struct *mm,
+			struct ckpt_hdr_vma *ptr);
+};
+
+static struct restore_vma_ops restore_vma_ops[] = {
+	/* ignored vma */
+	{
+		.vma_name = "IGNORE",
+		.vma_type = CKPT_VMA_IGNORE,
+		.restore = NULL,
+	},
+	/* special mapping (vdso) */
+	{
+		.vma_name = "VDSO",
+		.vma_type = CKPT_VMA_VDSO,
+		.restore = special_mapping_restore,
+	},
+	/* anonymous private */
+	{
+		.vma_name = "ANON PRIVATE",
+		.vma_type = CKPT_VMA_ANON,
+		.restore = anon_private_restore,
+	},
+	/* file-mapped private */
+	{
+		.vma_name = "FILE PRIVATE",
+		.vma_type = CKPT_VMA_FILE,
+		.restore = filemap_restore,
+	},
+};
+
+/**
+ * restore_vma - read vma data, recreate it and read contents
+ * @ctx: checkpoint context
+ * @mm: memory address space
+ */
+static int restore_vma(struct ckpt_ctx *ctx, struct mm_struct *mm)
+{
+	struct ckpt_hdr_vma *h;
+	struct restore_vma_ops *ops;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_VMA);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ckpt_debug("vma %#lx-%#lx type %d\n", (unsigned long) h->vm_start,
+		 (unsigned long) h->vm_end, (int) h->vma_type);
+
+	ret = -EINVAL;
+	if (h->vm_end < h->vm_start)
+		goto out;
+	if (h->vma_type >= CKPT_VMA_MAX)
+		goto out;
+
+	ops = &restore_vma_ops[h->vma_type];
+
+	/* make sure we don't change this accidentally */
+	BUG_ON(ops->vma_type != h->vma_type);
+
+	if (ops->restore) {
+		ckpt_debug("vma type %s\n", ops->vma_name);
+		ret = ops->restore(ctx, mm, h);
+	} else {
+		ckpt_debug("vma ignored\n");
+		ret = 0;
+	}
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+static int destroy_mm(struct mm_struct *mm)
+{
+	struct vm_area_struct *vmnext = mm->mmap;
+	struct vm_area_struct *vma;
+	int ret;
+
+	while (vmnext) {
+		vma = vmnext;
+		vmnext = vmnext->vm_next;
+		ret = do_munmap(mm, vma->vm_start, vma->vm_end-vma->vm_start);
+		if (ret < 0) {
+			pr_warning("c/r: failed do_munmap (%d)\n", ret);
+			return ret;
+		}
+	}
+	return 0;
+}
+
+int restore_mm(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_mm *h;
+	struct mm_struct *mm;
+	unsigned int nr;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_MM);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ckpt_debug("map_count %d\n", h->map_count);
+
+	/* XXX need more sanity checks */
+
+	ret = -EINVAL;
+	if ((h->start_code > h->end_code) ||
+	    (h->start_data > h->end_data))
+		goto out;
+
+	mm = current->mm;
+
+	/* point of no return -- destruct current mm */
+	down_write(&mm->mmap_sem);
+	ret = destroy_mm(mm);
+	if (ret < 0) {
+		up_write(&mm->mmap_sem);
+		goto out;
+	}
+	mm->start_code = h->start_code;
+	mm->end_code = h->end_code;
+	mm->start_data = h->start_data;
+	mm->end_data = h->end_data;
+	mm->start_brk = h->start_brk;
+	mm->brk = h->brk;
+	mm->start_stack = h->start_stack;
+	mm->arg_start = h->arg_start;
+	mm->arg_end = h->arg_end;
+	mm->env_start = h->env_start;
+	mm->env_end = h->env_end;
+	up_write(&mm->mmap_sem);
+
+	/* FIX: need also mm->flags */
+
+	for (nr = h->map_count; nr; nr--) {
+		ret = restore_vma(ctx, mm);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = restore_mm_context(ctx, mm);
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
diff --git a/checkpoint/process.c b/checkpoint/process.c
index 64deb76..7adb842 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -108,6 +108,10 @@ int restore_task(struct ckpt_ctx *ctx)
 	ckpt_debug("ret %d\n", ret);
 	if (ret < 0)
 		goto out;
+	ret = restore_mm(ctx);
+	ckpt_debug("memory: ret %d\n", ret);
+	if (ret < 0)
+		goto out;
 	ret = restore_thread(ctx);
 	ckpt_debug("thread: ret %d\n", ret);
 	if (ret < 0)
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index 9adcc90..a1ab0a1 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -287,10 +287,19 @@ static int restore_read_tail(struct ckpt_ctx *ctx)
 	return ret;
 }
 
+/* setup restart-specific parts of ctx */
+static int ckpt_ctx_restart(struct ckpt_ctx *ctx)
+{
+	return 0;
+}
+
 int do_restart(struct ckpt_ctx *ctx, pid_t pid)
 {
 	int ret;
 
+	ret = ckpt_ctx_restart(ctx);
+	if (ret < 0)
+		return ret;
 	ret = restore_read_header(ctx);
 	if (ret < 0)
 		return ret;
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 108e6a1..73b34af 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -51,7 +51,11 @@ extern int private_vma_checkpoint(struct ckpt_ctx *ctx,
 				  struct vm_area_struct *vma,
 				  enum vma_type type);
 
+extern int private_vma_restore(struct ckpt_ctx *ctx, struct mm_struct *mm,
+			       struct file *file, struct ckpt_hdr_vma *h);
+
 extern int checkpoint_mm(struct ckpt_ctx *ctx, struct task_struct *t);
+extern int restore_mm(struct ckpt_ctx *ctx);
 
