Re: [Xen-devel] GPU passthrough issue when VM is configured with 4G memory

[Hanweidong <hanweidong@xxxxxxxxxx>]

> -----Original Message-----
> From: Gordan Bobic [mailto:gordan@xxxxxxxxxx]
> Sent: 2013å5æ22æ 23:18
> To: Hanweidong
> Cc: George Dunlap; Stefano Stabellini; xudong.hao@xxxxxxxxx;
> Yanqiangjun; Luonengjun; Wangzhenguo; Yangxiaowei; Gonglei (Arei);
> Anthony Perard; xen-devel@xxxxxxxxxxxxx; xiantao.zhang@xxxxxxxxx
> Subject: Re: [Xen-devel] GPU passthrough issue when VM is configured
> with 4G memory
> 
>  On Tue, 21 May 2013 04:09:25 +0000, Hanweidong <hanweidong@xxxxxxxxxx>
>  wrote:
> >> -----Original Message-----
> >> From: Gordan Bobic [mailto:gordan@xxxxxxxxxx]
> >> Sent: 2013å5æ21æ 2:43
> >> To: George Dunlap
> >> Cc: Hanweidong; Stefano Stabellini; xudong.hao@xxxxxxxxx;
> >> Yanqiangjun;
> >> Luonengjun; Wangzhenguo; Yangxiaowei; Gonglei (Arei); Anthony
> >> Perard;
> >> xen-devel@xxxxxxxxxxxxx; xiantao.zhang@xxxxxxxxx
> >> Subject: Re: [Xen-devel] GPU passthrough issue when VM is configured
> >> with 4G memory
> >>
> >> I'd also like to stress this is not only an issue for > 4GB of RAM
> >> in
> >> domU - I am seeing the issue with > 2GB of RAM in domU.
> >
> > What's the total mmio size of you domU?
> 
>  How can I find that out?

You can print mmio_total in pci_setup() in tools/firmware/hvmloader/pci.c.

> 
> > When RAM of domU overlaps
> > with pci_mem_start, hvmloader will relocate RAM, and it will cause
> > problem due to hvmloader and QEMU don't setup the memory layout
> > consistently. I suspect the mmio size of your domU is close to 2GB.
> > When you configured RAM > 2G, then RAM of your domU overlapped with
> > pci_mem_start, and resulted in failure.
> 
>  Is there a way to force a hole between, say, 2GB and 4GB explicitly
>  to avoid the PCI memory being clobbered?

No graceful way to do it, but you can hardcode it by modifying hvmloader and 
qemu code.

weidong

> 
>  Gordan
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