Re: [PATCH -mm 1/2] kexec jump -v12: kexec jump

[Huang Ying <ying.huang@intel.com>]

On Tue, 2008-07-08 at 10:50 -0400, Vivek Goyal wrote:
> On Mon, Jul 07, 2008 at 11:25:22AM +0800, Huang Ying wrote:
> > This patch provides an enhancement to kexec/kdump. It implements
> > the following features:
> > 
> > - Backup/restore memory used by the original kernel before/after
> >   kexec.
> > 
> > - Save/restore CPU state before/after kexec.
> > 
> 
> Hi Huang,
> 
> In general this patch set looks good enough to live in -mm and
> get some testing going.
> 
> To me, adding capability to return back to original kernel looks
> like a logical extension to kexec functionality.
> 
> Acked-by: Vivek Goyal <vgoyal@redhat.com>
> 
> Few minor comments inline.

Thank you very much!

> [..]
> > --- a/arch/x86/kernel/machine_kexec_32.c
> > +++ b/arch/x86/kernel/machine_kexec_32.c
> > @@ -22,6 +22,7 @@
> >  #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;
> > @@ -85,10 +86,12 @@ static void load_segments(void)
> >   * reboot code buffer to allow us to avoid allocations
> >   * later.
> >   *
> > - * Currently nothing.
> > + * Make control page executable.
> >   */
> >  int machine_kexec_prepare(struct kimage *image)
> >  {
> > +	if (nx_enabled)
> > +		set_pages_x(image->control_code_page, 1);
> >  	return 0;
> >  }
> >  
> > @@ -98,16 +101,24 @@ int machine_kexec_prepare(struct kimage 
> >   */
> >  void machine_kexec_cleanup(struct kimage *image)
> >  {
> > +	if (nx_enabled)
> > +		set_pages_nx(image->control_code_page, 1);
> >  }
> >  
> >  /*
> >   * 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)
> > +void machine_kexec(struct kimage *image)
> >  {
> >  	unsigned long page_list[PAGES_NR];
> >  	void *control_page;
> > +	asmlinkage unsigned long
> > +		(*relocate_kernel_ptr)(unsigned long indirection_page,
> > +				       unsigned long control_page,
> > +				       unsigned long start_address,
> > +				       unsigned int has_pae,
> > +				       unsigned int preserve_context);
> >  
> >  	tracer_disable();
> >  
> > @@ -115,10 +126,11 @@ NORET_TYPE void machine_kexec(struct kim
> >  	local_irq_disable();
> >  
> >  	control_page = page_address(image->control_code_page);
> > -	memcpy(control_page, relocate_kernel, PAGE_SIZE);
> > +	memcpy(control_page, relocate_kernel, PAGE_SIZE/2);
> >  
> 
> Is it possible to add either a compile time or run time check
> somewhere to make sure code in relocate_kernel.S does not exceed
> PAGE_SIZE/2.

OK, I will add it.

> [..]
> > --- a/kernel/kexec.c
> > +++ b/kernel/kexec.c
> > @@ -24,6 +24,8 @@
> >  #include <linux/utsrelease.h>
> >  #include <linux/utsname.h>
> >  #include <linux/numa.h>
> > +#include <linux/suspend.h>
> > +#include <linux/device.h>
> >  
> >  #include <asm/page.h>
> >  #include <asm/uaccess.h>
> > @@ -242,6 +244,12 @@ static int kimage_normal_alloc(struct ki
> >  		goto out;
> >  	}
> >  
> > +	image->swap_page = kimage_alloc_control_pages(image, 0);
> > +	if (!image->swap_page) {
> > +		printk(KERN_ERR "Could not allocate swap buffer\n");
> > +		goto out;
> > +	}
> > +
> >  	result = 0;
> >   out:
> >  	if (result == 0)
> > @@ -986,6 +994,8 @@ asmlinkage long sys_kexec_load(unsigned 
> >  		if (result)
> >  			goto out;
> >  
> > +		if (flags & KEXEC_PRESERVE_CONTEXT)
> > +			image->preserve_context = 1;
> >  		result = machine_kexec_prepare(image);
> >  		if (result)
> >  			goto out;
> > @@ -1411,3 +1421,50 @@ static int __init crash_save_vmcoreinfo_
> >  }
> >  
> >  module_init(crash_save_vmcoreinfo_init)
> > +
> > +/**
> > + *	kernel_kexec - reboot the system
> > + *
> > + *	Move into place and start executing a preloaded standalone
> > + *	executable.  If nothing was preloaded return an error.
> > + */
> > +int kernel_kexec(void)
> > +{
> > +	int error = 0;
> > +
> > +	if (xchg(&kexec_lock, 1))
> > +		return -EBUSY;
> > +	if (!kexec_image) {
> > +		error = -EINVAL;
> > +		goto Unlock;
> > +	}
> > +
> > +	if (kexec_image->preserve_context) {
> > +#ifdef CONFIG_KEXEC_JUMP
> > +		local_irq_disable();
> > +		save_processor_state();
> > +#endif
> > +	} else {
> > +		blocking_notifier_call_chain(&reboot_notifier_list,
> > +					     SYS_RESTART, NULL);
> > +		system_state = SYSTEM_RESTART;
> > +		device_shutdown();
> > +		sysdev_shutdown();
> > +		printk(KERN_EMERG "Starting new kernel\n");
> > +		machine_shutdown();
> 
> All the above code was part of kernel_restart_prepare(), can't we just
> make that function non-static and use that?

OK, I will do that.

> [..]
> > --- a/arch/x86/kernel/relocate_kernel_32.S
> > +++ b/arch/x86/kernel/relocate_kernel_32.S
> > @@ -20,11 +20,44 @@
> >  #define PAGE_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
> >  #define PAE_PGD_ATTR (_PAGE_PRESENT)
> >  
> > +/* control_page + PAGE_SIZE/2 ~ control_page + PAGE_SIZE * 3/4 are
> > + * used to save some data for jumping back
> > + */
> > +#define DATA(offset)		(PAGE_SIZE/2+(offset))
> > +
> > +/* Minimal CPU state */
> > +#define ESP			DATA(0x0)
> > +#define CR0			DATA(0x4)
> > +#define CR3			DATA(0x8)
> > +#define CR4			DATA(0xc)
> > +
> > +/* other data */
> > +#define CP_VA_CONTROL_PAGE	DATA(0x10)
> > +#define CP_PA_PGD		DATA(0x14)
> > +#define CP_PA_SWAP_PAGE		DATA(0x18)
> > +#define CP_PA_BACKUP_PAGES_MAP	DATA(0x1c)
> > +
> 
> In general, this assembly piece of code is getting bigger and its
> difficult to read it now. I think we should at-least pull out the page
> table setup code into C. Somebody had posted a patch to do that. Don't
> know what happened to that. Anyway, this is a separate issue and is on
> wish list.

In fact, that patch was posted by me. I will re-post that patch.

Best Regards,
Huang Ying



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