Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

[Pierre Morel]

On 8/19/22 09:14, Niklas Schnelle wrote:
> On Thu, 2022-08-18 at 18:46 +0200, Pierre Morel wrote:
> > We have a cross dependency between KVM and VFIO when using
> > s390 vfio_pci_zdev extensions for PCI passthrough
> > To be able to keep both subsystem modular we add a registering
> > hook inside the S390 core code.
> >
> > This fixes a build problem when VFIO is built-in and KVM is built
> > as a module.
> >
> > Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
>
> Please don't shorten the Fixes tag, the subject line is likely also
> checked by some automated tools. It's okay for this line to be over the
> column limit and checkpatch.pl --strict also accepts it.

OK

> > Cc: <stable@xxxxxxxxxxxxxxx>
> > ---
> >   arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
> >   arch/s390/kvm/pci.c              | 10 ++++++----
> >   arch/s390/pci/Makefile           |  2 ++
> >   arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
> >   drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
> >   5 files changed, 31 insertions(+), 17 deletions(-)
> >   create mode 100644 arch/s390/pci/pci_kvm_hook.c
> ---8<---
> >   
> >   	kvm_put_kvm(kvm);
> >   }
> > -EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
> >   
> >   void kvm_s390_pci_init_list(struct kvm *kvm)
> >   {
> > @@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
> >   
> >   	spin_lock_init(&aift->gait_lock);
> >   	mutex_init(&aift->aift_lock);
> > +	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
> > +	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
> >   
> >   	return 0;
> >   }
> > diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
> > index bf557a1b789c..c02dbfb415d9 100644
> > --- a/arch/s390/pci/Makefile
> > +++ b/arch/s390/pci/Makefile
> > @@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
> >   			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
> >   			   pci_bus.o
> >   obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
> > +
> > +obj-y += pci_kvm_hook.o
>
> I thought we wanted to compile this only for CONFIG_PCI?

Ah sorry, that is indeed what I understood with Matt but then I 
misunderstood your own answer from yesterday.
I change to
obj-$(CONFIG_PCI) += pci_kvm_hook.o

> > diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> > new file mode 100644
> > index 000000000000..ff34baf50a3e
> ---8<---

--
Pierre Morel
IBM Lab Boeblingen