Message-Id: <1268842164-5590-25-git-send-email-orenl@cs.columbia.edu>
Date:	Wed, 17 Mar 2010 12:08:12 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Serge Hallyn <serue@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	containers@...ts.linux-foundation.org,
	Oren Laadan <orenl@...columbia.edu>
Subject: [C/R v20][PATCH 24/96] c/r: x86_32 support for checkpoint/restart

Add logic to save and restore architecture specific state, including
thread-specific state, CPU registers and FPU state.

In addition, architecture capabilities are saved in an architecure
specific extension of the header (ckpt_hdr_head_arch); Currently this
includes only FPU capabilities.

Currently only x86-32 is supported.

Changelog[v19]:
  - [Serge Hallyn] Use ckpt_err() for arch incompatbilities
Changelog[v19-rc3]:
  - Rebase to kernel 2.6.33:
    * Use PTREGSCALL4 for sys_{checkpoint,restart}
    * Remove debug-reg support (need to redo with perf_events)
  - [Serge Hallyn] Support for ia32 (checkpoint, restart)
  - Split arch/x86/checkpoint.c to generic and 32bit specific parts
  - sys_{checkpoint,restore} to use ptregs
Changelog[v19-rc1]:
  - Fix up headers so we can munge them for use by userspace
  - [Matt Helsley] Add cpp definitions for enums
  - Allow X86_EFLAGS_RF on restart
Changelog[v17]:
  - Fix compilation for architectures that don't support checkpoint
  - Validate cpu registers and TLS descriptors on restart
  - Validate debug registers on restart
  - Export asm/checkpoint_hdr.h to userspace
Changelog[v16]:
  - All objects are preceded by ckpt_hdr (TLS and xstate_buf)
  - Add architecture identifier to main header
Changelog[v14]:
  - Use new interface ckpt_hdr_get/put()
  - Embed struct ckpt_hdr in struct ckpt_hdr...
  - Remove preempt_disable/enable() around init_fpu() and fix leak
  - Revert change to pr_debug(), back to ckpt_debug()
  - Move code related to task_struct to checkpoint/process.c
Changelog[v12]:
  - A couple of missed calls to ckpt_hbuf_put()
  - Replace obsolete ckpt_debug() with pr_debug()
Changelog[v9]:
  - Add arch-specific header that details architecture capabilities;
    split FPU restore to send capabilities only once.
  - Test for zero TLS entries in ckpt_write_thread()
  - Fix asm/checkpoint_hdr.h so it can be included from user-space
Changelog[v7]:
  - Fix save/restore state of FPU
Changelog[v5]:
  - Remove preempt_disable() when restoring debug registers
Changelog[v4]:
  - Fix header structure alignment
Changelog[v2]:
  - Pad header structures to 64 bits to ensure compatibility
  - Follow Dave Hansen's refactoring of the original post

Signed-off-by: Oren Laadan <orenl@...columbia.edu>
Acked-by: Serge E. Hallyn <serue@...ibm.com>
Tested-by: Serge E. Hallyn <serue@...ibm.com>
---
 arch/x86/ia32/ia32entry.S             |    9 +
 arch/x86/include/asm/Kbuild           |    1 +
 arch/x86/include/asm/checkpoint_hdr.h |  112 +++++++++
 arch/x86/include/asm/syscalls.h       |    6 +
 arch/x86/include/asm/unistd_32.h      |    2 +
 arch/x86/kernel/Makefile              |    8 +
 arch/x86/kernel/checkpoint.c          |  420 +++++++++++++++++++++++++++++++++
 arch/x86/kernel/checkpoint_32.c       |  173 ++++++++++++++
 arch/x86/kernel/entry_32.S            |    8 +
 arch/x86/kernel/syscall_table_32.S    |    2 +
 checkpoint/checkpoint.c               |    7 +-
 checkpoint/process.c                  |   20 ++-
 checkpoint/restart.c                  |    8 +
 include/linux/checkpoint.h            |    9 +
 include/linux/checkpoint_hdr.h        |   20 ++-
 15 files changed, 801 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/include/asm/checkpoint_hdr.h
 create mode 100644 arch/x86/kernel/checkpoint.c
 create mode 100644 arch/x86/kernel/checkpoint_32.c

