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

> -----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
> hole
> 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.

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