[PATCH] vfio-pci/zdev: require KVM to be built-in

[PATCH] vfio-pci/zdev: require KVM to be built-in

[Randy Dunlap]

Fix build errors when CONFIG_KVM=m:

s390-linux-ld: drivers/vfio/pci/vfio_pci_zdev.o: in function `vfio_pci_zdev_open_device':
vfio_pci_zdev.c:(.text+0x242): undefined reference to `kvm_s390_pci_register_kvm'
s390-linux-ld: drivers/vfio/pci/vfio_pci_zdev.o: in function `vfio_pci_zdev_close_device':
vfio_pci_zdev.c:(.text+0x296): undefined reference to `kvm_s390_pci_unregister_kvm'

Having a bool Kconfig symbol depend on a tristate symbol can often
lead to problems like this.

Fixes: 8061d1c31f1a ("vfio-pci/zdev: add open/close device hooks")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Matthew Rosato <mjrosato@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Pierre Morel <pmorel@linux.ibm.com>
Cc: Eric Farman <farman@linux.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: kvm@vger.kernel.org
---
 drivers/vfio/pci/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -46,7 +46,7 @@ endif
 
 config VFIO_PCI_ZDEV_KVM
 	bool "VFIO PCI extensions for s390x KVM passthrough"
-	depends on S390 && KVM
+	depends on S390 && KVM=y
 	default y
 	help
 	  Support s390x-specific extensions to enable support for enhancements

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Pierre Morel]

Thank you Randy for this good catch.
However forcing KVM to be include statically in the kernel when using 
VFIO_PCI extensions is not a good solution for us I think.

I suggest we better do something like:

----

diff --git a/arch/s390/include/asm/kvm_host.h 
b/arch/s390/include/asm/kvm_host.h
index 6287a843e8bc..1733339cc4eb 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -1038,7 +1038,7 @@ 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
+#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || 
defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
  int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
  void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
  #else
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index f9d0c908e738..bbc375b028ef 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -45,9 +45,9 @@ config VFIO_PCI_IGD
  endif

  config VFIO_PCI_ZDEV_KVM
-       bool "VFIO PCI extensions for s390x KVM passthrough"
+       def_tristate y
+       prompt "VFIO PCI extensions for s390x KVM passthrough"
         depends on S390 && KVM
-       default y
         help
           Support s390x-specific extensions to enable support for 
enhancements
           to KVM passthrough capabilities, such as interpretive 
execution of

----

What do you think? It seems to me it solves the problem, what do you think?

Regards,
Pierre

On 8/14/22 23:51, Randy Dunlap wrote:
> Fix build errors when CONFIG_KVM=m:
> 
> s390-linux-ld: drivers/vfio/pci/vfio_pci_zdev.o: in function `vfio_pci_zdev_open_device':
> vfio_pci_zdev.c:(.text+0x242): undefined reference to `kvm_s390_pci_register_kvm'
> s390-linux-ld: drivers/vfio/pci/vfio_pci_zdev.o: in function `vfio_pci_zdev_close_device':
> vfio_pci_zdev.c:(.text+0x296): undefined reference to `kvm_s390_pci_unregister_kvm'
> 
> Having a bool Kconfig symbol depend on a tristate symbol can often
> lead to problems like this.
> 
> Fixes: 8061d1c31f1a ("vfio-pci/zdev: add open/close device hooks")
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> Reported-by: kernel test robot <lkp@intel.com>
> Cc: Matthew Rosato <mjrosato@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Pierre Morel <pmorel@linux.ibm.com>
> Cc: Eric Farman <farman@linux.ibm.com>
> Cc: linux-s390@vger.kernel.org
> Cc: kvm@vger.kernel.org
> ---
>   drivers/vfio/pci/Kconfig |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -46,7 +46,7 @@ endif
>   
>   config VFIO_PCI_ZDEV_KVM
>   	bool "VFIO PCI extensions for s390x KVM passthrough"
> -	depends on S390 && KVM
> +	depends on S390 && KVM=y
>   	default y
>   	help
>   	  Support s390x-specific extensions to enable support for enhancements
> 

-- 
Pierre Morel
IBM Lab Boeblingen

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Randy Dunlap]

Hi--

On 8/15/22 02:43, Pierre Morel wrote:
> Thank you Randy for this good catch.
> However forcing KVM to be include statically in the kernel when using VFIO_PCI extensions is not a good solution for us I think.
> 
> I suggest we better do something like:
> 
> ----
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 6287a843e8bc..1733339cc4eb 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -1038,7 +1038,7 @@ 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
> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)

This all looks good except for the line above.
It should be:

#if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)

Thanks.


