Re: [PATCH -mm 2/2] kexec jump -v11: save/restore device state

On Wed, 2008-06-11 at 12:30 -0400, Vivek Goyal wrote:
[...]

quoted

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

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.

Now it is not needed to have two boot-loader entries, just one is
enough. Step 4 and step 8 can share the same boot-loader entries. The
rootfs.gz can be the normal initramfs or initrd when deployment. In
rootfs.gz, if there is a valid hibernation image, the hibernated system
will be restored, otherwise, normal boot process follows.

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.


[..]

quoted

--- 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.

OK. I will add it.

Best Regards,
Huang Ying

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