Re: [PATCH -mm] kexec jump -v9

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Thursday, 15 of May 2008, Eric W. Biederman wrote:
> "Huang, Ying" <ying.huang@intel.com> writes:
> 
> > This is a minimal patch with only the essential features. All
> > additional features are split out and can be discussed later. I think
> > it may be easier to get consensus on this minimal patch.
> 
> A minimal patch route sounds good.
> 
> 
> >   * 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 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, kexec_relocate_page, PAGE_SIZE/2);
> > +	KJUMP_MAGIC(control_page) = 0;
> >  
> > +	if (image->preserve_context) {
> > +		KJUMP_MAGIC(control_page) = KJUMP_MAGIC_NUMBER;
> > +		if (kexec_jump_save_cpu(control_page)) {
> > +			image->start = KJUMP_ENTRY(control_page);
> > +			return;
> 
> Tricky, and I expect unnecessary.
> We should be able to just have relocate_new_kernel return?
> 
> > +		}
> > +	}
> > +
> > +	relocate_kernel_ptr = control_page +
> > +		((void *)relocate_kernel - (void *)kexec_relocate_page);
> >  	page_list[PA_CONTROL_PAGE] = __pa(control_page);
> > -	page_list[VA_CONTROL_PAGE] = (unsigned long)relocate_kernel;
> > +	page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;
> >  	page_list[PA_PGD] = __pa(kexec_pgd);
> >  	page_list[VA_PGD] = (unsigned long)kexec_pgd;
> >  #ifdef CONFIG_X86_PAE
> > @@ -127,6 +148,7 @@ NORET_TYPE void machine_kexec(struct kim
> >  	page_list[VA_PTE_0] = (unsigned long)kexec_pte0;
> >  	page_list[PA_PTE_1] = __pa(kexec_pte1);
> >  	page_list[VA_PTE_1] = (unsigned long)kexec_pte1;
> > + page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page) << PAGE_SHIFT);
> >  
> >  	/* The segment registers are funny things, they have both a
> >  	 * visible and an invisible part.  Whenever the visible part is
> > @@ -145,8 +167,9 @@ NORET_TYPE void machine_kexec(struct kim
> >  	set_idt(phys_to_virt(0),0);
> >  
> >  	/* now call it */
> > -	relocate_kernel((unsigned long)image->head, (unsigned long)page_list,
> > -			image->start, cpu_has_pae);
> > +	relocate_kernel_ptr((unsigned long)image->head,
> > +			    (unsigned long)page_list,
> > +			    image->start, cpu_has_pae);
> >  }
> 
> 
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -301,18 +301,26 @@ EXPORT_SYMBOL_GPL(kernel_restart);
> >   *	Move into place and start executing a preloaded standalone
> >   *	executable.  If nothing was preloaded return an error.
> >   */
> > -static void kernel_kexec(void)
> > +static int kernel_kexec(void)
> >  {
> > +	int ret = -ENOSYS;
> >  #ifdef CONFIG_KEXEC
> > -	struct kimage *image;
> > -	image = xchg(&kexec_image, NULL);
> > -	if (!image)
> > -		return;
> > -	kernel_restart_prepare(NULL);
> > -	printk(KERN_EMERG "Starting new kernel\n");
> > -	machine_shutdown();
> > -	machine_kexec(image);
> > +	if (xchg(&kexec_lock, 1))
> > +		return -EBUSY;
> > +	if (!kexec_image) {
> > +		ret = -EINVAL;
> > +		goto unlock;
> > +	}
> > +	if (!kexec_image->preserve_context) {
> > +		kernel_restart_prepare(NULL);
> > +		printk(KERN_EMERG "Starting new kernel\n");
> > +		machine_shutdown();
> > +	}
> > +	ret = kexec_jump(kexec_image);
> > +unlock:
> > +	xchg(&kexec_lock, 0);
> >  #endif
> 
> Ugh.  No.  Not sharing the shutdown methods with reboot and
> the normal kexec path looks like a recipe for failure to me.
> 
> This looks like where we really need to have the conversation.
> What methods do we use to shutdown the system.
> 
> My take on the situation is this.  For proper handling we
> need driver device_detach and device_reattach methods.
> 
> With the following semantics.  The device_detach methods
> will disable DMA and place the hardware in a sane state
> from which the device driver can reclaim and reinitialize it,
> but the hardware will not be touched.
> 
> device_reattach reattaches the driver to the hardware.
> 
> So looking at this patch I see two very productive directions
> we can go.
> 1) A patch that just fixes up the kexec infrastructure code
>    so it implements the swap page and provides the kernel
>    reentry point.  And doesn't handle the upper layer
>    user interface portion.
> 
> 2) A patch that renames device_shutdown to device_detach.
>    And starts implementing the driver hooks needed from
>    a resumable kexec.
> 
> Then we have the question what do we do with devices in the
> kernel that don't have a device_reattach method, when we
> expect to come back from a kexec.  The two choices are:
> (a) fail the operations before we commit to anything.
> (b) hotunplug/hotreplug the device.
> 
> With respect to device methods.  I don't think any of
> the current power saving methods make sense.  Certainly
> nothing that prepares the way for using weird ACPI states.
> 
> I don't think there is not enough difference between
> device_detach and device_shutdown for us to maintain two
> separate methods, and that seems to place an unreasonable
> maintenance burden on device driver developers.

Well, it looks like we do similar things concurrently.  Please have a look 
here: http://kerneltrap.org/Linux/Separating_Suspend_and_Hibernation

Similar patches are in the Greg's tree already.

Thanks,
Rafael