Re: [Xen-devel] [PATCH] xen: find a better location for the real-mode trampoline

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.12.12 at 14:22, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> Il 18/12/2012 14:07, Jan Beulich ha scritto:
>>>>> On 30.11.12 at 09:33, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>>>>>> On 29.11.12 at 18:34, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>>>> On some machines, the location at 0x40e does not point to the beginning
>>>> of the EBDA.  Rather, it points to the beginning of the BIOS-reserved
>>>> area of the EBDA, while the option ROMs place their data below that
>>>> segment.
>>>>
>>>> For this reason, 0x413 is actually a better source than 0x40e to get
>>>> the location of the real-mode trampoline.  But it is even better to
>>>> fetch the information from the multiboot structure, where the boot
>>>> loader has placed the data for us already.
>>>
>>> I think if anything we really should make this a minimum calculation
>>> of all three (sanity checked) values, rather than throwing the other
>>> sources out. It's just not certain enough that we can trust all
>>> multiboot implementations.
>> 
>> I never saw a response from you on this one - were you
>> intending to follow up, or did you (silently) expect us to sort
>> this out?
> 
> No, just busy.  I agree that checking all three is best.  However, there
> is at least one known case where 0x40e doesn't work, so 0x413 and
> multiboot should be enough.

Can you provide more detail about this specific case? In
particular, what value 0x40e in fact has there?

Jan


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