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 5eec1d9..738a930 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -478,6 +478,13 @@ quiet_ni_syscall:
 	PTREGSCALL stub32_vfork, sys_vfork, %rdi
 	PTREGSCALL stub32_iopl, sys_iopl, %rsi
 	PTREGSCALL stub32_eclone, sys_eclone, %r8
+#ifdef CONFIG_CHECKPOINT
+	PTREGSCALL stub32_checkpoint, sys_checkpoint, %r8
+	PTREGSCALL stub32_restart, sys_restart, %r8
+#else
+	PTREGSCALL stub32_checkpoint, sys_ni_syscall, %r8
+	PTREGSCALL stub32_restart, sys_ni_syscall, %r8
+#endif
 
 ENTRY(ia32_ptregs_common)
 	popq %r11
@@ -844,4 +851,6 @@ ia32_sys_call_table:
 	.quad sys_perf_event_open
 	.quad compat_sys_recvmmsg
 	.quad stub32_eclone
+	.quad stub32_checkpoint
+	.quad stub32_restart			/* 340 */
 ia32_syscall_end:
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index 9f828f8..3b90273 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -2,6 +2,7 @@ include include/asm-generic/Kbuild.asm
 
 header-y += boot.h
 header-y += bootparam.h
+header-y += checkpoint_hdr.h
 header-y += debugreg.h
 header-y += ldt.h
 header-y += msr-index.h
diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h
new file mode 100644
index 0000000..e6cfc99
--- /dev/null
+++ b/arch/x86/include/asm/checkpoint_hdr.h
@@ -0,0 +1,112 @@
+#ifndef __ASM_X86_CKPT_HDR_H
+#define __ASM_X86_CKPT_HDR_H
+/*
+ *  Checkpoint/restart - architecture specific headers x86
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#ifndef _CHECKPOINT_CKPT_HDR_H_
+#error asm/checkpoint_hdr.h included directly
+#endif
+
+#include <linux/types.h>
+
+/*
+ * To maintain compatibility between 32-bit and 64-bit architecture flavors,
+ * keep data 64-bit aligned: use padding for structure members, and use
+ * __attribute__((aligned (8))) for the entire structure.
+ *
+ * Quoting Arnd Bergmann:
+ *   "This structure has an odd multiple of 32-bit members, which means
+ *   that if you put it into a larger structure that also contains 64-bit
+ *   members, the larger structure may get different alignment on x86-32
+ *   and x86-64, which you might want to avoid. I can't tell if this is
+ *   an actual problem here. ... In this case, I'm pretty sure that
+ *   sizeof(ckpt_hdr_task) on x86-32 is different from x86-64, since it
+ *   will be 32-bit aligned on x86-32."
+ */
+
+/* i387 structure seen from kernel/userspace */
+#ifdef __KERNEL__
+#include <asm/processor.h>
+#endif
+
+#ifdef CONFIG_X86_32
+#define CKPT_ARCH_ID	CKPT_ARCH_X86_32
+#endif
+
+/* arch dependent header types */
+enum {
+	CKPT_HDR_CPU_FPU = 201,
+#define CKPT_HDR_CPU_FPU CKPT_HDR_CPU_FPU
+};
+
+struct ckpt_hdr_header_arch {
+	struct ckpt_hdr h;
+	/* FIXME: add HAVE_HWFP */
+	__u16 has_fxsr;
+	__u16 has_xsave;
+	__u16 xstate_size;
+	__u16 _pading;
+} __attribute__((aligned(8)));
+
+struct ckpt_hdr_thread {
+	struct ckpt_hdr h;
+	__u32 thread_info_flags;
+	__u16 gdt_entry_tls_entries;
+	__u16 sizeof_tls_array;
+} __attribute__((aligned(8)));
+
+/* designed to work for both x86_32 and x86_64 */
+struct ckpt_hdr_cpu {
+	struct ckpt_hdr h;
+	/* see struct pt_regs (x86_64) */
+	__u64 r15;
+	__u64 r14;
+	__u64 r13;
+	__u64 r12;
+	__u64 bp;
+	__u64 bx;
+	__u64 r11;
+	__u64 r10;
+	__u64 r9;
+	__u64 r8;
+	__u64 ax;
+	__u64 cx;
+	__u64 dx;
+	__u64 si;
+	__u64 di;
+	__u64 orig_ax;
+	__u64 ip;
+	__u64 sp;
+
+	__u64 flags;
+
+	/* segment registers */
+	__u64 fs;
+	__u64 gs;
+
+	__u16 fsindex;
+	__u16 gsindex;
+	__u16 cs;
+	__u16 ss;
+	__u16 ds;
+	__u16 es;
+
+	__u32 used_math;
+
+	/* thread_xstate contents follow (if used_math) */
+} __attribute__((aligned(8)));
+
+#define CKPT_X86_SEG_NULL	0
+#define CKPT_X86_SEG_USER32_CS	1
+#define CKPT_X86_SEG_USER32_DS	2
+#define CKPT_X86_SEG_TLS	0x4000	/* 0100 0000 0000 00xx */
+#define CKPT_X86_SEG_LDT	0x8000	/* 100x xxxx xxxx xxxx */
+
+#endif /* __ASM_X86_CKPT_HDR__H */
diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
index 972ab0e..c71262e 100644
--- a/arch/x86/include/asm/syscalls.h
+++ b/arch/x86/include/asm/syscalls.h
@@ -29,6 +29,12 @@ long sys_clone(unsigned long, unsigned long, void __user *,
 	       void __user *, struct pt_regs *);
 long sys_eclone(unsigned flags_low, struct clone_args __user *uca,
 		int args_size, pid_t __user *pids, struct pt_regs *regs);
+#ifdef CONFIG_CHECKPOINT
+long sys_checkpoint(pid_t pid, int fd, unsigned long flags,
+		    int logfd, struct pt_regs *regs);
+long sys_restart(pid_t pid, int fd, unsigned long flags,
+		 int logfd, struct pt_regs *regs);
+#endif
 
