Subject: Re: [PATCH v2 2/6] powerpc: kexec_file: Add buffer hand-over support for the next kernel

From: Thiago Jung Bauermann <[email-masked]>
Date: Mon, 22 Aug 2016 19:21:09 -0300

Am Montag, 22 August 2016, 15:22:00 schrieb Dave Young:
> On 08/22/16 at 12:38am, Thiago Jung Bauermann wrote:
> > Am Montag, 22 August 2016, 11:21:35 schrieb Dave Young:
> > > On 08/13/16 at 12:18am, Thiago Jung Bauermann wrote:
> > > > diff --git a/arch/powerpc/kernel/machine_kexec_64.c
> > > > b/arch/powerpc/kernel/machine_kexec_64.c index
> > > > a484a6346146..190c652e49b7 100644
> > > > --- a/arch/powerpc/kernel/machine_kexec_64.c
> > > > +++ b/arch/powerpc/kernel/machine_kexec_64.c
> > > > @@ -490,6 +490,60 @@ int arch_kimage_file_post_load_cleanup(struct
> > > > kimage *image)>
> > > > 
> > > >  	return image->fops->cleanup(image->image_loader_data);
> > > >  
> > > >  }
> > > > 
> > > > +bool kexec_can_hand_over_buffer(void)
> > > > +{
> > > > +	return true;
> > > > +}
> > > > +
> > > > +int arch_kexec_add_handover_buffer(struct kimage *image,
> > > > +				   unsigned long load_addr, unsigned 
long
> > 
> > size)
> > 
> > > > +{
> > > > +	image->arch.handover_buffer_addr = load_addr;
> > > > +	image->arch.handover_buffer_size = size;
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +int kexec_get_handover_buffer(void **addr, unsigned long *size)
> > > > +{
> > > > +	int ret;
> > > > +	u64 start_addr, end_addr;
> > > > +
> > > > +	ret = of_property_read_u64(of_chosen,
> > > > +				   "linux,kexec-handover-buffer-
start",
> > > > +				   &start_addr);
> > > > +	if (ret == -EINVAL)
> > > > +		return -ENOENT;
> > > > +	else if (ret)
> > > > +		return -EINVAL;
> > > > +
> > > > +	ret = of_property_read_u64(of_chosen,
> > > > "linux,kexec-handover-buffer-end", +
> > 
> > &end_addr);
> > 
> > > > +	if (ret == -EINVAL)
> > > > +		return -ENOENT;
> > > > +	else if (ret)
> > > > +		return -EINVAL;
> > > > +
> > > > +	*addr =  __va(start_addr);
> > > > +	/* -end is the first address after the buffer. */
> > > > +	*size = end_addr - start_addr;
> > > > +
> > > > +	return 0;
> > > > +}
> > > 
> > > This depends on dtb, so if IMA want to extend it to arches like x86 in
> > > the future you will have to think about other way to pass it.
> > > 
> > > How about think about a general way now?
> > 
> > The only general way I can think of is by adding a kernel command line
> > parameter which the first kernel would pass to the second kernel, but
> > IMHO that is ugly, because such parameter wouldn't be useful to a user,
> > and it would also be something that, from the perspective of the user,
> > would magically appear in the kernel command line of the second
> > kernel...
> Sorry I just brought up the question, actually I have no idea either.
> Maybe we have to do this with arch specific ways..

Actually, I don't think it's possible to avoid arch-specific code because 
the first kernel has to put the buffer memory region in a reserved memory 
map, and that is arch-specific.

On powerpc, this is done by adding it to the device tree memory reservation 
map. On x86, I believe this would be done added to the e820 map.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center