Re: [Xen-devel] crash on boot with 4.6.1 on fedora 24

[Juergen Gross <jgross@xxxxxxxx>]

On 10/05/16 17:35, Jan Beulich wrote:
>>>> On 10.05.16 at 17:19, <JGross@xxxxxxxx> wrote:
>> On 10/05/16 15:57, Jan Beulich wrote:
>>>>>> On 10.05.16 at 15:39, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>> I didn't finish unwrapping the stack yesterday. Here it is:
>>>>
>>>> setup_arch -> dmi_scan_machine -> dmi_walk_early -> early_ioremap
>>>
>>> Ah, that makes sense. Yet why would early_ioremap() involve an
>>> M2P lookup? As said, MMIO addresses shouldn't be subject to such
>>> lookups.
>>
>> early_ioremap()->
>>   __early_ioremap()->
>>     __early_set_fixmap()->
>>       set_pte()->
>>         xen_set_pte_init()->
>>           mask_rw_pte()->
>>             pte_pfn()->
>>               pte_val()->
>>                 xen_pte_val()->
>>                   pte_mfn_to_pfn()
> 
> Well, I understand (also from Boris' first reply) that's how it is,
> but not why it is so. I.e. the call flow above doesn't answer my
> question.

On x86 early_ioremap() and early_memremap() share a common sub-function
__early_ioremap(). This together with pvops requires a common set_pte()
implementation leading to the mfn validation in the end.


Juergen


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