khibernation - kexec based hibernation
Kexec base hibernation has some potential advantages over u/swsusp and
TuxOnIce (suspend2). Some of them are as follow:
1. The hibernation image size can exceed half of memory size
easily. This is possible with TuxOnIce, but impossible with
u/swsusp.
2. It is possible to eliminate freezer from kexec based hibernation
implementation, after corresponding changes to device drivers are
done.
3. Based on kexec/kdump implementation, the kernel code needed is
less.
Now, only the i386 architecture is supported. The patchset is based on
Linux kernel 2.6.24-rc4-mm1, and has been tested on IBM T42 with ACPI
on and off.
The following user-space tools are needed to implement hibernation and
resume.
1. kexec-tools needs to be patched to support khibernation. The patches
and the precompiled kexec can be download from the following URL:
source: http://khibernation.sourceforge.net/download/release_v7/kexec-tools/kexec-tools-src_git_kh7.tar.bz2
patches: http://khibernation.sourceforge.net/download/release_v7/kexec-tools/kexec-tools-patches_git_kh7.tar.bz2
binary: http://khibernation.sourceforge.net/download/release_v7/kexec-tools/kexec_git_kh7
2. makedumpfile with patches are used as memory image saving tool, it
can exclude free pages from hibernation image file. The patches and
the precompiled makedumpfile can be download from the following
URL:
source: http://khibernation.sourceforge.net/download/release_v7/makedumpfile/makedumpfile-src_cvs_kh7.tar.bz2
patches: http://khibernation.sourceforge.net/download/release_v7/makedumpfile/makedumpfile-patches_cvs_kh7.tar.bz2
binary: http://khibernation.sourceforge.net/download/release_v7/makedumpfile/makedumpfile_cvs_kh7
3. A simplest memory image restoring tool named "krestore" is
implemented. It can be downloaded from the following URL:
source: http://khibernation.sourceforge.net/download/release_v7/krestore/krestore-src_cvs_kh7.tar.bz2
binary: http://khibernation.sourceforge.net/download/release_v7/krestore/krestore_cvs_kh7
4. A simplest jumping back image (hibernation image is a kind of
jumping back image) parameter dump tool name "kjump_back_param" is
implemented. It can be download from the following URL:
source: http://khibernation.sourceforge.net/download/release_v7/kjump_back_param/kjump_back_param-src_cvs_kh7.tar.bz2
binary: http://khibernation.sourceforge.net/download/release_v7/kjump_back_param/kjump_back_param_cvs_kh7
An initramfs image is used as the root file system of
hibernating/resuming kernel. So, all user space tools above are needed
in initramfs. An initramfs image built with "BuildRoot" can be
downloaded from the following URL:
initramfs image: http://khibernation.sourceforge.net/download/release_v7/initramfs/rootfs_cvs_kh7.gz
Usage:
1. Compile and install patched kernel with following options selected:
CONFIG_X86_32=y
CONFIG_RELOCATABLE=y # not needed strictly, but it is more convenient with it
CONFIG_KEXEC=y
CONFIG_CRASH_DUMP=y # only needed by kexeced kernel to save/restore memory image
CONFIG_PM=y
CONFIG_HIBERNATION=y
2. Build an initramfs image contains all needed user space tools. Or,
download the pre-built initramfs image.
3. Prepare a raw partition (without file system, called hibernating
partition in following text) used to store memory image of
hibernated kernel. Caution!!! The contents of the partition will be
overwritten during hibernating.
4. Build a memory image of hibernating kernel. This memory image need
only to be built once unless the hardware configuration is changed.
4.1. Boot kernel compiled for normal usage (kernel A).
4.2. Load kernel compiled for hibernating/resuming usage (kernel B)
with kexec, the same kernel as that of 4 can be used if
CONFIG_RELOCATABLE=y and CONFIG_CRASH_DUMP=y are selected.
The --elf64-core-headers should be specified in command line
of kexec, because only the 64bit ELF is supported by krestore
tool. The "go_to_hibernate" should be specified in kernel
command line to trigger the hibernating automatically. The
major and minor device number of hibernating partition should
be specified in kernel command line through "khdev=<ma>:<mi>".
