IOMMU/PCI Passthrough to Windows with KVM

blackice8r

blackice8r

blackice8r

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I've looked around but couldn't see a thread on this.

a bit about myself:
I'm a linux noob but I would love to be able to run linux and power windows only when I want to play games.
I have a basic understanding of linux , have my own little ubuntu server (on an Intel NUC) for files (Drobo attached via USB) and Plex.
I manged to stick to linux on my desktop for about two months until I started gaming again..
I plan to get a new Ryzen system (my i5 3570k doesn't support IOMMU so I can't test KVM atm.)

Before I buy stuff I started doing some research and the results seem to vary.
Some claim this is working fine , with 2-5%max performance loss (Cpu -GPU) : https://forum.level1techs.com/t/play-games-in-windows-on-linux-pci-passthrough-quick-guide/108981
While other sources show mixed results: https://level1techs.com/video/ryzen-iommu-pcie-passthrough-works

The way I understand it, the problem seems to be the support on the motherboard. Not all manufacturers offer it, while others promise it in future BIOS updates.

I was wondering if anyone has a working KVM for gaming, any recommendations on a safe mobo to buy and advice on the performance loss ? (is it indeed just 2-5% ?)
 
This may help, Wendell is one of the few YT tech people who actually know what they are doing.


I know Gigabyte have sorted theirs (K5/7)

Bear in mind, you will need a AMD GPU to pass through, unless you have a NV Quodro based card
 
I used to have my primary W10 setup running this way. It does not have to be an AMD card, a while ago that was the case when I was running a 7970, but now Nvidia is good, I was using my 1070.

The key with Intel is that you need VT-d, not just VT-x, on both the motherboard and CPU. I was using X99 with a 5820k where I dedicated 8 cores.

I am no expert on the KVM/Linux side, I was using unRAID which makes it incredibly simple and does a whole lot more as a NAS type environment.

I have gone back to a dedicated machine but that was part due to USB pass-through being a bit of a pain, but mostly the fact I will probably watercool again and it does involve more faffing around than with a bare metal setup.

EDIT: I do still have a functional setup using an RX470 which needs some refinement. In the long run I want it to be a steam/moonlight streaming host.
 
The only reason that unRAID is the platform of choice is because of LTT. In this scenario it isn't suitable, nor does it make sense most of the time. The real challenge is ensuring compatibility with hardware. Once that's sussed out, setting up the virtual machine is straightforward.

Pick a Linux distribution that you're comfortable with for desktop usage (Fedora, Arch, Ubuntu, Debian, whatever), install Virtual Machine Manager (virt-manager, the de facto libvirt GUI), ensure that you have VT-x and VT-d enabled on an Intel platform (not sure what the name is on an AMD platform), and from there on it's very straight forward.
 
pete910 said:
This may help, Wendell is one of the few YT tech people who actually know what they are doing.


I know Gigabyte have sorted theirs (K5/7)

Bear in mind, you will need a AMD GPU to pass through, unless you have a NV Quodro based card
Click to expand...

Manny thanks for the replies guys!

I've seen that vid but never watched it fully, I've taken the time to do that today.
I understand more but the issues I feared remain:
- which motherboard provides the support ? The two he suggests are double the price of what I had in mind, I was going to get a B350 or a cheaper X370
- he claims gaming works, cool but whats the real performance loss? I see frame drops on the game tests he has running while recording.
Getting some games to work under linux is one thing, getting performance similar to Windows for AAA titles is a different thing.
- one thing I didn't think before this vid was - potentially - the need for a second Ethernet port on top of the two graphics (I was hoping to use an on board graphics and my gtx970)

Good to know there are workarounds to get Nvidia cards working.I have a gtx970 and I was hoping Vega would be the next upgrade but the news so far aren't that promising.
I don't know a great deal about unRAID but it looks like traditional virtualization, I'd prefer passthrough because in theory there is less performance loss.
The point with building a ryzen setup is to build a cost efficient pc (£200 mobo would defeat the point) that would compete on performance with an Intel setup. I plan to overclock at ~4ghz.

Anyone else has a working set-up?

I'm not in a huge rush with this just doing the research and find the potential very interesting
 
This is a really interesting thread, linux pass-through hadn't occurred to me before. I'm an intermediate (at best) with Linux and I'd like to run my primary desktop as Linux but I also like to game. This could give me the best of both worlds.

I have a skylake cpu already which I think supports everything I need. I'm going to fire up a linux live cd to confirm.

If it turns out I have everything I need I'll probably go with fedora 26 but arch linux is temping as I suspect i'd learn a lot more about Linux in general.
 
blackice8r said:
I don't know a great deal about unRAID but it looks like traditional virtualization, I'd prefer passthrough because in theory there is less performance loss.
Click to expand...

Full passthrough is supported in UnRaid under KVM. I run my Gaming rig as a Win10 VM with passed through 1070 and USB3 card. Works nicely, as well as also doubling up as a Usenet/Couch Potato/Sonaar downloader, Plex server, Calibre Server, Web server, File Server, NextCloud Server, Minecraft Server & Teamspeak Server. I did also, until recently, run a PfSense VM with passed through Dual Intel NIC which worked a treat too, just moved to a physical box so that I didn't lose internet when I mess with the server :)

Plenty cores left to run other VMs if I wish too.
 
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