>  int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>  void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>  #else
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index f9d0c908e738..bbc375b028ef 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -45,9 +45,9 @@ config VFIO_PCI_IGD
>  endif
> 
>  config VFIO_PCI_ZDEV_KVM
> -       bool "VFIO PCI extensions for s390x KVM passthrough"
> +       def_tristate y
> +       prompt "VFIO PCI extensions for s390x KVM passthrough"
>         depends on S390 && KVM
> -       default y
>         help
>           Support s390x-specific extensions to enable support for enhancements
>           to KVM passthrough capabilities, such as interpretive execution of
> 
> ----
> 
> What do you think? It seems to me it solves the problem, what do you think?
> 
> Regards,
> Pierre


-- 
~Randy

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Pierre Morel]

On 8/16/22 08:04, Randy Dunlap wrote:
> Hi--
> 
> On 8/15/22 02:43, Pierre Morel wrote:
>> Thank you Randy for this good catch.
>> However forcing KVM to be include statically in the kernel when using VFIO_PCI extensions is not a good solution for us I think.
>>
>> I suggest we better do something like:
>>
>> ----
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 6287a843e8bc..1733339cc4eb 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -1038,7 +1038,7 @@ 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
>> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
> 
> This all looks good except for the line above.
> It should be:
> 
> #if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
> 
> Thanks.

Yes, better, thanks.
How do we do? Should I repost it with reported-by you or do you want to 
post it?

Pierre


> 
> 
>>   int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>>   void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>>   #else
>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
>> index f9d0c908e738..bbc375b028ef 100644
>> --- a/drivers/vfio/pci/Kconfig
>> +++ b/drivers/vfio/pci/Kconfig
>> @@ -45,9 +45,9 @@ config VFIO_PCI_IGD
>>   endif
>>
>>   config VFIO_PCI_ZDEV_KVM
>> -       bool "VFIO PCI extensions for s390x KVM passthrough"
>> +       def_tristate y
>> +       prompt "VFIO PCI extensions for s390x KVM passthrough"
>>          depends on S390 && KVM
>> -       default y
>>          help
>>            Support s390x-specific extensions to enable support for enhancements
>>            to KVM passthrough capabilities, such as interpretive execution of
>>
>> ----
>>
>> What do you think? It seems to me it solves the problem, what do you think?
>>
>> Regards,
>> Pierre
> 
> 

-- 
Pierre Morel
IBM Lab Boeblingen

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Pierre Morel]

Randy,

I need to provide the correction patch rapidly.
Without answer I will propose the patch.

