Re: [PATCH v2] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

[Pierre Morel <pmorel@linux.ibm.com>]

On 8/19/22 23:10, Randy Dunlap wrote:
> 
> 
> On 8/19/22 05:29, 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>
>> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop interpretive execution")
>> Cc: <stable@vger.kernel.org>
> 
> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
> 
> Thanks.

Thanks Randy,

Regards,
Pierre


> 
>> ---
>>   arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
>>   arch/s390/kvm/pci.c              | 12 ++++++++----
>>   arch/s390/pci/Makefile           |  2 +-
>>   arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
>>   drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
>>   5 files changed, 32 insertions(+), 18 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..bb8c335d17b9 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;
>>   }
>> @@ -685,6 +687,8 @@ int kvm_s390_pci_init(void)
>>   void kvm_s390_pci_exit(void)
>>   {
>>   	mutex_destroy(&aift->aift_lock);
>> +	zpci_kvm_hook.kvm_register = NULL;
>> +	zpci_kvm_hook.kvm_unregister = NULL;
>>   
>>   	kfree(aift);
>>   }
>> diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
>> index bf557a1b789c..5ae31ca9dd44 100644
>> --- a/arch/s390/pci/Makefile
>> +++ b/arch/s390/pci/Makefile
>> @@ -5,5 +5,5 @@
>>   
>>   obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
>>   			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
>> -			   pci_bus.o
>> +			   pci_bus.o pci_kvm_hook.o
>>   obj-$(CONFIG_PCI_IOV)	+= pci_iov.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
>> --- /dev/null
>> +++ b/arch/s390/pci/pci_kvm_hook.c
>> @@ -0,0 +1,11 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * VFIO ZPCI devices support
>> + *
>> + * Copyright (C) IBM Corp. 2022.  All rights reserved.
>> + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
>> + */
>> +#include <linux/kvm_host.h>
>> +
>> +struct zpci_kvm_hook zpci_kvm_hook;
>> +EXPORT_SYMBOL_GPL(zpci_kvm_hook);
>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>> index e163aa9f6144..0cbdcd14f1c8 100644
>> --- a/drivers/vfio/pci/vfio_pci_zdev.c
>> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
>> @@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>>   	if (!vdev->vdev.kvm)
>>   		return 0;
>>   
>> -	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
>> +	if (zpci_kvm_hook.kvm_register)
>> +		return zpci_kvm_hook.kvm_register(zdev, vdev->vdev.kvm);
>> +
>> +	return -ENOENT;
>>   }
>>   
>>   void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>> @@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>>   	if (!zdev || !vdev->vdev.kvm)
>>   		return;
>>   
>> -	kvm_s390_pci_unregister_kvm(zdev);
>> +	if (zpci_kvm_hook.kvm_unregister)
>> +		zpci_kvm_hook.kvm_unregister(zdev);
>>   }
> 

-- 
Pierre Morel
IBM Lab Boeblingen