I have an AMD A4-5300 CPU with a motherboard that supports IOMMU and I am trying to enable IOMMU on my Gentoo Hardened 4.3.3-r4 kernel with the intention of using a graphics card on a KVM VM. According to this guide here, I'm supposed to recompile my kernel with a few provided options ("Support for DMA Remapping Devices", "Enable DMA Remapping Devices" and "PCI Stub driver"). However, "Support for DMA Remapping Devices" and "Enable DMA Remapping Devices" are absent from my kernel configuration.
I then searched the configuration for "remap" and tried enabling a number of options, which were CONFIG_IRQ_REMAP, CONFIG_DMAR_TABLE, CONFIG_IOMMU_SUPPORT, CONFIG_SWIOTLB and CONFIG_PCI_IOV. Then I recompiled my kernel with these options enabled, started my system with
amd_iommu=fullflush iommu=force on the kernel command line, and according to the aforementioned guide I checked if IOMMU was running on my system by looking for "AMD-Vi" on my kernel messages:
dmesg | grep AMD-Vi
Nothing shows up on my kernel log about AMD-Vi.
In addition, when I try to start a VM on virt-manager with an attached PCI device, I get a message that says "Error starting domain: unsupported configuration: host doesn't support passthrough of host PCI devices".
Pretty much everything I find is for Fedora, Ubuntu and Debian where IOMMU apparently Just Works out of the box. I don't believe it's a matter of my motherboard and CPU not supporting it, because my BIOS has an option for it, and because I remember being able a few years ago to run a VirtualBox VM with IOMMU on Debian (though I didn't follow up on it because I never thought at the moment that I required two graphic cards to use a GPU on a VM through IOMMU).
Here's what I have already tried but didn't work:
- Using the standard kernel instead of hardened.
- Enabling Device Drivers >> IOMMU Hardware Support, AMD IOMMU support, Support for Intel IOMMU using DMA Remapping Devices, Support for Interrupt Remapping and Bus options (PCI etc.) >> PCI Stub.
- Using the latest kernel, currently just upgraded to 4.4.8-hardened-r1.
This is the command line I'm using to start my kernel, with each parameter on a separate line for convenience:
root=/dev/ram0 crypt_root=/dev/disk/by-uuid/c1ce6456-4c6a-4a64-8027-5ec4fdc0f344 dolvm real_root=/dev/mapper/cryptgentoo-raiz rootfstype=jfs real_init=/sbin/init root_keydev=/dev/disk/by-partuuid/086194de-e476-4abb-82da-9744e6fb0257 root_key=luks-key.gpg keymap=la amd_iommu=on iommu=on
Am I still missing a kernel configuration option?
Update: Out of absent-mindedness I mistakenly issued
ps -ef | grep -i iommu, and look what I just found...
rockshooter ~ # ps -ef | grep iommu root 66 2 0 02:57 ? 00:00:00 [amd_iommu_v2]
If I see a kernel thread, I guess there might be a chance that I can get IOMMU running, it's just that my kernel isn't saying anything about it. It's just a wild guess... but I'm going to go ahead and try using it.