Re: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB

H. Peter Anvin
2008-03-05T17:33:38Z

Eduardo Habkost wrote:
>>>
>>> I am aware that it would take more work to tell all kernel code that it
>>> shouldn't look for BIOS data on this region when running as a domU guest,
>>> but it seems that it would be a better solution.
>>>
>> No, the right thing is for Xen to not try to map RAM in this area.
>
> Why? If the Xen host is telling us there is valid RAM in this area,
> why can't we use it?
>
> Existing Xen hosts use those physical address ranges for RAM. We can't
> fix this on the e820 map on the guest side without making otherwise-valid
> RAM unused.
>

x86 has a number of historical assumptions, both in kernel and in
userspace (consider dmidecode!) Trying to go against them is a losing
proposition, *AND* a headache for the maintainers, which will have to
consider "oh yes, and Xen does this dumb thing which goes against what
all the hardware does."

-hpa