 /* kernel/ldt.c */
 asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h
index a66ed15..55b7cae 100644
--- a/arch/x86/include/asm/unistd_32.h
+++ b/arch/x86/include/asm/unistd_32.h
@@ -344,6 +344,8 @@
 #define __NR_perf_event_open	336
 #define __NR_recvmmsg		337
 #define __NR_eclone		338
+#define __NR_checkpoint		339
+#define __NR_restart		340
 
 #ifdef __KERNEL__
 
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index d87f09b..2f45350 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -116,6 +116,14 @@ obj-$(CONFIG_X86_CHECK_BIOS_CORRUPTION) += check.o
 
 obj-$(CONFIG_SWIOTLB)			+= pci-swiotlb.o
 
+obj-$(CONFIG_CHECKPOINT)	+= checkpoint.o
+
+###
+# 32 bit specific files
+ifeq ($(CONFIG_X86_32),y)
+	obj-$(CONFIG_CHECKPOINT)	+= checkpoint_32.o
+endif
+
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/checkpoint.c b/arch/x86/kernel/checkpoint.c
new file mode 100644
index 0000000..06fe740
--- /dev/null
+++ b/arch/x86/kernel/checkpoint.c
@@ -0,0 +1,420 @@
+/*
+ *  Checkpoint/restart - architecture specific support for x86
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
+#include <asm/desc.h>
+#include <asm/i387.h>
+
+#include <linux/checkpoint.h>
+#include <linux/checkpoint_hdr.h>
+
+
+/*
+ * sys_checkpoint needs to be a ptregscall to match sys_restart
+ * so self-checkpoint images can be restarted.
+ */
+long sys_checkpoint(pid_t pid, int fd, unsigned long flags, int logfd,
+		    struct pt_regs *regs)
+{
+	return do_sys_checkpoint(pid, fd, flags, logfd);
+}
+
+/*
+ * sys_restart needs to access and modify the pt_regs structure to
+ * restore the original state from the time of the checkpoint.
+ */
+long sys_restart(pid_t pid, int fd, unsigned long flags, int logfd,
+		 struct pt_regs *regs)
+{
+	return do_sys_restart(pid, fd, flags, logfd);
+}
+
+
+extern int check_segment(__u16 seg);
+extern __u16 encode_segment(unsigned short seg);
+extern unsigned short decode_segment(__u16 seg);
+extern void save_cpu_regs(struct ckpt_hdr_cpu *h, struct task_struct *t);
+extern int load_cpu_regs(struct ckpt_hdr_cpu *h, struct task_struct *t);
+
+static int check_tls(struct desc_struct *desc)
+{
+	if (!desc->a && !desc->b)
+		return 1;
+	if (desc->l != 0 || desc->s != 1 || desc->dpl != 3)
+		return 0;
+	return 1;
+}
+
+#define CKPT_X86_TIF_UNSUPPORTED   (_TIF_SECCOMP | _TIF_IO_BITMAP)
+
+/**************************************************************************
+ * Checkpoint
+ */
+
+static int may_checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+#ifdef CONFIG_X86_32
+	if (t->thread.vm86_info) {
+		ckpt_err(ctx, -EBUSY, "%(T)Task in VM86 mode\n");
+		return -EBUSY;
+	}
+#endif
+
+	/* debugregs not (yet) supported */
+	if (test_tsk_thread_flag(t, TIF_DEBUG)) {
+		ckpt_err(ctx, -EBUSY, "%(T)Task with debugreg set\n");
+		return -EBUSY;
+	}
+
+	if (task_thread_info(t)->flags & CKPT_X86_TIF_UNSUPPORTED) {
+		ckpt_err(ctx, -EBUSY, "%(T)Bad thread info flags %#lx\n",
+			 task_thread_info(t)->flags);
+		return -EBUSY;
+	}
+	return 0;
+}
+
+/* dump the thread_struct of a given task */
+int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr_thread *h;
+	int tls_size;
+	int ret;
+
+	ret = may_checkpoint_thread(ctx, t);
+	if (ret < 0)
+		return ret;
+
+	tls_size = sizeof(t->thread.tls_array);
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h) + tls_size, CKPT_HDR_THREAD);
+	if (!h)
+		return -ENOMEM;
+
+	h->thread_info_flags =
+		task_thread_info(t)->flags & ~CKPT_X86_TIF_UNSUPPORTED;
+	h->gdt_entry_tls_entries = GDT_ENTRY_TLS_ENTRIES;
+	h->sizeof_tls_array = tls_size;
+
+	/* For simplicity dump the entire array */
+	memcpy(h + 1, t->thread.tls_array, tls_size);
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+static void save_cpu_debug(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	/*
+	 * FIXME: as of kernel 2.6.33 debug registers are handled via
+	 * perf_event interface. For neither, neither is supported.
+	 */
+}
+
+static void save_cpu_fpu(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	h->used_math = tsk_used_math(t) ? 1 : 0;
