• Huang Ying's avatar
    kexec jump: save/restore device state · 89081d17
    Huang Ying authored
    This patch implements devices state save/restore before after kexec.
    
    This patch together with features in kexec_jump patch can be used for
    following:
    
    - A simple hibernation implementation without ACPI support.  You can kexec a
      hibernating kernel, save the memory image of original system and shutdown
      the system.  When resuming, you restore the memory image of original system
      via ordinary kexec load then jump back.
    
    - Kernel/system debug through making system snapshot.  You can make system
      snapshot, jump back, do some thing and make another system snapshot.
    
    - Cooperative multi-kernel/system.  With kexec jump, you can switch between
      several kernels/systems quickly without boot process except the first time.
      This appears like swap a whole kernel/system out/in.
    
    - A general method to call program in physical mode (paging turning
      off). This can be used to invoke BIOS code under Linux.
    
    The following user-space tools can be used with kexec jump:
    
    - kexec-tools needs to be patched to support kexec jump. The patches
      and the precompiled kexec can be download from the following URL:
           source: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec-tools-src_git_kh10.tar.bz2
           patches: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec-tools-patches_git_kh10.tar.bz2
           binary: http://khibernation.sourceforge.net/download/release_v10/kexec-tools/kexec_git_kh10
    
    - makedumpfile with patches are used as memory image saving tool, it
      can exclude free pages from original kernel memory image file. The
      patches and the precompiled makedumpfile can be download from the
      following URL:
           source: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile-src_cvs_kh10.tar.bz2
           patches: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile-patches_cvs_kh10.tar.bz2
           binary: http://khibernation.sourceforge.net/download/release_v10/makedumpfile/makedumpfile_cvs_kh10
    
    - An initramfs image can be used as the root file system of kexeced
      kernel. An initramfs image built with "BuildRoot" can be downloaded
      from the following URL:
           initramfs image: http://khibernation.sourceforge.net/download/release_v10/initramfs/rootfs_cvs_kh10.gz
      All user space tools above are included in the initramfs image.
    
    Usage example of simple hibernation:
    
    1. Compile and install patched kernel with following options selected:
    
    CONFIG_X86_32=y
    CONFIG_RELOCATABLE=y
    CONFIG_KEXEC=y
    CONFIG_CRASH_DUMP=y
    CONFIG_PM=y
    CONFIG_HIBERNATION=y
    CONFIG_KEXEC_JUMP=y
    
    2. Build an initramfs image contains kexec-tool and makedumpfile, or
       download the pre-built initramfs image, called rootfs.gz in
       following text.
    
    3. Prepare a partition to save memory image of original kernel, called
       hibernating partition in following text.
    
    4. Boot kernel compiled in step 1 (kernel A).
    
    5. In the kernel A, load kernel compiled in step 1 (kernel B) with
       /sbin/kexec. The shell command line can be as follow:
    
       /sbin/kexec --load-preserve-context /boot/bzImage --mem-min=0x100000
         --mem-max=0xffffff --initrd=rootfs.gz
    
    6. Boot the kernel B with following shell command line:
    
       /sbin/kexec -e
    
    7. The kernel B will boot as normal kexec. In kernel B the memory
       image of kernel A can be saved into hibernating partition as
       follow:
    
       jump_back_entry=`cat /proc/cmdline | tr ' ' '\n' | grep kexec_jump_back_entry | cut -d '='`
       echo $jump_back_entry > kexec_jump_back_entry
       cp /proc/vmcore dump.elf
    
       Then you can shutdown the machine as normal.
    
    8. Boot kernel compiled in step 1 (kernel C). Use the rootfs.gz as
       root file system.
    
    9. In kernel C, load the memory image of kernel A as follow:
    
       /sbin/kexec -l --args-none --entry=`cat kexec_jump_back_entry` dump.elf
    
    10. Jump back to the kernel A as follow:
    
       /sbin/kexec -e
    
       Then, kernel A is resumed.
    
    Implementation point:
    
    To support jumping between two kernels, before jumping to (executing)
    the new kernel and jumping back to the original kernel, the devices
    are put into quiescent state, and the state of devices and CPU is
    saved. After jumping back from kexeced kernel and jumping to the new
    kernel, the state of devices and CPU are restored accordingly. The
    devices/CPU state save/restore code of software suspend is called to
    implement corresponding function.
    
    Known issues:
    
    - Because the segment number supported by sys_kexec_load is limited,
      hibernation image with many segments may not be load. This is
      planned to be eliminated by adding a new flag to sys_kexec_load to
      make a image can be loaded with multiple sys_kexec_load invoking.
    
    Now, only the i386 architecture is supported.
    Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
    Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Pavel Machek <pavel@ucw.cz>
    Cc: Nigel Cunningham <nigel@nigel.suspend2.net>
    Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    89081d17
machine_kexec_32.c 5.02 KB