VirtualBox 7.2.0_beta1: cannot start vms if kernel 6.15.0 is compiled without CONFIG_KVM

[ceamac]

7.2.0_beta1 modules can be compiled against kernel 6.15.0, but if said kernel was configured without CONFIG_KVM, starting any vm fails with an error similar to this:

Failed to get a console object from the direct session (NS_ERROR_ABORT).

Result Code:
VBOX_E_VM_ERROR (0x80bb0003)
Component:
MachineWrap

This is new, it works fine with 6.14.x or lower.

CONFIG_KVM seems to be required at build time, not at run time.

[Vamp898]

When building the Kernel without KVM support again, i get the following error

depmod: WARNING: /lib/modules/6.15.0-Vamp898/misc/vboxdrv.ko needs unknown symbol preempt_notifier_inc
depmod: WARNING: /lib/modules/6.15.0-Vamp898/misc/vboxdrv.ko needs unknown symbol preempt_notifier_register
depmod: WARNING: /lib/modules/6.15.0-Vamp898/misc/vboxdrv.ko needs unknown symbol preempt_notifier_dec
depmod: WARNING: /lib/modules/6.15.0-Vamp898/misc/vboxdrv.ko needs unknown symbol preempt_notifier_unregister

That might be the key to this isuse.

[AlexanderEichner]

Looks like not having KVM enabled keeps CONFIG_PREEMPT_NOTIFIERS disabled which VirtualBox requires in order to work.

[Vamp898]

So is this something that needs to be reported to the Linux Kernel devs?

[AlexanderEichner]

No idea whether this will have any impact, as the preempt notifiers are only used by KVM and the Linux developers usually don't care too much about out of tree kernel modules.
What you can do however is just enable CONFIG_PREEMPT_NOTIFIERS in your kernel config without setting CONFIG_KVM.

[Vamp898]

It seems like this is no longer possible with Kernel 6.15 (at least not without manually putting it into the .config file. I tried it with make nconfig and the only way to do it seems to be to enable CONFIG_KVM).

So as of now, the "clean" way to get these settings is to enable CONFIG_KVM. Is there some way to let the build scripts check for these, or is this something that should end up in the manual and be handled on the distribution side?

[jospezial]

Symbol: KVM_COMMON [=y]                                                                                                                                                                                                                                                                      │  
  │ Type  : bool                                                                                                                                                                                                                                                                                 │  
  │ Defined at virt/kvm/Kconfig:4                                                                                                                                                                                                                                                                │  
  │ Selects: EVENTFD [=y] && INTERVAL_TREE [=y] && PREEMPT_NOTIFIERS [=y]                                                                                                                                                                                                                        │  
  │ Selected by [m]:                                                                                                                                                                                                                                                                             │  
  │   - KVM_X86 [=m] && VIRTUALIZATION [=y]

Symbol: KVM_X86 [=n]                                                                                                                                                                                                                                                                         │  
  │ Type  : tristate                                                                                                                                                                                                                                                                             │  
  │ Defined at arch/x86/kvm/Kconfig:20                                                                                                                                                                                                                                                           │  
  │   Depends on: VIRTUALIZATION [=y]                                                                                                                                                                                                                                                            │  
  │ Selects: KVM_COMMON [=n] && KVM_GENERIC_MMU_NOTIFIER [=n] && KVM_ELIDE_TLB_FLUSH_IF_YOUNG [=n] && KVM_MMU_LOCKLESS_AGING [=n] && HAVE_KVM_IRQCHIP [=n] && HAVE_KVM_PFNCACHE [=n] && HAVE_KVM_DIRTY_RING_TSO [=n] && HAVE_KVM_DIRTY_RING_ACQ_REL [=n] && HAVE_KVM_IRQ_BYPASS [=n] && HAVE_KVM │  
  │                                                                                                                                                                                                                                                                                              │  
  │

https://github.com/torvalds/linux/blob/9afe652958c3ee88f24df1e4a97f298afce89407/arch/x86/kvm/Kconfig#L21
KVM_INTEL or KVM_AMD needs to be enabled to get KVM_X86, KVM_COMMON and PREEMPT_NOTIFIERS.

But I think there was a problem that virtualbox could not use the CPU if KVM_AMD is loaded then.
That why I removed all kvm from my kernel config before.

[Vamp898]

That is true, you should not load the modules. But if you built them as a module, they should not autoload (unless you have something on your system that loads them)

[jospezial]

Enabling the kernel stuff solves also #37 .

they should not autoload (unless you have something on your system that loads them)

It does. I need to rmmod kvm_amd

[Vamp898]

This probably is distribution specific, I assume there is some mechanism in you distribution to prevent this, but you would have to consult the documentation of your distribution on how to prevent that

[jamescowens]

KVM is enabled on the 6.15.0 kernel I use. I have kvm_intel blacklisted and ensure the module is not loaded. So I don't think I am encountering this issue. The issue I reported in #13 remains.