+}
+
+static int checkpoint_cpu_fpu(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, xstate_size + sizeof(*h),
+			      CKPT_HDR_CPU_FPU);
+	if (!h)
+		return -ENOMEM;
+
+	/* i387 + MMU + SSE logic */
+	preempt_disable();	/* needed it (t == current) */
+
+	/*
+	 * normally, no need to unlazy_fpu(), since TS_USEDFPU flag
+	 * was cleared when task was context-switched out...
+	 * except if we are in process context, in which case we do
+	 */
+	if (t == current && (task_thread_info(t)->status & TS_USEDFPU))
+		unlazy_fpu(current);
+
+	/*
+	 * For simplicity dump the entire structure.
+	 * FIX: need to be deliberate about what registers we are
+	 * dumping for traceability and compatibility.
+	 */
+	memcpy(h + 1, t->thread.xstate, xstate_size);
+	preempt_enable();	/* needed if (t == current) */
+
+	ret = ckpt_write_obj(ctx, h);
+	ckpt_hdr_put(ctx, h);
+
+	return ret;
+}
+
+/* dump the cpu state and registers of a given task */
+int checkpoint_cpu(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr_cpu *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_CPU);
+	if (!h)
+		return -ENOMEM;
+
+	save_cpu_regs(h, t);
+	save_cpu_debug(h, t);
+	save_cpu_fpu(h, t);
+
+	ckpt_debug("math %d\n", h->used_math);
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	if (ret < 0)
+		goto out;
+
+	if (h->used_math)
+		ret = checkpoint_cpu_fpu(ctx, t);
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+int checkpoint_write_header_arch(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_header_arch *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_HEADER_ARCH);
+	if (!h)
+		return -ENOMEM;
+
+	/* FPU capabilities */
+	h->has_fxsr = cpu_has_fxsr;
+	h->has_xsave = cpu_has_xsave;
+	h->xstate_size = xstate_size;
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+
+	return ret;
+}
+
+/**************************************************************************
+ * Restart
+ */
+
+/* read the thread_struct into the current task */
+int restore_thread(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_thread *h;
+	struct thread_struct *thread = &current->thread;
+	struct desc_struct *desc;
+	int tls_size;
+	int i, cpu, ret;
+
+	tls_size = sizeof(thread->tls_array);
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h) + tls_size, CKPT_HDR_THREAD);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ret = -EINVAL;
+	if (h->thread_info_flags & CKPT_X86_TIF_UNSUPPORTED)
+		goto out;
+	if (h->gdt_entry_tls_entries != GDT_ENTRY_TLS_ENTRIES)
+		goto out;
+	if (h->sizeof_tls_array != tls_size)
+		goto out;
+
+	/*
+	 * restore TLS by hand: why convert to struct user_desc if
+	 * sys_set_thread_entry() will convert it back ?
+	 */
+	desc = (struct desc_struct *) (h + 1);
+
+	for (i = 0; i < GDT_ENTRY_TLS_ENTRIES; i++) {
+		if (!check_tls(&desc[i]))
+			goto out;
+	}
+
+	cpu = get_cpu();
+	memcpy(thread->tls_array, desc, tls_size);
+	load_TLS(thread, cpu);
+	put_cpu();
+
+	/* TODO: restore TIF flags as necessary (e.g. TIF_NOTSC) */
+
+	ret = 0;
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+static int load_cpu_debug(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	/*
+	 * FIXME: as of kernel 2.6.33 debug registers are handled via
+	 * perf_event interface. For neither, neither is supported.
+	 */
+
+	return 0;
+}
+
+static int load_cpu_fpu(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	preempt_disable();
+
+	__clear_fpu(t);		/* in case we used FPU in user mode */
+
+	if (!h->used_math)
+		clear_used_math();
+
+	preempt_enable();
+	return 0;
+}
+
+static int restore_cpu_fpu(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr *h;
+	int ret;
+
+	/* init_fpu() eventually also calls set_used_math() */
+	ret = init_fpu(current);
+	if (ret < 0)
+		return ret;
+
+	h = ckpt_read_obj_type(ctx, xstate_size + sizeof(*h),
+			       CKPT_HDR_CPU_FPU);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	memcpy(t->thread.xstate, h + 1, xstate_size);
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+static int check_eflags(__u32 eflags)
+{
