Proxmox GPU Passthrough

Level1Techs INBOX.deb
1

Hi, I’m just getting started with Proxmox and trying to understand and configure GPU passthrough following the wiki. When I run the following command

dmesg | grep -E “DMAR|IOMMU”

I get this output

[ 0.830081] pci 0000:00:00.2: AMD-Vi: IOMMU performance counters supported
[ 0.834179] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40
[ 0.834522] perf/amd_iommu: Detected AMD IOMMU #0 (2 banks, 4 counters/bank).
[ 15.526757] AMD-Vi: AMD IOMMUv2 loaded and initialized

Not this

PCIe ACS overrides enabled; This may allow non-IOMMU protected peer-to-peer DMA

Is there something i’m not setting correctly ?

Thanks

2

Not necessarily. Been a bit since I’ve set up a GPU passthrough, and I’m far from an expert at it, but if I recall, PCIe ACS Overrides are something you would configure in your grub file. It’s also something you really only want to enable as a last resort. If you don’t need PCIe ACS Overrides enabled to get the passthrough working, then it’s better not to.

Your first output looks pretty similar to what my own Proxmox server outputs:

[    0.323778] pci 0000:00:00.2: AMD-Vi: IOMMU performance counters supported
[    0.323802] pci 0000:40:00.2: AMD-Vi: IOMMU performance counters supported
[    0.325265] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40
[    0.325272] pci 0000:40:00.2: AMD-Vi: Found IOMMU cap 0x40
[    0.325829] perf/amd_iommu: Detected AMD IOMMU #0 (2 banks, 4 counters/bank).
[    0.325886] perf/amd_iommu: Detected AMD IOMMU #1 (2 banks, 4 counters/bank).
3

Thanks JackTL, i’ll investigate further. So my other thought is do I require a cable connected from the passthrough gpu to a seperate monitor ? At the moment I only have an ethernet cable from proxmox host to my desktop.

4

If its a headless gpu pass thru then video cable/monitor need be connected to the passed through gpu. You woul access this VM by rdp from another machine.
If the passthrough is not headless then yes it requires the traditional video cable/monitor connected.

5

As mentioned, ACS overrides should only be done if the motherboard/bios failed to properly separate things into their own groups.

Another thing that catches people off guard, is if you install proxmox on a ZFS root, then boot options have to be set with system-boot, instead of grub. Changes to grub options will be silently ignored: Host Bootloader - Proxmox VE

2 Likes
6

Thanks for the advice, I’m trying to setup a Headless gpu passthrough as the PVE is its own hardware and i’m accessing that from my desktop remotely.

7

Thanks for the advice

8

To further add to this confusion, as of v8.1 if you install onto a system that has secure boot enabled during install time, you will always get GRUB set as your bootloader even if you use ZFS on root.

9

That answers a question, thanks for that.

10

So for a headless setup, what do I have to connect to the passthough gpu ? At the moment I just have an ethernet connection from my PVE machine to my Desktop.