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

Pierre Morel
2022-08-18T20:55:20Z

On 8/18/22 22:38, Matthew Rosato wrote:
> On 8/18/22 12:46 PM, 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@infradead.org>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
>> Cc: <stable@vger.kernel.org>
>> ---
>> 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
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index f39092e0ceaa..b1e98a9ed152 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>> #define __KVM_HAVE_ARCH_VM_FREE
>> void kvm_arch_free_vm(struct kvm *kvm);
>>
>> -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>> -#else
>> -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
>> - struct kvm *kvm)
>> -{
>> - return -EPERM;
>> -}
>> -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
>> -#endif
>> +struct zpci_kvm_hook {
>> + int (*kvm_register)(void *opaque, struct kvm *kvm);
>> + void (*kvm_unregister)(void *opaque);
>> +};
>> +
>> +extern struct zpci_kvm_hook zpci_kvm_hook;
>>
>> #endif
>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>> index 4946fb7757d6..22c025538323 100644
>> --- a/arch/s390/kvm/pci.c
>> +++ b/arch/s390/kvm/pci.c
>> @@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
>> * available, enable them and let userspace indicate whether or not they will
>> * be used (specify SHM bit to disable).
>> */
>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>> +static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
>> {
>> + struct zpci_dev *zdev = opaque;
>> int rc;
>>
>> if (!zdev)
>> @@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>> kvm_put_kvm(kvm);
>> return rc;
>> }
>> -EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
>>
>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>> +static void kvm_s390_pci_unregister_kvm(void *opaque)
>> {
>> + struct zpci_dev *zdev = opaque;
>> struct kvm *kvm;
>>
>> if (!zdev)
>> @@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>>
>> 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;
>> }
>
> You should also set these to NULL in kvm_s390_pci_exit (which is called from kvm_arch_exit). In practice, the kvm module would need to be loaded again before we have a nonzero vdev->vdev.kvm so it should never be an issue - but we should clean up anyway when the module is removed.
>
> With that change:
>
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
>

Yes indeed, will do.
Thanks

Pierre

--
Pierre Morel
IBM Lab Boeblingen