+#define X86_EFLAGS_CKPT_MASK  \
+	(X86_EFLAGS_CF | X86_EFLAGS_PF | X86_EFLAGS_AF | X86_EFLAGS_ZF | \
+	 X86_EFLAGS_SF | X86_EFLAGS_TF | X86_EFLAGS_DF | X86_EFLAGS_OF | \
+	 X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_ID | X86_EFLAGS_RF)
+
+	if ((eflags & ~X86_EFLAGS_CKPT_MASK) != (X86_EFLAGS_IF | 0x2))
+		return 0;
+	return 1;
+}
+
+static void restore_eflags(struct pt_regs *regs, __u32 eflags)
+{
+	/*
+	 * A task may have had X86_EFLAGS_RF set at checkpoint, .e.g:
+	 * 1) It ran in a KVM guest, and the guest was being debugged,
+	 * 2) The kernel was debugged using kgbd,
+	 * 3) From Intel's manual: "When calling an event handler,
+	 *    Intel 64 and IA-32 processors establish the value of the
+	 *    RF flag in the EFLAGS image pushed on the stack:
+	 *  - For any fault-class exception except a debug exception
+	 *    generated in response to an instruction breakpoint, the
+	 *    value pushed for RF is 1.
+	 *  - For any interrupt arriving after any iteration of a
+	 *    repeated string instruction but the last iteration, the
+	 *    value pushed for RF is 1.
+	 *  - For any trap-class exception generated by any iteration
+	 *    of a repeated string instruction but the last iteration,
+	 *    the value pushed for RF is 1.
+	 *  - For other cases, the value pushed for RF is the value
+	 *    that was in EFLAG.RF at the time the event handler was
+	 *    called.
+	 *  [from: http://www.intel.com/Assets/PDF/manual/253668.pdf]
+	 *
+	 * The RF flag may be set in EFLAGS by the hardware, or by
+	 * kvm/kgdb, or even by the user with ptrace or by setting a
+	 * suitable context when returning from a signal handler.
+	 *
+	 * Therefore, on restart we (1) prserve X86_EFLAGS_RF from
+	 * checkpoint time, and (2) preserve a X86_EFLAGS_RF of the
+	 * restarting process if it already exists on saved EFLAGS.
+	 * Disable preemption to protect EFLAG test-and-change.
+	 */
+	preempt_disable();
+	eflags |= (regs->flags & X86_EFLAGS_RF);
+	regs->flags = eflags;
+	preempt_enable();
+}
+
+static int load_cpu_eflags(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	struct pt_regs *regs = task_pt_regs(t);
+
+	if (!check_eflags(h->flags))
+		return -EINVAL;
+	restore_eflags(regs, h->flags);
+	return 0;
+}
+
+/* read the cpu state and registers for the current task */
+int restore_cpu(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_cpu *h;
+	struct task_struct *t = current;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_CPU);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ckpt_debug("math %d\n", h->used_math);
+
+	ret = load_cpu_regs(h, t);
+	if (ret < 0)
+		goto out;
+	ret = load_cpu_eflags(h, t);
+	if (ret < 0)
+		goto out;
+	ret = load_cpu_debug(h, t);
+	if (ret < 0)
+		goto out;
+	ret = load_cpu_fpu(h, t);
+	if (ret < 0)
+		goto out;
+
+	if (h->used_math)
+		ret = restore_cpu_fpu(ctx, t);
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+int restore_read_header_arch(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_header_arch *h;
+	int ret = 0;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_HEADER_ARCH);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	/* FIX: verify compatibility of architecture features */
+
+	/* verify FPU capabilities */
+	if (h->has_fxsr != cpu_has_fxsr ||
+	    h->has_xsave != cpu_has_xsave ||
+	    h->xstate_size != xstate_size) {
+		ret = -EINVAL;
+		ckpt_err(ctx, ret, "incompatible FPU capabilities");
+	}
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
diff --git a/arch/x86/kernel/checkpoint_32.c b/arch/x86/kernel/checkpoint_32.c
new file mode 100644
index 0000000..32cde34
--- /dev/null
+++ b/arch/x86/kernel/checkpoint_32.c
@@ -0,0 +1,173 @@
+/*
+ *  Checkpoint/restart - architecture specific support for x86_32
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
+#include <asm/desc.h>
+#include <asm/i387.h>
+#include <asm/elf.h>
+
+#include <linux/checkpoint.h>
+#include <linux/checkpoint_hdr.h>
+
+/* helpers to encode/decode/validate segments */
+
+static int check_segment(__u16 seg)
+{
+	int ret = 0;
