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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/18/2013 01:46 PM, Hanweidong wrote:
> > -----Original Message-----
> > From: George Dunlap [mailto:george.dunlap@xxxxxxxxxxxxx]
> > Sent: 2013å6æ18æ 20:21
> > To: Hanweidong
> > Cc: xen-devel@xxxxxxxxxxxxx; Ian Campbell; Ian Jackson; Stefano
> > Stabellini
> > Subject: Re: [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
> > > > 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.
> >
> > You mean to say, you've tried this approach before (relocating to a
> > 64-bit MMIO region) and it doesn't work?
> I didn't try this approach. I missed you want to map mmio to 64-bit space 
> instead of relocate memory. Currently only mmio size is larger than 512M 
> (PCI_MIN_BIG_BAR_SIZE) will be map to 64-bit space. So you need to change the 
> condition if you want to map smaller mmio to 64-bit space.
Ah, blast -- I forgot about that part.

Looks like the change will have to be bigger... :-(

 -George


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