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



On Thu, 25 Jul 2013 21:15:10 -0400, 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

Now that is intereting - if this makes the memory holes the same between
the guest and the host, does it also implicitly vBAR=pBAR?

Gordan

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