Re: [Xen-devel] Errors with Loading Xen at a Certain Address

[Julien Grall <julien.grall@arm.com>]

Hi,

On 03/10/2019 00:20, Brian Woods wrote:
> On Wed, Oct 02, 2019 at 02:22:49PM -0700, Brian Woods wrote:
>> On Wed, Oct 02, 2019 at 08:59:28PM +0100, Julien Grall wrote:
>>> Hi,
>>>
>>> On 10/2/19 7:56 PM, Brian Woods wrote:
>>>
>>> Hmmm, the first e-mail didn't land in my inbox directly (I have a filter
>>> send to a separate directory any e-mail I not CCed on). Did you BCC me by
>>> any change?
>> That's odd.  I know I copied your and Stefano's email addresses from the
>> MAINTAINERS file but under my sent emails it shows it has having no
>> CCs...  PEBCAK I guess.  My apologies.
>>>
>>> Let see try to troubleshoot it first :).
>>>
>>> Well, any attachment you send on the ML will store to each subscribers
>>> mailbox. I let you do the math here ;)
>>>
>>> So yeah, pastebin is always the preferred way when you have to send the full
>>> log.
>>>
>>> Thank you for the log. So that's probably not a double-init then.
>>>
>>> Looking back at the log, the values look quite sane. So I am not entirely
>>> sure what is happening.
>>>
>>> I would check that the frametable is correctly zeroed. You could add a print
>>> at the end of setup_frametable_mappings(...) to dump the count_info for the
>>> page. Something like:
>>>       mfn_to_page(_mfn(0x01533))->count_info;
>>>
>>> If it is correctly initialized, it should be zero.
>>>
>>> The next step would be to add a similar print in start_xen()
>>> (xen/arch/arm/setup.c) and see where the value is not 0 anymore.
>>>
>>> Cheers,
>>>
>>> -- 
>>> Julien Grall
>>
>> I'll go ahead add those and see if that leads to anything.
>>
>> -- 
>> Brian Woods
> 
> Ok, I added:
> 	printk("BW_DEBUG: 01 count_info=0x%016lx\n",
> 	    mfn_to_page(_mfn(0x01533))->count_info);
> In some places.  I'm not sure about some of the earlier ones (the ones
> before the UART is set up),  but all of the ones afterwards that
> actually get output are:
> 	BW_DEBUG: 11 count_info=0x0180000000000000
> 
> Is it worth trying to figure out where the printk buffer is and reading
> it really early on?
> 

If you haven't enable EARLY_PRINTK in Xen, then you may want to do it. This 
would help you to understand where the page->count_info is not zeroed.


Cheers,

-- 
Julien Grall

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