Re: [PATCH 0/3] KVM, vfio: remove exported KVM symbols

[Alex Williamson]

On Tue,  7 Apr 2026 20:01:04 +0200
Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:

> KVM right now exports three symbols for the whole kernel to manage
> the reference count of "struct kvm"; these are used by VFIO just to
> keep the "struct kvm" alive.  This can mostly be replaced
> by inlines, and in fact the entire definition of struct kvm can be
> made opaque to VFIO.
> 
> Besides the cleanup of removing the sort-of-deprecated symbol_get() and
> the bidirectional dependency between KVM and VFIO, this is useful for
> the recently posted support for Arm VMs on s390.  In that scenario each
> KVM implementation module wants to have its own copy of kvm_put_kvm()
> in order to call the "right" kvm_destroy_vm().  With multiple modules,
> VFIO has no way to do a symbol_get() from the right module.
> 
> With this series, that problem is gone because kvm_put_kvm dispatches
> through a function pointer, set by whichever implementation creates the VM.
> The main issue is that symbol_get() was implicitly taking a reference
> to the KVM module, and that has to be preserved.  This is the purpose
> of patch 1.
> 
> Thanks,
> 
> Paolo
> 
> Paolo Bonzini (3):
>   VFIO: take reference to the KVM module
>   KVM, vfio: remove symbol_get(kvm_get_kvm_safe) from vfio
>   KVM, vfio: remove symbol_get(kvm_put_kvm) from vfio
> 
>  arch/x86/kvm/mmu/tdp_mmu.c |  2 +-
>  arch/x86/kvm/vmx/nested.h  |  4 +--
>  drivers/vfio/device_cdev.c |  2 +-
>  drivers/vfio/group.c       |  5 ++--
>  drivers/vfio/vfio.h        | 15 +++++++----
>  drivers/vfio/vfio_main.c   | 51 ++++++++++++++------------------------
>  include/linux/kvm_host.h   |  9 +++----
>  include/linux/kvm_types.h  | 30 ++++++++++++++++++++++
>  include/linux/vfio.h       |  4 +--
>  virt/kvm/kvm_main.c        | 34 ++++++-------------------
>  virt/kvm/vfio.c            |  4 +--
>  11 files changed, 80 insertions(+), 80 deletions(-)
> 

Looks clean.

Acked-by: Alex Williamson <alex@xxxxxxxxxxx>