+
+	switch (seg) {
+	case CKPT_X86_SEG_NULL:
+	case CKPT_X86_SEG_USER32_CS:
+	case CKPT_X86_SEG_USER32_DS:
+		return 1;
+	}
+	if (seg & CKPT_X86_SEG_TLS) {
+		seg &= ~CKPT_X86_SEG_TLS;
+		if (seg <= GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN)
+			ret = 1;
+	} else if (seg & CKPT_X86_SEG_LDT) {
+		seg &= ~CKPT_X86_SEG_LDT;
+		if (seg <= 0x1fff)
+			ret = 1;
+	}
+	return ret;
+}
+
+static __u16 encode_segment(unsigned short seg)
+{
+	if (seg == 0)
+		return CKPT_X86_SEG_NULL;
+	BUG_ON((seg & 3) != 3);
+
+	if (seg == __USER_CS)
+		return CKPT_X86_SEG_USER32_CS;
+	if (seg == __USER_DS)
+		return CKPT_X86_SEG_USER32_DS;
+
+	if (seg & 4)
+		return CKPT_X86_SEG_LDT | (seg >> 3);
+
+	seg >>= 3;
+	if (GDT_ENTRY_TLS_MIN <= seg && seg <= GDT_ENTRY_TLS_MAX)
+		return CKPT_X86_SEG_TLS | (seg - GDT_ENTRY_TLS_MIN);
+
+	printk(KERN_ERR "c/r: (decode) bad segment %#hx\n", seg);
+	BUG();
+}
+
+static unsigned short decode_segment(__u16 seg)
+{
+	if (seg == CKPT_X86_SEG_NULL)
+		return 0;
+	if (seg == CKPT_X86_SEG_USER32_CS)
+		return __USER_CS;
+	if (seg == CKPT_X86_SEG_USER32_DS)
+		return __USER_DS;
+
+	if (seg & CKPT_X86_SEG_TLS) {
+		seg &= ~CKPT_X86_SEG_TLS;
+		return ((GDT_ENTRY_TLS_MIN + seg) << 3) | 3;
+	}
+	if (seg & CKPT_X86_SEG_LDT) {
+		seg &= ~CKPT_X86_SEG_LDT;
+		return (seg << 3) | 7;
+	}
+	BUG();
+}
+
+void save_cpu_regs(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	struct thread_struct *thread = &t->thread;
+	struct pt_regs *regs = task_pt_regs(t);
+	unsigned long _gs;
+
+	h->bp = regs->bp;
+	h->bx = regs->bx;
+	h->ax = regs->ax;
+	h->cx = regs->cx;
+	h->dx = regs->dx;
+	h->si = regs->si;
+	h->di = regs->di;
+	h->orig_ax = regs->orig_ax;
+	h->ip = regs->ip;
+
+	h->flags = regs->flags;
+	h->sp = regs->sp;
+
+	h->cs = encode_segment(regs->cs);
+	h->ss = encode_segment(regs->ss);
+	h->ds = encode_segment(regs->ds);
+	h->es = encode_segment(regs->es);
+
+	/*
+	 * for checkpoint in process context (from within a container)
+	 * the GS segment register should be saved from the hardware;
+	 * otherwise it is already saved on the thread structure
+	 */
+	if (t == current)
+		_gs = get_user_gs(regs);
+	else
+		_gs = thread->gs;
+
+	h->fsindex = encode_segment(regs->fs);
+	h->gsindex = encode_segment(_gs);
+
+	/*
+	 * for checkpoint in process context (from within a container),
+	 * the actual syscall is taking place at this very moment; so
+	 * we (optimistically) subtitute the future return value (0) of
+	 * this syscall into the orig_eax, so that upon restart it will
+	 * succeed (or it will endlessly retry checkpoint...)
+	 */
+	if (t == current) {
+		BUG_ON(h->orig_ax < 0);
+		h->ax = 0;
+	}
+}
+
+int load_cpu_regs(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+	struct thread_struct *thread = &t->thread;
+	struct pt_regs *regs = task_pt_regs(t);
+
+	if (h->cs == CKPT_X86_SEG_NULL)
+		return -EINVAL;
+	if (!check_segment(h->cs) || !check_segment(h->ds) ||
+	    !check_segment(h->es) || !check_segment(h->ss) ||
+	    !check_segment(h->fsindex) || !check_segment(h->gsindex))
+		return -EINVAL;
+
+	regs->bp = h->bp;
+	regs->bx = h->bx;
+	regs->ax = h->ax;
+	regs->cx = h->cx;
+	regs->dx = h->dx;
+	regs->si = h->si;
+	regs->di = h->di;
+	regs->orig_ax = h->orig_ax;
+	regs->ip = h->ip;
+
+	regs->sp = h->sp;
+
+	regs->ds = decode_segment(h->ds);
+	regs->es = decode_segment(h->es);
+	regs->cs = decode_segment(h->cs);
+	regs->ss = decode_segment(h->ss);
+
+	regs->fs = decode_segment(h->fsindex);
+	regs->gs = decode_segment(h->gsindex);
+
+	thread->gs = regs->gs;
+	lazy_load_gs(regs->gs);
+
+	return 0;
+}
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 65e1735..49d6628 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -781,6 +781,14 @@ PTREGSCALL0(rt_sigreturn)
 PTREGSCALL2(vm86)
 PTREGSCALL1(vm86old)
 PTREGSCALL4(eclone)
+#ifdef CONFIG_CHECKPOINT
+PTREGSCALL4(checkpoint)
+PTREGSCALL4(restart)
+#else
+/* Use the weak defs in kernel/sys_ni.c */
+#define ptregs_checkpoint  sys_checkpoint
+#define ptregs_restart  sys_restart
+#endif
 
