Re: [PATCH v5 01/31] vfio: Use file-based reference counting for KVM

[Steffen Eiden]

On Fri, Jul 31, 2026 at 03:08:29PM +0200, Steffen Eiden wrote:
> Replace manual module reference counting with file-based reference
> counting for KVM integration. Previously, VFIO used symbol_get() to
> obtain function pointers for kvm_get_kvm_safe() and kvm_put_kvm(),
> then manually tracked module references through these symbols. This
> approach required storing the put_kvm function pointer in each device
> and carefully managing symbol references.
> 
> Pass struct file pointers instead of struct kvm pointers throughout the
> VFIO-KVM interface. This leverages the kernel's existing file reference
> counting mechanism via get_file_active() and fput(), eliminating the
> need for manual module reference tracking. The file->private_data field
> provides access to the underlying struct kvm when needed.
> 
> This simplifies the code and removes all remaining externally exported
> symbols for KVM, paving the path for a second concurrent KVM module.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Steffen Eiden <seiden@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_page_track.h |  8 ++---
>  arch/x86/kvm/Makefile                 |  3 --
>  arch/x86/kvm/mmu/page_track.c         | 16 +++++----
>  drivers/s390/crypto/vfio_ap_ops.c     | 24 ++++++++++---
>  drivers/vfio/group.c                  |  2 +-
>  drivers/vfio/pci/vfio_pci_zdev.c      |  7 +++-
>  drivers/vfio/vfio.h                   | 10 +++---
>  drivers/vfio/vfio_main.c              | 49 ++++++---------------------
>  include/linux/kvm_host.h              |  2 ++
>  include/linux/vfio.h                  |  4 +--
>  virt/kvm/kvm_main.c                   | 23 ++++++++++---
>  virt/kvm/vfio.c                       |  8 ++---
>  12 files changed, 81 insertions(+), 75 deletions(-)

@sean: This is based on your draft in https://lore.kernel.org/all/adkFk3ZN4HJtpLA3@xxxxxxxxxx/
do you want another/more attribution? If yes which?

	Steffen