For example, the shell command line can be as follow:
kexec --load-jump-back /boot/bzImage --mem-min=0x100000
--mem-max=0xffffff --elf64-core-headers --append="khdev=3:7 go_to_hibernate"
4.3. Jump to the hibernating kernel (kernel B) with following shell
command line:
kexec -e
4.4. After normal boot process, the hibernation kernel will jump
back to hibernated kernel automatically. Then, the memory
image of hibernating kernel can be built with following shell
command line.
cp /proc/kimgcore .
5. Boot kernel compiled for normal usage (kernel A).
6. Load the memory image of hibernating kernel with following shell
command line:
kexec -l --args-none --flags=0x3e kimgcore
7. Start the real hibernating process with following shell command line:
kexec -e -c 0x6b630001
The hibernating kernel will write the memory image of hibernated
kernel and go to ACPI S4 state automatically.
8. Boot kernel (kernel C) compiled for hibernating/resuming usage in
memory range of kernel B.
The "go_to_resume" should be specified in kernel command line to
trigger the resuming process automatically. For example, the
following kernel command line parameters can be used:
memmap=exactmap memmap=640K@0K memmap=15M@1M mem=16M go_to_resume khdev=3:7
The initramfs should be used too. In GRUB, this can be specified
with following grub command:
initrd /boot/rootfs.gz
The resuming kernel will restore the memory image of hibernated
kernel and jump back to hibernated kernel automatically.
Known issues:
- The suspend/resume callback of device drivers are used to put
devices into quiescent state. This will unnecessarily (possibly
harmfully) put devices into low power state. This is intended to be
solved by separating device quiesce/unquiesce callback from the
device suspend/resume callback.
- The memory image of hibernated kernel must be saved in a separate
partition not used by hibernated kernel. This is planned to be
solved through making hibernating/resuming kernel write the memory
image to a file in partition used by hibernated kernel through block
list instead.
- The hibernating/resuming code are duplicated with current u/swsusp
code. They will be merged when kexec based hibernation goes more
stable.
- The setup of hibernate/resume is fairly complex. I will continue
working on simplifying.
TODO:
- Write the memory image to a file through block list instead of
ordinary file system operating.
- Merge duplicated code between kexec based hibernation and u/swsusp.
- Simplify hibernate/resume setup.
- Resume from hibernation with bootloader.
ChangeLog:
v7:
- Add an interface to dump the loaded kexec_image, which may contains
the memory image of kexeced system. This is used to accelerate kexec
based hibernation.
- Refactor kexec jump to be a command driven programming model.
- Adjust ACPI support to mimic the ACPI support of u/swsusp.
- Use kexec_lock to do synchronization.
v6:
- Add ACPI support.
- Refactor kexec jump to be a general facility to call real mode code.
v5:
- A flag (KEXEC_JUMP_BACK) is added to indicate the loaded kernel
image is used for jumping back. The reboot command for jumping back
is removed. This interface is more stable (proposed by Eric
Biederman).
- NX bit handling support for kexec is added.
- Merge machine_kexec and machine_kexec_jump, remove NO_RET attribute
from machine_kexec.
- Passing jump back entry to kexeced kernel via kernel command line
(parsed by user space tool via /proc/cmdline instead of
kernel). Original corresponding boot parameter and sysfs code is
removed.
v4:
- Two reboot command are merged back to one because the underlying
implementation is same.
- Jumping without reserving memory is implemented. As a side effect,
two direction jumping is implemented.
- A jump back protocol is defined and documented. The original kernel
and kexeced kernel are more independent from each other.
- The CPU state save/restore code are merged into relocate_kernel.S.
v3:
- The reboot command LINUX_REBOOT_CMD_KJUMP is split into to two
reboot command to reflect the different function.
- Document is added for added kernel parameters.
- /sys/kernel/kexec_jump_buf_pfn is made writable, it is used for
memory image restoring.
- Console restoring after jumping back is implemented.
- Writing support is added for /dev/oldmem, to restore memory contents
of hibernated system.
v2:
- The kexec jump implementation is put into the kexec/kdump framework
instead of software suspend framework. The device and CPU state
save/restore code of software suspend is called when needed.
- The same code path is used for both kexec a new kernel and jump back
to original kernel.
Best Regards,
Huang Ying
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