Re: [XenARM] Question about booting parameter of Mini-OS for ARM

[Chen Baozi <baozich@xxxxxxxxx>]

On Mar 25, 2013, at 6:00 PM, Stefano Stabellini 
<Stefano.Stabellini@xxxxxxxxxxxxx> wrote:
> On Sun, 24 Mar 2013, Chen Baozi wrote:
>> Hi all,
>> 
>> I'm reading Mini-OS's codes and to estimate the amount of work porting it to
>> ARM (Ian's GSoC idea this year).
>> 
>> While Xen is booting Mini-OS on x86 platform, it passes the start_info_t to
>> the guest through ESI register. And Mini-OS would use this structure as the 
>> argument of start_kernel. However, I didn't see codes handle the
>> start_info_t on ARM side. Instead, I see a more standard protocal when
>> booting ARM's dom0, which follows linux kernel bootstrap rules:
>> 
>>      r0 = 0, r1 = machine nr, r2 = atags or dtb pointer
>> 
>> Does it mean that Xen for ARM does not use the start_info_t to pass
>> information when booting PV guest? 
>> Or did I miss something important?
> 
> That's right, we don't use start_info_t on ARM, in fact ARM guests are
> not exactly like x86 PV guests.
> The information present in the start_info page are either available via
> device tree or no used on ARM.

I noticed that in arch_domain_create() for arm there are codes
allocating xen heap pages for domain->shared_info:

arch_domain_create:
        if ((d->shared_info = alloc_xenheap_pages(0, 0)) == NULL)       

But it seems it is used nowhere and even not mapped by libxc:

int arch_setup_bootlate(struct xc_dom_image *dom)
{
        /* XXX
         *   map shared info
         *   map grant tables
         *   setup shared info
         */
        return 0;
}

So my question is what is the role of shared_info page in arm? 
And is there any relations between shared_info and start_info?

Thanks.

Chen Baozi

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