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[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 <or...@cs.columbia.edu>
---
 arch/x86/include/asm/Kbuild           |    1 +
 arch/x86/include/asm/checkpoint_hdr.h |  121 ++++++++
 arch/x86/include/asm/ptrace.h         |    5 +
 arch/x86/kernel/ptrace.c              |    8 +-
 arch/x86/mm/Makefile                  |    2 +
 arch/x86/mm/checkpoint.c              |  531 +++++++++++++++++++++++++++++++++
 checkpoint/checkpoint.c               |    7 +-
 checkpoint/process.c                  |   19 ++-
 checkpoint/restart.c                  |    6 +
 include/linux/checkpoint.h            |    9 +
 include/linux/checkpoint_hdr.h        |   16 +-
 11 files changed, 718 insertions(+), 7 deletions(-)
 create mode 100644 arch/x86/include/asm/checkpoint_hdr.h
 create mode 100644 arch/x86/mm/checkpoint.c

diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index 4a8e80c..f76cb6e 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..f4d1e14
--- /dev/null
+++ b/arch/x86/include/asm/checkpoint_hdr.h
@@ -0,0 +1,121 @@
+#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>
+#else
+#include <sys/user.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,
+};
+
+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;
+
+       /* debug registers */
+       __u64 debugreg0;
+       __u64 debugreg1;
+       __u64 debugreg2;
+       __u64 debugreg3;
+       __u64 debugreg6;
+       __u64 debugreg7;
+
+       /* 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/ptrace.h b/arch/x86/include/asm/ptrace.h
index 0f0d908..66b507b 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -242,6 +242,11 @@ extern void ptrace_bts_untrace(struct task_struct *tsk);
 #define arch_ptrace_untrace(tsk)       ptrace_bts_untrace(tsk)
 #endif /* CONFIG_X86_PTRACE_BTS */
 
+extern int ptrace_check_debugreg(int _32bit,
+                                unsigned long dr0, unsigned long dr1,
+                                unsigned long dr2, unsigned long dr3,
+                                unsigned long dr6, unsigned long dr7);
+
 #endif /* __KERNEL__ */
 
 #endif /* !__ASSEMBLY__ */
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 9b4cacf..3b434bd 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -466,10 +466,10 @@ static unsigned long ptrace_get_debugreg(struct 
task_struct *child, int n)
        return 0;
 }
 
-static int ptrace_check_debugreg(int _32bit,
-                                unsigned long dr0, unsigned long dr1,
-                                unsigned long dr2, unsigned long dr3,
-                                unsigned long dr6, unsigned long dr7)
+int ptrace_check_debugreg(int _32bit,
+                         unsigned long dr0, unsigned long dr1,
+                         unsigned long dr2, unsigned long dr3,
+                         unsigned long dr6, unsigned long dr7)
 {
        /* Breakpoint type: 00: --x, 01: -w-, 10: undefined, 11: rw- */
        unsigned int rw[4];
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index eefdeee..ddd5abb 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -21,3 +21,5 @@ obj-$(CONFIG_K8_NUMA)         += k8topology_64.o
 obj-$(CONFIG_ACPI_NUMA)                += srat_$(BITS).o
 
