Enabling KVM for AMD leads to boot hang

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Hello everyone,

I've been following Gentoo QEMU setup instructions.
I enabled "Virtualization -> KVM for AMD processors support" kernel option (I have Ryzen 7 9800X3D), as well as virtualization support (SVM Mode) in BIOS.
After building kernel and rebooting, the system hangs indefinitely at either "Setting system clock using the hardware clock" or "Activating swap devices" - seemingly random on each reboot.

What made no difference:
- Setting "KVM for AMD processors support" as built-in or module
- Enabling other kernel options suggested in the QEMU guide (Intel module and "Useful kernel configuration options")

I also checked that I have IOMMU enabled in BIOS and valid IOMMU groups according to this Arch Wiki guide.

Tried seeing if anything useful appears in /var/log/rc.log (I enabled logging in /etc/rc.conf), but it seems that writing starts after these failure points. The log file wasn't updated on unsuccessful boots - I checked its contents from my Windows installation after a failed Gentoo boot.

What can I do to debug this further? Has anyone seen a similar problem before?

Anon-E-moose · Posted: Sun Mar 09, 2025 9:06 pm Post subject:

Did you set IOMMU_DEFAULT_PASSTHROUGH
_________________
UM780, 6.12 zen kernel, gcc 13, openrc, wayland

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Tried this now, rebuilt kernel - still got stuck at "Activating swap devices".

Anon-E-moose · Posted: Sun Mar 09, 2025 9:48 pm Post subject:

sounds like not all of the kvm stuff is set or set right.

Best to have kvm as a separate module, but kvm_amd needs to also be set the same way (both modules or both built in)

wgetpaste your .config file and maybe something will show there.
_________________
UM780, 6.12 zen kernel, gcc 13, openrc, wayland

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Tried building everything as module, no difference.
Here's my .config - https://0x0.st/8SsR.txt

pietinger · Posted: Mon Mar 10, 2025 11:28 am Post subject:

MadWhiteCat,

first of all: Welcome to Gentoo Forums!

You miss two very important settings - please enable both:

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

pietinger, thanks a lot! Enabling those two options was the solution.
I will also check out the rest of the guides you linked for improved kernel settings.

pietinger · Posted: Mon Mar 10, 2025 2:31 pm Post subject:

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Update: Sorry for the confusion, it turns out I was loading the old kernel (grub-mkconfig replaced first entry which had new kernel with old one)... The boot hang is still there when I load my latest build.

pietinger · Posted: Mon Mar 10, 2025 3:07 pm Post subject:

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Here's a photo: https://ibb.co/PsSMmtv1
And here is my grub.cfg: https://0x0.st/8Sbn.cfg
"vmlinuz-6.13.6-gentoo-working" is the backup I've been loading instead of "vmlinuz-6.13.6-gentoo", again, sorry about that.

I also tried setting rc_parallel="YES" in rc.conf and got a lot of services timed out waiting for swap:
https://ibb.co/sJyq8z9f
https://ibb.co/fY2Wkwny

Disabling swap service gets the boot stuck on the next step - "Mounting local filesystems".

Anon-E-moose · Posted: Mon Mar 10, 2025 6:43 pm Post subject:

If I read the grub config properly you have

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Removed

Anon-E-moose · Posted: Mon Mar 10, 2025 7:41 pm Post subject:

Is this a desktop or laptop, model name/number if you know what it is off hand.

And if kvm is turned off does it boot?
_________________
UM780, 6.12 zen kernel, gcc 13, openrc, wayland

MadWhiteCat · n00b Joined: 09 Mar 2025 Posts: 8

Desktop PC. Hardware, if relevant: AMD Ryzen 7 9800X3D, NVIDIA 2080 Ti, MSI MAG X870E TOMAHAWK WIFI Motherboard. Gentoo on SSD.

And yes, simply disabling KVM makes it boot normally without changing any other options.