Re: [PATCH 1/4 -mm] kexec based hibernation -v7 : kexec jump
From: Vivek Goyal
Date: Mon Dec 10 2007 - 14:57:17 EST
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@xxxxxxxxx>
>
> ---
> 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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