[SOLVED] PCI passthrough on old hardware, IOMMU shows enabled, but can't use it

Kongolan

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Jan 20, 2022
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I'm pretty stuck here. I'm using old laptop hardware, with a i5-4200U, which does support VT-d and virtualization in BIOS, but i can't get it to work, while following the tutorial here: https://pve.proxmox.com/wiki/Pci_passthrough

When I try to add a PCI device to a VM, i get this message "No IOMMU detected, please activate it."

# dmesg | grep -e DMAR -e IOMMU [ 0.016855] ACPI: DMAR 0x000000009AFDB000 000088 (v01 ACRSYS ACRPRDCT 00000001 1025 00040000) [ 0.016894] ACPI: Reserving DMAR table memory at [mem 0x9afdb000-0x9afdb087] [ 0.037107] DMAR: IOMMU enabled [ 0.043883] DMAR: [Firmware Bug]: Your BIOS is broken; DMAR reported at address 0! # find /sys/kernel/iommu_groups/ -type l # ls -l /sys/kernel/iommu_groups/ total 0

It seems like IOMMU is enabled, but there are problems with the BIOS still, the iommu groups are empty.

Can someone please help me?
 
Last edited:

oguz

Proxmox Retired Staff
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Nov 19, 2018
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Kongolan

New Member
Jan 20, 2022
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You are correct, there were some options in the Chipset and the CPU BIOS options and I checked them both, but it seems in the end the i5-4200U doesn't support it. Even though all my efforts and settings did look like progress, in the end it wouldn't work.

Thanks for this, I really thought when the BIOS shows it, it would be possible, but it is not.

Also to note for some, this in the end lead me to this insight as well: https://ubuntuforums.org/showthread.php?t=2348650

"The check you did for IOMMU is not accurate, rather check this way as per Alex Williamson instructions. The dev for redhat working on KVM."

# dmesg | grep Virtual

"You need to see an output like below, if you don't see it then IOMMU is not enabled."

[ 0.428319] PCI-DMA: Intel(R) Virtualization Technology for Directed I/O
 

leesteken

Famous Member
May 31, 2020
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According to Intel, your CPU does not support VT-d, sorry. You did not specify your motherboard, so it is not clear whether it supports VT-d. Intel seems to be very specific about which CPU's and which motherboards are allowed to use VT-d for PCI(e) passthrough.
 

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