Regards,
Pierre

On 8/16/22 09:55, Pierre Morel wrote:
> 
> 
> On 8/16/22 08:04, Randy Dunlap wrote:
>> Hi--
>>
>> On 8/15/22 02:43, Pierre Morel wrote:
>>> Thank you Randy for this good catch.
>>> However forcing KVM to be include statically in the kernel when using 
>>> VFIO_PCI extensions is not a good solution for us I think.
>>>
>>> I suggest we better do something like:
>>>
>>> ----
>>>
>>> diff --git a/arch/s390/include/asm/kvm_host.h 
>>> b/arch/s390/include/asm/kvm_host.h
>>> index 6287a843e8bc..1733339cc4eb 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
>>> @@ -1038,7 +1038,7 @@ 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
>>> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || 
>>> defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
>>
>> This all looks good except for the line above.
>> It should be:
>>
>> #if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
>>
>> Thanks.
> 
> Yes, better, thanks.
> How do we do? Should I repost it with reported-by you or do you want to 
> post it?
> 
> Pierre
> 
> 
>>
>>
>>>   int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>>>   void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>>>   #else
>>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
>>> index f9d0c908e738..bbc375b028ef 100644
>>> --- a/drivers/vfio/pci/Kconfig
>>> +++ b/drivers/vfio/pci/Kconfig
>>> @@ -45,9 +45,9 @@ config VFIO_PCI_IGD
>>>   endif
>>>
>>>   config VFIO_PCI_ZDEV_KVM
>>> -       bool "VFIO PCI extensions for s390x KVM passthrough"
>>> +       def_tristate y
>>> +       prompt "VFIO PCI extensions for s390x KVM passthrough"
>>>          depends on S390 && KVM
>>> -       default y
>>>          help
>>>            Support s390x-specific extensions to enable support for 
>>> enhancements
>>>            to KVM passthrough capabilities, such as interpretive 
>>> execution of
>>>
>>> ----
>>>
>>> What do you think? It seems to me it solves the problem, what do you 
>>> think?
>>>
>>> Regards,
>>> Pierre
>>
>>
> 

-- 
Pierre Morel
IBM Lab Boeblingen

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Randy Dunlap]

On 8/16/22 06:47, Pierre Morel wrote:
> Randy,
> 
> I need to provide the correction patch rapidly.
> Without answer I will propose the patch.
> 
> Regards,
> Pierre

Please go ahead with it.
Thanks.

> 
> On 8/16/22 09:55, Pierre Morel wrote:
>>
>>
>> On 8/16/22 08:04, Randy Dunlap wrote:
>>> Hi--
>>>
>>> On 8/15/22 02:43, Pierre Morel wrote:
>>>> Thank you Randy for this good catch.
>>>> However forcing KVM to be include statically in the kernel when using VFIO_PCI extensions is not a good solution for us I think.
>>>>
>>>> I suggest we better do something like:
>>>>
>>>> ----
>>>>
>>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>>> index 6287a843e8bc..1733339cc4eb 100644
>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>> @@ -1038,7 +1038,7 @@ 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
>>>> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
>>>
>>> This all looks good except for the line above.
>>> It should be:
>>>
>>> #if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
>>>
>>> Thanks.
>>
>> Yes, better, thanks.
>> How do we do? Should I repost it with reported-by you or do you want to post it?
>>
>> Pierre
>>
>>
>>>
>>>
>>>>   int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>>>>   void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>>>>   #else
>>>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
>>>> index f9d0c908e738..bbc375b028ef 100644
>>>> --- a/drivers/vfio/pci/Kconfig
>>>> +++ b/drivers/vfio/pci/Kconfig
>>>> @@ -45,9 +45,9 @@ config VFIO_PCI_IGD
>>>>   endif
>>>>
>>>>   config VFIO_PCI_ZDEV_KVM
>>>> -       bool "VFIO PCI extensions for s390x KVM passthrough"
>>>> +       def_tristate y
>>>> +       prompt "VFIO PCI extensions for s390x KVM passthrough"
>>>>          depends on S390 && KVM
>>>> -       default y
>>>>          help
>>>>            Support s390x-specific extensions to enable support for enhancements
>>>>            to KVM passthrough capabilities, such as interpretive execution of
>>>>
>>>> ----
>>>>
>>>> What do you think? It seems to me it solves the problem, what do you think?
>>>>
>>>> Regards,
>>>> Pierre
>>>
>>>
>>
> 

-- 
~Randy

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Matthew Rosato]

On 8/16/22 3:55 AM, Pierre Morel wrote:
> 
> 
> On 8/16/22 08:04, Randy Dunlap wrote:
>> Hi--
>>
>> On 8/15/22 02:43, Pierre Morel wrote:
>>> Thank you Randy for this good catch.
>>> However forcing KVM to be include statically in the kernel when using VFIO_PCI extensions is not a good solution for us I think.
>>>
>>> I suggest we better do something like:
>>>
>>> ----
>>>
>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>> index 6287a843e8bc..1733339cc4eb 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
>>> @@ -1038,7 +1038,7 @@ 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
>>> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
>>
>> This all looks good except for the line above.
>> It should be:
>>
>> #if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
>>
>> Thanks.
> 
> Yes, better, thanks.
> How do we do? Should I repost it with reported-by you or do you want to post it?
> 
> Pierre

Thanks for looking into this while I was away.

