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

[Sean Christopherson <seanjc@google.com>]

On Fri, Jul 31, 2026, Steffen Eiden wrote:
> 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@nvidia.com>
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
> > ---
> >  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@google.com/
> do you want another/more attribution? 

No preference.  Do whatever feels right to you, you'll know better than me how
much of the final code came from me.  If you want to give me a Co-developed-by,
here's my:

  Signed-off-by: Sean Christopherson <seanjc@google.com>