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SubjectRe: [PATCH -mm 2/2] kexec jump -v11: save/restore device state
On Tue, Jun 10, 2008 at 03:15:06PM +0800, Huang, Ying wrote:
> 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:
> patches:
> binary:
> - 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:
> patches:
> binary:
> - 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:
> 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
> 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.

One of the concerns raised by hibernation people in the past was to use
single boot loader entry to boot normally as well while resuming a kernel.

So in this case a user either needs to maintain two boot-loader entries
or modify it on the fly. I wished there was a better way to handle that.

I am more interested in ability to have multiple kernel loaded in RAM
and capability to switch between them. Allows me to take non-disruptive
core dumps and somebody wanted to snapshots the kernels. That should
still work.

> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -125,6 +125,12 @@ void machine_kexec(struct kimage *image)
> /* Interrupts aren't acceptable while we reboot */
> local_irq_disable();
> + if (image->preserve_context) {
> +#ifdef CONFIG_X86_IO_APIC
> + disable_IO_APIC();
> +#endif

I think it would be a good idea to put some kind of comment here. We
need to put APICs in legacy mode so that we can get timer interrupts
in second kernel. kexec/kdump paths already have calls to
disable_IO_APIC() in one form or other. kexec jump path also needs one.


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