I think the issue is not just CONFIG_KVM=m && CONFIG_VFIO_PCI_ZDEV_KVM=y -- it also requires CONFIG_VFIO_PCI=y && CONFIG_VFIO_PCI_CORE=y.  This combination results in building in vfio_pci (which tries to link the calls to kvm_s390_pci_register_kvm and kvm_s390_pci_unregister_kvm which is not built in).

However... this tristate + IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) check in kvm_host.h will not solve the issue.  Rather, due to the #ifdef CONFIG_VFIO_PCI_ZDEV_KVM in include/linux/vfio_pci_core.h, this change will just cause us to never call kvm_s390_pci_register_kvm or kvm_s390_pci_unregister_kvm when CONFIG_VFIO_PCI_ZDEV_KVM=m, effectively treating CONFIG_VFIO_PCI_ZDEV_KVM=m as a 'n' and we don't get the zdev kvm extensions, which I don't think was the intent.

I'm still thinking & am open to other ideas, but one solution to avoiding building in KVM would be to go back to using symbol_get for these 2 interfaces (kvm_s390_pci_register_kvm and kvm_s390_pci_unregister_kvm) as was done in a prior version of this series like virt/kvm/vfio.c does and otherwise leave CONFIG_VFIO_PCI_ZDEV_KVM as-is. 

diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
index e163aa9f6144..09c2758134c7 100644
--- a/drivers/vfio/pci/vfio_pci_zdev.c
+++ b/drivers/vfio/pci/vfio_pci_zdev.c
@@ -144,6 +144,8 @@ int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
 int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
 {
        struct zpci_dev *zdev = to_zpci(vdev->pdev);
+       int (*fn)(struct zpci_dev *zdev, struct kvm *kvm);
+       int rc;
 
        if (!zdev)
                return -ENODEV;
@@ -151,15 +153,30 @@ 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);
+       fn = symbol_get(kvm_s390_pci_register_kvm);
+       if (!fn)
+               return -EPERM;
+
+       rc = fn(zdev, vdev->vdev.kvm);
+
+       symbol_put(kvm_s390_pci_register_kvm);
+
+       return rc;
 }
 
 void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
 {
        struct zpci_dev *zdev = to_zpci(vdev->pdev);
+       void (*fn)(struct zpci_dev *zdev);
 
        if (!zdev || !vdev->vdev.kvm)
                return;
 
-       kvm_s390_pci_unregister_kvm(zdev);
+       fn = symbol_get(kvm_s390_pci_unregister_kvm);
+       if (!fn)
+               return;
+
+       fn(zdev);
+
+       symbol_put(kvm_s390_pci_unregister_kvm);
 }

Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

[Pierre Morel]

