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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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
> > 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?
> Georgeï
>
> 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.
Actually, did you have a way of testing this without actually having a 
real device to test it with?  That would help me sort things out much 
more quickly.
 -George

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