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Re: [Qemu-discuss] GPU passthrough - 64-bit MMIO (with OVMF)

From: Thomas Lamprecht
Subject: Re: [Qemu-discuss] GPU passthrough - 64-bit MMIO (with OVMF)
Date: Tue, 23 Feb 2016 09:59:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

On 02/15/2016 09:58 AM, Thomas Lamprecht wrote:
> Hi all,
> I'm wondering if there is a possibility to pass through a big GPU like
> the NVIDIA Tesla K80 (with 24 GB ram).
> AFAIK, there is a problem with mapping that lot of memory which would
> need 64 bit MMIO
> (or "above 4G mapping" feature, like some firmware are calling it).
> So after some searching on the web I came to no clear answer and
> though simply asking here would be the best.
> I only found a post from about 2010 on the qemu-devel list [1] which
> stated that there isn't 64-bit MMIO support (yet),
> but also that it'd be useful. Was there any progress on this matter?
> If yes how could someone enable it (with OVMF?).
> How is the support for passing through such Hardware, or in other word
> has anybody achieved this?
> Maybe I should also note that smaller GPUs pass-through just fine.
> best regards,
> Thomas
> [1]
> https://lists.nongnu.org/archive/html/qemu-devel/2010-02/msg01106.html

For anyone wondering, or if someone stumbles upon this post,
as he run into problems when passing through a Tesla or similar graphic
card in the future,
qemu is fully to do this.
The limitation here comes from OVMF as Laszlo Ersek told me on a GitHub
issue I opened (thanks again).

Here's the quote [1]:
> QEMU definitely supports 64-bit MMIO for the x86_64 target.
> The PCI host bridge / root bridge driver that OVMF uses at the moment
> lacks support for 64-bit PCI MMIO however. This is a known limitation,
> and it should be resolved after OVMF is ported to the new, central PCI
> host bridge / root bridge driver in edk2. (It won't happen
> automatically with the port, but when the port is complete, it
> shouldn't take much work on top.)
> I started to work on that port recently, but ran into some issues with
> the central driver that OVMF should use. We've been discussing those
> topics recently on the mailing list, with @marcel-apf and @niruiyu .
> Please refer to these (sub)threads in the list archive:
> * http://thread.gmane.org/gmane.comp.bios.edk2.devel/6526/focus=6910
> * http://thread.gmane.org/gmane.comp.bios.edk2.devel/7382
> * http://thread.gmane.org/gmane.comp.bios.edk2.devel/7967
> * http://thread.gmane.org/gmane.comp.bios.edk2.devel/7969


[1] https://github.com/tianocore/edk2/issues/59#issuecomment-187226312

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