Re: [Xen-devel] Bug: Limitation of <=2GB RAM in domU persists with 4.3.0

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

Andrew Bobulsky <rulerof@xxxxxxxxx> wrote:
>On Thu, Jul 25, 2013 at 8:21 PM, Ian Campbell <ian.campbell@xxxxxxxxxx>
>wrote:
>> On Thu, 2013-07-25 at 23:23 +0100, Gordan Bobic wrote:
>>> Now, if I am understanding the basic nature of the problem
>correctly,
>>> this _could_ be worked around by ensuring that vBAR = pBAR since in
>that
>>> case there is no room for the mis-mapped memory overwrites to occur.
>Is
>>> that correct?
>>
>> AIUI (which is not very well...) it's not so much vBAR=pBAR but
>making
>> the guest e820 (memory map) have the same MMIO holes as the host so
>that
>> there can't be any clash between v- or p-BAR and RAM in the guest.
>>
>>> I guess I could test this easily enough by applying the vBAR = pBAR
>hack.
>>
>> Does the e820_host=1 option help? That might be PV only though, I
>can't
>> remember...
>
>Alas, yes.  The man pages list it under "PV Guest Specific Options":
>http://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html
>
>You got my hopes up! ;)
>
>Carry on!  I'll be sitting here metaphorically munching popcorn with
>anticipation :P
>
>-Andrew
>
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We could implement that for HVM guests too. But I am not sure about the 
consequences of this for migration (say you unplug the device  beforehand and 
then migrate to another host which has a different E820). That part requires a 
bit of pondering. 

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