 obj-$(CONFIG_MEMTEST)          += memtest.o
+
+obj-$(CONFIG_CHECKPOINT)       += checkpoint.o
diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
new file mode 100644
index 0000000..023039f
--- /dev/null
+++ b/arch/x86/mm/checkpoint.c
@@ -0,0 +1,531 @@
+/*
+ *  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>
+
+/*
+ * helpers to encode/decode/validate registers/segments/eflags
+ */
+
+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)
+
+       if ((eflags & ~X86_EFLAGS_CKPT_MASK) != (X86_EFLAGS_IF | 0x2))
+               return 0;
+       return 1;
+}
+
+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;
+}
+
+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();
+}
+
+#define CKPT_X86_TIF_UNSUPPORTED   (_TIF_SECCOMP | _TIF_IO_BITMAP)
+
+/**************************************************************************
+ * Checkpoint
+ */
+
+static int may_checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+       if (t->thread.vm86_info) {
+               ckpt_write_err(ctx, "TE", "task in VM86 mode", -EBUSY);
+               return -EBUSY;
+       }
+       if (task_thread_info(t)->flags & CKPT_X86_TIF_UNSUPPORTED) {
+               ckpt_write_err(ctx, "TE", "bad thread info flags %#lx", -EBUSY);
+               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;
+}
+
+#ifdef CONFIG_X86_32
+
+static 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;
+       }
+}
+
+static void save_cpu_debug(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+       struct thread_struct *thread = &t->thread;
+
+       /* debug regs */
+
+       /*
+        * for checkpoint in process context (from within a container),
+        * get the actual registers; otherwise get the saved values.
+        */
+
+       if (t == current) {
+               get_debugreg(h->debugreg0, 0);
+               get_debugreg(h->debugreg1, 1);
+               get_debugreg(h->debugreg2, 2);
+               get_debugreg(h->debugreg3, 3);
+               get_debugreg(h->debugreg6, 6);
+               get_debugreg(h->debugreg7, 7);
+       } else {
+               h->debugreg0 = thread->debugreg0;
+               h->debugreg1 = thread->debugreg1;
+               h->debugreg2 = thread->debugreg2;
+               h->debugreg3 = thread->debugreg3;
+               h->debugreg6 = thread->debugreg6;
+               h->debugreg7 = thread->debugreg7;
+       }
+}
+
+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;
+}
+
+#endif /* CONFIG_X86_32 */
+
+/* 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 debug %d\n", h->used_math, !!h->debugreg7);
+
+       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;
+}
+
+#ifdef CONFIG_X86_32
+
+static 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 (!check_eflags(h->flags))
+               return -EINVAL;
+       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->flags = h->flags;
+       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;
+}
+
+static int load_cpu_debug(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+       int ret;
+
+       ret = ptrace_check_debugreg(1, h->debugreg0, h->debugreg1, h->debugreg2,
+                                   h->debugreg3, h->debugreg6, h->debugreg7);
+       if (ret < 0)
+               return ret;
+
+       set_debugreg(h->debugreg0, 0);
+       set_debugreg(h->debugreg1, 1);
+       /* ignore 4, 5 */
+       set_debugreg(h->debugreg2, 2);
+       set_debugreg(h->debugreg3, 3);
+       set_debugreg(h->debugreg6, 6);
+       set_debugreg(h->debugreg7, 7);
+
+       if (h->debugreg7)
+               set_tsk_thread_flag(t, TIF_DEBUG);
+       else
+               clear_tsk_thread_flag(t, TIF_DEBUG);
+
+       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;
+}
+
+#endif /* CONFIG_X86_32 */
+
+/* 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 debug %d\n", h->used_math, !!h->debugreg7);
+
+       ret = load_cpu_regs(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_hdr_put(ctx, h);
+       return ret;
+}
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index 57eb7d8..e228151 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -300,6 +300,8 @@ 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;
@@ -327,7 +329,10 @@ 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 checkpoint trailer */
diff --git a/checkpoint/process.c b/checkpoint/process.c
index d221c2a..1d1170c 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -57,6 +57,15 @@ 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 +106,14 @@ 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 9f08f4d..afe51c2 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -354,6 +354,8 @@ 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)
+               goto out;
        if (h->magic != CHECKPOINT_MAGIC_HEAD ||
            h->rev != CHECKPOINT_VERSION ||
            h->major != ((LINUX_VERSION_CODE >> 16) & 0xff) ||
@@ -382,6 +384,10 @@ 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 be0ba4b..aa8ce11 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -61,6 +61,15 @@ 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 22dadbd..92d082e 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -40,19 +40,33 @@ struct ckpt_hdr {
        __u32 len;
 } __attribute__((aligned(8)));
 
+
+#include <asm/checkpoint_hdr.h>
+
+
 /* header types */
 enum {
        CKPT_HDR_HEADER = 1,
+       CKPT_HDR_HEADER_ARCH,
        CKPT_HDR_BUFFER,
        CKPT_HDR_STRING,
 
        CKPT_HDR_TASK = 101,
+       CKPT_HDR_THREAD,
+       CKPT_HDR_CPU,
+
+       /* 201-299: reserved for arch-dependent */
 
        CKPT_HDR_TAIL = 9001,
 
        CKPT_HDR_ERROR = 9999,
 };
 
+/* architecture */
+enum {
+       CKPT_ARCH_X86_32 = 1,
+};
+
 /* kernel constants */
 struct ckpt_const {
        /* task */
@@ -68,7 +82,7 @@ struct ckpt_hdr_header {
        struct ckpt_hdr h;
        __u64 magic;
 
-       __u16 _padding;
+       __u16 arch_id;
 
        __u16 major;
        __u16 minor;
-- 
1.6.0.4

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