[SOLVED] PCI passthrough fails after upgrade to Proxmox 7

[cmonty14]

Hello,
my initial Proxmox installation was 6.4 and I have enable PCI passthrough successfully.
This is my current /etc/default/grub:

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'


GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="Proxmox Virtual Environment"
GRUB_CMDLINE_LINUX_DEFAULT="intel_iommu=pt"
GRUB_CMDLINE_LINUX=""


# Disable os-prober, it might add menu entries for each guest
GRUB_DISABLE_OS_PROBER=true

However, after upgrading to Proxmox VE 7.0-8 I get this error message when starting a VM using PCI passthrough:
ERROR: IOMMU not present

Based on the Wiki page for PCI passthrough I have started some investigation I want to share here.

locadmin@maggie:~
$ cat /etc/modules
# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.


# Generated by sensors-detect on Fri Jun 11 00:21:41 2021
# Chip drivers
coretemp
ftsteutates
vfio
vfio_iommu_type1
vfio_pci
vfio_virqfd


locadmin@maggie:~
$ dmesg | grep 'remapping'
[    0.181526] DMAR-IR: Queued invalidation will be enabled to support x2apic and Intr-remapping.
[    0.184743] DMAR-IR: Enabled IRQ remapping in x2apic mode

locadmin@maggie:~
$ dmesg | grep 'IOMMU'
[    0.181523] DMAR-IR: IOAPIC id 2 under DRHD base  0xfed91000 IOMMU 1

locadmin@maggie:~
$ find /sys/kernel/iommu_groups/ -type l
locadmin@maggie:~


locadmin@maggie:~
$ uname -r
5.11.22-1-pve

In my opinion IOMMU PT mode (for IOMMU translation) is not working with the new kernel.

What is the root cause for this error?

THX

 

[leesteken]

pt is not a valid option for intel_iommu according to the documentation. Have you tried intel_iommu=on iommu=pt? This should enable intel_iommu and to not use iommu mapping (other than 1-to-1) for the host-only devices.

 

[cmonty14]

The root cause is a faulty /etc/default/grub entry.