 /* Clone is an oddball.  The 4th arg is in %edi */
 	ALIGN;
diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S
index 22ae7ef..dc81ec9 100644
--- a/arch/x86/kernel/syscall_table_32.S
+++ b/arch/x86/kernel/syscall_table_32.S
@@ -338,3 +338,5 @@ ENTRY(sys_call_table)
 	.long sys_perf_event_open
 	.long sys_recvmmsg
 	.long ptregs_eclone
+	.long ptregs_checkpoint
+	.long ptregs_restart		/* 340 */
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index 2f8b038..c74b21e 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -126,6 +126,8 @@ static int checkpoint_write_header(struct ckpt_ctx *ctx)
 	do_gettimeofday(&ktv);
 	uts = utsname();
 
+	h->arch_id = cpu_to_le16(CKPT_ARCH_ID);  /* see asm/checkpoitn.h */
+
 	h->magic = CHECKPOINT_MAGIC_HEAD;
 	h->major = (LINUX_VERSION_CODE >> 16) & 0xff;
 	h->minor = (LINUX_VERSION_CODE >> 8) & 0xff;
@@ -153,7 +155,10 @@ static int checkpoint_write_header(struct ckpt_ctx *ctx)
 	ret = ckpt_write_buffer(ctx, uts->machine, sizeof(uts->machine));
  up:
 	up_read(&uts_sem);
-	return ret;
+	if (ret < 0)
+		return ret;
+
+	return checkpoint_write_header_arch(ctx);
 }
 