 #define CKPT_VMA_NOT_SUPPORTED					\
 	(VM_SHARED | VM_MAYSHARE | VM_IO | VM_HUGETLB |		\
@@ -61,6 +65,7 @@ extern int checkpoint_mm(struct ckpt_ctx *ctx, struct task_struct *t);
 
 /* files */
 extern int checkpoint_file(struct ckpt_ctx *ctx, struct file *file);
+extern struct file *restore_file(struct ckpt_ctx *ctx);
 
 
 /* debugging flags */
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index dab6b7f..5266e4b 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -114,11 +114,13 @@ struct ckpt_hdr_mm {
 	__u64 arg_start, arg_end, env_start, env_end;
 } __attribute__((aligned(8)));
 
-/* vma subtypes */
+/* vma subtypes - index into restore_vma_dispatch[] */
 enum vma_type {
-	CKPT_VMA_VDSO = 1,	/* special vdso vma */
+	CKPT_VMA_IGNORE = 0,
+	CKPT_VMA_VDSO,		/* special vdso vma */
 	CKPT_VMA_ANON,		/* private anonymous */
 	CKPT_VMA_FILE,		/* private mapped file */
+	CKPT_VMA_MAX,
 };
 
 /* vma decsriptor */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 05f0ed9..585d398 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1182,6 +1182,15 @@ extern int filemap_fault(struct vm_area_struct *, struct vm_fault *);
 int write_one_page(struct page *page, int wait);
 void task_dirty_inc(struct task_struct *tsk);
 
+
+/* checkpoint/restart */
+#ifdef CONFIG_CHECKPOINT
+extern int filemap_restore(struct ckpt_ctx *ctx, struct mm_struct *mm,
+			   struct ckpt_hdr_vma *hh);
+extern int special_mapping_restore(struct ckpt_ctx *ctx, struct mm_struct *mm,
+				   struct ckpt_hdr_vma *hh);
+#endif
+
 /* readahead.c */
 #define VM_MAX_READAHEAD	128	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
diff --git a/mm/filemap.c b/mm/filemap.c
index 2b58027..ef5680b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1650,6 +1650,24 @@ static int filemap_checkpoint(struct ckpt_ctx *ctx,
  out:
 	return ret;
 }
+
+int filemap_restore(struct ckpt_ctx *ctx,
+		    struct mm_struct *mm,
+		    struct ckpt_hdr_vma *h)
+{
+	struct file *file;
+	int ret;
+
+	/* for private mapping using 'read-only' is sufficient */
+	file = restore_file(ctx);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	ret = private_vma_restore(ctx, mm, file, h);
+
+	fput(file);
+	return ret;
+}
 #else
 #define filemap_checkpoint NULL
 #endif /* CONFIG_CHECKPOINT */
diff --git a/mm/mmap.c b/mm/mmap.c
index 6b75359..3b6356c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2114,7 +2114,7 @@ void exit_mmap(struct mm_struct *mm)
 	tlb = tlb_gather_mmu(mm, 1);
 	/* update_hiwater_rss(mm) here? but nobody should be looking */
 	/* Use -1 here to ensure all VMAs in the mm are unmapped */
-	end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
+	end = vma ? unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL) : 0;
 	vm_unacct_memory(nr_accounted);
 	free_pgtables(tlb, vma, FIRST_USER_ADDRESS, 0);
 	tlb_finish_mmu(tlb, 0, end);
@@ -2272,13 +2272,22 @@ static void special_mapping_close(struct vm_area_struct *vma)
 {
 }
 
-#if CONFIG_CHEKCPOINT
+#ifdef CONFIG_CHECKPOINT
+/*
+ * FIX:
+ *   - checkpoint vdso pages (once per distinct vdso is enough)
+ *   - check for compatilibility between saved and current vdso
+ *   - accommodate for dynamic kernel data in vdso page
+ *
+ * Current, we require COMPAT_VDSO which somewhat mitigates the issue
+ */
 static int special_mapping_checkpoint(struct ckpt_ctx *ctx,
 				      struct vm_area_struct *vma)
 {
-	char *name;
+	const char *name;
 
 	/*
+	 * FIX:
 	 * Currently, we only handle VDSO/vsyscall special handling.
 	 * Even that, is very basic - we just skip the contents and
 	 * hope for the best in terms of compatilibity upon restart.
@@ -2288,11 +2297,24 @@ static int special_mapping_checkpoint(struct ckpt_ctx *ctx,
 		return -ENOSYS;
 
 	name = arch_vma_name(vma);
-	if (!name || strcmp(vma_name, "[vdso]"))
+	if (!name || strcmp(name, "[vdso]"))
 		return -ENOSYS;
 
 	return generic_vma_checkpoint(ctx, vma, CKPT_VMA_VDSO);
 }
+
+int special_mapping_restore(struct ckpt_ctx *ctx,
+			    struct mm_struct *mm,
+			    struct ckpt_hdr_vma *h)
+{
+	/*
+	 * FIX:
+	 * Currently, we only handle VDSO/vsyscall special handling.
+	 * Even that, is very basic - call arch_setup_additional_pages
+	 * requiring the same mapping (start address) as before.
+	 */
+	return arch_setup_additional_pages(NULL, h->vm_start, 0);
+}
 #else
 #define special_mapping_checkpoint NULL
 #endif /* CONFIG_CHECKPOINT */
-- 
1.5.4.3