Re: [PATCH 1/4 -mm] kexec based hibernation -v7 : kexec jump

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Dec 07, 2007 at 03:53:30PM +0000, Huang, Ying wrote:
> This patch implements the functionality of jumping between the kexeced
> kernel and the original kernel.
> 

Hi,

I am just going through your patches and trying to understand it. Don't
understand many things. Asking is easy so here you go...

> 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.
> 

I need jumping back to restore a already hibernated kernel image? Can
you please tell little more about jumping back and why it is needed?

> To support jumping without reserving memory. One shadow backup page
> (source page) is allocated for each page used by new (kexeced) kernel
> (destination page). When do kexec_load, the image of new kernel is
> loaded into source pages, and before executing, the destination pages
> and the source pages are swapped, so the contents of destination pages
> are backupped. Before jumping to the new (kexeced) kernel and after
> jumping back to the original kernel, the destination pages and the
> source pages are swapped too.
> 

Ok, so due to swapping of source and destination pages first kernel's data
is still preserved.  How do I get the dynamic memory required for second
kernel boot (without writing first kernel's data)?

> A jump back protocol for kexec is defined and documented. It is an
> extension to ordinary function calling protocol. So, the facility
> provided by this patch can be used to call ordinary C function in real
> mode.
> 
> A set of flags for sys_kexec_load are added to control which state are
> saved/restored before/after real mode code executing. For example, you
> can specify the device state and FPU state are saved/restored
> before/after real mode code executing.
> 
> The states (exclude CPU state) save/restore code can be overridden
> based on the "command" parameter of kexec jump. Because more states
> need to be saved/restored by hibernating/resuming.
> 
> Signed-off-by: Huang Ying <ying.huang@intel.com>
> 
> ---
>  Documentation/i386/jump_back_protocol.txt |  103 ++++++++++++++
>  arch/powerpc/kernel/machine_kexec.c       |    2 
>  arch/ppc/kernel/machine_kexec.c           |    2 
>  arch/sh/kernel/machine_kexec.c            |    2 
>  arch/x86/kernel/machine_kexec_32.c        |   88 +++++++++---
>  arch/x86/kernel/machine_kexec_64.c        |    2 
>  arch/x86/kernel/relocate_kernel_32.S      |  214 +++++++++++++++++++++++++++---
>  include/asm-x86/kexec_32.h                |   39 ++++-
>  include/linux/kexec.h                     |   40 +++++
>  kernel/kexec.c                            |  188 ++++++++++++++++++++++++++
>  kernel/power/Kconfig                      |    2 
>  kernel/sys.c                              |   35 +++-
>  12 files changed, 648 insertions(+), 69 deletions(-)
> 
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -20,6 +20,7 @@
>  #include <asm/cpufeature.h>
>  #include <asm/desc.h>
>  #include <asm/system.h>
> +#include <asm/cacheflush.h>
>  
>  #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
>  static u32 kexec_pgd[1024] PAGE_ALIGNED;
> @@ -83,10 +84,14 @@ static void load_segments(void)
>   * reboot code buffer to allow us to avoid allocations
>   * later.
>   *
> - * Currently nothing.
> + * Turn off NX bit for control page.
>   */
>  int machine_kexec_prepare(struct kimage *image)
>  {
> +	if (nx_enabled) {
> +		change_page_attr(image->control_code_page, 1, PAGE_KERNEL_EXEC);
> +		global_flush_tlb();
> +	}
>  	return 0;
>  }
>  
> @@ -96,25 +101,59 @@ int machine_kexec_prepare(struct kimage 
>   */
>  void machine_kexec_cleanup(struct kimage *image)
>  {
> +	if (nx_enabled) {
> +		change_page_attr(image->control_code_page, 1, PAGE_KERNEL);
> +		global_flush_tlb();
> +	}
> +}
> +
> +void machine_kexec(struct kimage *image)
> +{
> +	machine_kexec_call(image, NULL, 0);
>  }
>  
>  /*
>   * Do not allocate memory (or fail in any way) in machine_kexec().
>   * We are past the point of no return, committed to rebooting now.
>   */
> -NORET_TYPE void machine_kexec(struct kimage *image)
> +int machine_kexec_vcall(struct kimage *image, unsigned long *ret,
> +			 unsigned int argc, va_list args)
>  {
>  	unsigned long page_list[PAGES_NR];
>  	void *control_page;
> +	asmlinkage NORET_TYPE void
> +		(*relocate_kernel_ptr)(unsigned long indirection_page,
> +				       unsigned long control_page,
> +				       unsigned long start_address,
> +				       unsigned int has_pae) ATTRIB_NORET;
>  
>  	/* Interrupts aren't acceptable while we reboot */
>  	local_irq_disable();
>  
>  	control_page = page_address(image->control_code_page);
> -	memcpy(control_page, relocate_kernel, PAGE_SIZE);
> +	memcpy(control_page, relocate_page, PAGE_SIZE/2);
> +	KCALL_MAGIC(control_page) = 0;
>  

Is 2K sufficient for all the code in relocate_kernel_32.S? What's the
current size?

> +	if (image->preserve_cpu) {
> +		unsigned int i;
> +		KCALL_MAGIC(control_page) = KCALL_MAGIC_NUMBER;
> +		KCALL_ARGC(control_page) = argc;
> +		for (i = 0; i < argc; i++)
> +			KCALL_ARGS(control_page)[i] = \
> +				va_arg(args, unsigned long);
> +
> +		if (kexec_call_save_cpu(control_page)) {
> +			image->start = KCALL_ENTRY(control_page);

Who fills the entry point at offset 0x200?


[..]
>  extern int machine_kexec_prepare(struct kimage *image);
>  extern void machine_kexec_cleanup(struct kimage *image);
>  extern asmlinkage long sys_kexec_load(unsigned long entry,
>  					unsigned long nr_segments,
>  					struct kexec_segment __user *segments,
>  					unsigned long flags);
> +extern int kexec_call(struct kimage *image, unsigned long *ret,
> +		      unsigned int argc, ...);

Who is using kexec_call(). I can't seem to locate the caller of it.


Thanks
Vivek

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