 /* write the container configuration section */
diff --git a/checkpoint/process.c b/checkpoint/process.c
index d221c2a..f6fb9d1 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -56,7 +56,15 @@ int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
 
 	ret = checkpoint_task_struct(ctx, t);
 	ckpt_debug("task %d\n", ret);
-
+	if (ret < 0)
+		goto out;
+	ret = checkpoint_thread(ctx, t);
+	ckpt_debug("thread %d\n", ret);
+	if (ret < 0)
+		goto out;
+	ret = checkpoint_cpu(ctx, t);
+	ckpt_debug("cpu %d\n", ret);
+ out:
 	ctx->tsk = NULL;
 	return ret;
 }
@@ -97,6 +105,14 @@ int restore_task(struct ckpt_ctx *ctx)
 
 	ret = restore_task_struct(ctx);
 	ckpt_debug("task %d\n", ret);
-
+	if (ret < 0)
+		goto out;
+	ret = restore_thread(ctx);
+	ckpt_debug("thread %d\n", ret);
+	if (ret < 0)
+		goto out;
+	ret = restore_cpu(ctx);
+	ckpt_debug("cpu %d\n", ret);
+ out:
 	return ret;
 }
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index 29e051c..38a9b04 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -368,6 +368,10 @@ static int restore_read_header(struct ckpt_ctx *ctx)
 		return PTR_ERR(h);
 
 	ret = -EINVAL;
+	if (le16_to_cpu(h->arch_id) != CKPT_ARCH_ID) {
+		ckpt_err(ctx, ret, "incompatible architecture id");
+		goto out;
+	}
 	if (h->magic != CHECKPOINT_MAGIC_HEAD ||
 	    h->rev != CHECKPOINT_VERSION ||
 	    h->major != ((LINUX_VERSION_CODE >> 16) & 0xff) ||
@@ -402,6 +406,10 @@ static int restore_read_header(struct ckpt_ctx *ctx)
 	if (ret < 0)
 		goto out;
 	ret = _ckpt_read_buffer(ctx, uts->machine, sizeof(uts->machine));
+	if (ret < 0)
+		goto out;
+
+	ret = restore_read_header_arch(ctx);
  out:
 	kfree(uts);
 	ckpt_hdr_put(ctx, h);
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 8591f79..3095431 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -68,6 +68,15 @@ extern long do_restart(struct ckpt_ctx *ctx, pid_t pid);
 extern int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t);
 extern int restore_task(struct ckpt_ctx *ctx);
 
+/* arch hooks */
+extern int checkpoint_write_header_arch(struct ckpt_ctx *ctx);
+extern int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t);
+extern int checkpoint_cpu(struct ckpt_ctx *ctx, struct task_struct *t);
+
+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);
+
 static inline int ckpt_validate_errno(int errno)
 {
 	return (errno >= 0) && (errno < MAX_ERRNO);
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 97330ec..2ab878a 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -48,10 +48,16 @@ struct ckpt_hdr {
 	__u32 len;
 } __attribute__((aligned(8)));
 
+
+#include <asm/checkpoint_hdr.h>
+
+
 /* header types */
 enum {
 	CKPT_HDR_HEADER = 1,
 #define CKPT_HDR_HEADER CKPT_HDR_HEADER
+	CKPT_HDR_HEADER_ARCH,
+#define CKPT_HDR_HEADER_ARCH CKPT_HDR_HEADER_ARCH
 	CKPT_HDR_CONTAINER,
 #define CKPT_HDR_CONTAINER CKPT_HDR_CONTAINER
 	CKPT_HDR_BUFFER,
@@ -61,6 +67,12 @@ enum {
 
 	CKPT_HDR_TASK = 101,
 #define CKPT_HDR_TASK CKPT_HDR_TASK
+	CKPT_HDR_THREAD,
+#define CKPT_HDR_THREAD CKPT_HDR_THREAD
+	CKPT_HDR_CPU,
+#define CKPT_HDR_CPU CKPT_HDR_CPU
+
+	/* 201-299: reserved for arch-dependent */
 
 	CKPT_HDR_TAIL = 9001,
 #define CKPT_HDR_TAIL CKPT_HDR_TAIL
@@ -69,6 +81,12 @@ enum {
 #define CKPT_HDR_ERROR CKPT_HDR_ERROR
 };
 
+/* architecture */
+enum {
+	CKPT_ARCH_X86_32 = 1,
+#define CKPT_ARCH_X86_32 CKPT_ARCH_X86_32
+};
+
 /* kernel constants */
 struct ckpt_const {
 	/* task */
@@ -84,7 +102,7 @@ struct ckpt_hdr_header {
 	struct ckpt_hdr h;
 	__u64 magic;
 
-	__u16 _padding;
+	__u16 arch_id;
 
 	__u16 major;
 	__u16 minor;
-- 
1.6.3.3

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