[SOLVED] Could not access KVM kernel module

[Lumpy Gravy]

Hi,
Yesterday everyhink was working fine but this morning, my hypervisor was off and when I started it, the VM on it refused to boot.
Here's the error message:

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qemu-system-x86_64: -accel kvm: Could not access KVM kernel module: No such file or directory
qemu-system-x86_64: -accel kvm: failed to initialize kvm: No such file or director

I found nothing in dmesg:

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# dmesg | grep kvm
[    0.342023] kvm_amd: TSC scaling supported
[    0.342030] kvm_amd: Nested Virtualization enabled
[    0.342032] kvm_amd: Nested Paging enabled
[    0.342035] kvm_amd: LBR virtualization supported

The kvm module is builtin:

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# cat /usr/src/linux/.config | grep KVM
CONFIG_KVM_COMMON=y
CONFIG_HAVE_KVM_PFNCACHE=y
CONFIG_HAVE_KVM_IRQCHIP=y
CONFIG_HAVE_KVM_IRQ_ROUTING=y
CONFIG_HAVE_KVM_DIRTY_RING=y
CONFIG_HAVE_KVM_DIRTY_RING_TSO=y
CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL=y
CONFIG_KVM_MMIO=y
CONFIG_KVM_ASYNC_PF=y
CONFIG_HAVE_KVM_MSI=y
CONFIG_HAVE_KVM_READONLY_MEM=y
CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT=y
CONFIG_KVM_VFIO=y
CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=y
CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY=y
CONFIG_KVM_COMPAT=y
CONFIG_HAVE_KVM_IRQ_BYPASS=y
CONFIG_HAVE_KVM_NO_POLL=y
CONFIG_KVM_XFER_TO_GUEST_WORK=y
CONFIG_KVM_GENERIC_HARDWARE_ENABLING=y
CONFIG_KVM_GENERIC_MMU_NOTIFIER=y
CONFIG_KVM_X86=y
CONFIG_KVM=y
CONFIG_KVM_WERROR=y
# CONFIG_KVM_INTEL is not set
CONFIG_KVM_AMD=y
CONFIG_KVM_SMM=y
CONFIG_KVM_HYPERV=y
# CONFIG_KVM_XEN is not set
CONFIG_KVM_MAX_NR_VCPUS=1024

What could I do ?
Thanks.

[alamahant]

Plz do

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if [ ! -e /dev/kvm ]; then
    echo "Creating /dev/kvm..."
    sudo mknod /dev/kvm c 10 232
    sudo chmod 660 /dev/kvm
    sudo chown root:kvm /dev/kvm 2>/dev/null
else
    echo "/dev/kvm already exists."
fi

And if indeed it was absent and after being created qemu works maybe invoke it at machine booting
or maybe better creating a tmpfile

/etc/tmpfiles.d/kvm.conf

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c /dev/kvm 0660 root kvm - 10:232

[Hu]

The kvm device ought to be created automatically. Manual creation is interesting to detect if the absence is the only problem, but if it is absent on its own, even after a reboot, deeper investigation is warranted.

[Lumpy Gravy]

Plz do

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if [ ! -e /dev/kvm ]; then
    echo "Creating /dev/kvm..."
    sudo mknod /dev/kvm c 10 232
    sudo chmod 660 /dev/kvm
    sudo chown root:kvm /dev/kvm 2>/dev/null
else
    echo "/dev/kvm already exists."
fi

/dev/kvm already exists.

Well it seems to be here.

[Lumpy Gravy]

Maybe it's a hardware probem, it was running on an old FX-6300, so I tried to move the VM on another hypervisor but with intel CPU so I ran into an "Illegal instruction" error while trying to chroot.
Same thing on yet another hypervisor with AMD this time but a Ryzen 5 2600.
I will have to rebuild the VM but it's a mail server, if it can't run again, how could I retrieve the mails ?

[Hu]

Although hardware errors can happen, I would rule out other things first. Usually, hardware errors are catastrophic, rather than disabling one feature and leaving everything else intact.

Start by posting kern.log, ideally with enough history to see both the bad boot where KVM does not work, and the last good boot where it did.

If you can't start the system, then mount its drive as a data drive in a working system and copy the content out that way.

[Lumpy Gravy]

I don't see anything suspicious.

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Mar 24 14:25:14 TC-14 kernel: kvm_amd: TSC scaling supported
Mar 24 14:25:14 TC-14 kernel: kvm_amd: Nested Virtualization enabled
Mar 24 14:25:14 TC-14 kernel: kvm_amd: Nested Paging enabled
Mar 24 14:25:14 TC-14 kernel: kvm_amd: LBR virtualization supported
...
Nov 27 07:47:18 TC-14 kernel: kvm_amd: TSC scaling supported
Nov 27 07:47:18 TC-14 kernel: kvm_amd: Nested Virtualization enabled
Nov 27 07:47:18 TC-14 kernel: kvm_amd: Nested Paging enabled
Nov 27 07:47:18 TC-14 kernel: kvm_amd: LBR virtualization supported

but I'm not sure what I'm looking for.
Maybe it's a permission thing ?

[Lumpy Gravy]

It was a permission thing !
My user was not in the kvm group, before, I just needed to be in the libvirt group if I remember well.