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Re: [Xen-devel] [PATCH] libxl, hvmloader: Don't relocate memory for MMIO hole

On 06/18/2013 01:18 PM, Hanweidong wrote:
-----Original Message-----
From: George Dunlap [mailto:george.dunlap@xxxxxxxxxxxxx]
Sent: 2013å6æ18æ 0:49
To: George Dunlap
Cc: xen-devel@xxxxxxxxxxxxx; Ian Campbell; Ian Jackson; Stefano
Stabellini; Hanweidong
Subject: Re: [PATCH] libxl,hvmloader: Don't relocate memory for MMIO

On 17/06/13 17:43, George Dunlap wrote:
At the moment, qemu-xen can't handle memory being relocated by
hvmloader.  This may happen if a device with a large enough memory
region is passed through to the guest.  At the moment, if this
happens, then at some point in the future qemu will crash and the
domain will hang.  (qemu-traditional is fine.)

It's too late in the release to do a proper fix, so we try to do
damage control.

hvmloader already has mechanisms to relocate memory to 64-bit space
if it can't make a big enough MMIO hole.  By default this is 2GiB; if
we just refuse to make the hole bigger if it will overlap with guest
memory, then this codepath will be taken by default.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
CC: Hanweidong <hanweidong@xxxxxxxxxx>

Unfortunatley, I don't have an easy way to test this, as all of the
devices on my system are far smaller than 256MiB.

Weidong, could you give this patch a try and see if it works for you?


I don't have a system in hand to test it today. I try to have a test tomorrow. 
In my experience, when it's prevented to relocate memory for MMIO hole by your 
patch, windows guest will crash (blue screen) and linux guest will hang with a 
blank display.

You mean to say, you've tried this approach before (relocating to a 64-bit MMIO region) and it doesn't work?

BTW, don't try this patch -- it probably won't compile. I've got a v2 coming up to use instead.


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