On 8/16/22 21:46, Matthew Rosato wrote:
> On 8/16/22 3:55 AM, Pierre Morel wrote:
>>
>>
>> On 8/16/22 08:04, Randy Dunlap wrote:
>>> Hi--
>>>
>>> On 8/15/22 02:43, Pierre Morel wrote:
>>>> Thank you Randy for this good catch.
>>>> However forcing KVM to be include statically in the kernel when using VFIO_PCI extensions is not a good solution for us I think.
>>>>
>>>> I suggest we better do something like:
>>>>
>>>> ----
>>>>
>>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>>> index 6287a843e8bc..1733339cc4eb 100644
>>>> --- a/arch/s390/include/asm/kvm_host.h
>>>> +++ b/arch/s390/include/asm/kvm_host.h
>>>> @@ -1038,7 +1038,7 @@ 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
>>>> +#if defined(CONFIG_VFIO_PCI_ZDEV_KVM) || defined(CONFIG_VFIO_PCI_ZDEV_KVM_MODULE)
>>>
>>> This all looks good except for the line above.
>>> It should be:
>>>
>>> #if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
>>>
>>> Thanks.
>>
>> Yes, better, thanks.
>> How do we do? Should I repost it with reported-by you or do you want to post it?
>>
>> Pierre
> 
> Thanks for looking into this while I was away.
> 
> I think the issue is not just CONFIG_KVM=m && CONFIG_VFIO_PCI_ZDEV_KVM=y -- it also requires CONFIG_VFIO_PCI=y && CONFIG_VFIO_PCI_CORE=y.  This combination results in building in vfio_pci (which tries to link the calls to kvm_s390_pci_register_kvm and kvm_s390_pci_unregister_kvm which is not built in).
> 
> However... this tristate + IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) check in kvm_host.h will not solve the issue.  Rather, due to the #ifdef CONFIG_VFIO_PCI_ZDEV_KVM in include/linux/vfio_pci_core.h, this change will just cause us to never call kvm_s390_pci_register_kvm or kvm_s390_pci_unregister_kvm when CONFIG_VFIO_PCI_ZDEV_KVM=m, effectively treating CONFIG_VFIO_PCI_ZDEV_KVM=m as a 'n' and we don't get the zdev kvm extensions, which I don't think was the intent.
> 
> I'm still thinking & am open to other ideas, but one solution to avoiding building in KVM would be to go back to using symbol_get for these 2 interfaces (kvm_s390_pci_register_kvm and kvm_s390_pci_unregister_kvm) as was done in a prior version of this series like virt/kvm/vfio.c does and otherwise leave CONFIG_VFIO_PCI_ZDEV_KVM as-is.
> 
> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index e163aa9f6144..09c2758134c7 100644
> --- a/drivers/vfio/pci/vfio_pci_zdev.c
> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> @@ -144,6 +144,8 @@ int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
>   int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>   {
>          struct zpci_dev *zdev = to_zpci(vdev->pdev);
> +       int (*fn)(struct zpci_dev *zdev, struct kvm *kvm);
> +       int rc;
>   
>          if (!zdev)
>                  return -ENODEV;
> @@ -151,15 +153,30 @@ 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);
> +       fn = symbol_get(kvm_s390_pci_register_kvm);
> +       if (!fn)
> +               return -EPERM;
> +
> +       rc = fn(zdev, vdev->vdev.kvm);
> +
> +       symbol_put(kvm_s390_pci_register_kvm);
> +
> +       return rc;
>   }
>   
>   void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>   {
>          struct zpci_dev *zdev = to_zpci(vdev->pdev);
> +       void (*fn)(struct zpci_dev *zdev);
>   
>          if (!zdev || !vdev->vdev.kvm)
>                  return;
>   
> -       kvm_s390_pci_unregister_kvm(zdev);
> +       fn = symbol_get(kvm_s390_pci_unregister_kvm);
> +       if (!fn)
> +               return;
> +
> +       fn(zdev);
> +
> +       symbol_put(kvm_s390_pci_unregister_kvm);
>   }
> 
> 


Hello Matt,

In between I came to another solution that seems to satisfy the 
dependencies.
Still need to check that the functionality is still intact :)

I send you the proposition as a reply.

Regards,
Pierre




-- 
Pierre Morel
IBM Lab Boeblingen

[PATCH] KVM: s390: pci: VFIO_PCI ZDEV configuration fix

[Pierre Morel]

Fixing configuration for VFIO PCI interpretation.

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..")
Fixes: c435c54639aa5 ("vfio/pci: introduce CONFIG_VFIO_PCI_ZDEV_KVM..")
Cc: <stable@vger.kernel.org>
---
 arch/s390/include/asm/kvm_host.h | 9 ---------
 arch/s390/kvm/Makefile           | 2 +-
 arch/s390/kvm/pci.c              | 4 ++--
 drivers/vfio/pci/Kconfig         | 4 ++--
 include/linux/vfio_pci_core.h    | 2 +-
 5 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index f39092e0ceaa..f6cf961731af 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -1038,16 +1038,7 @@ 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
 
 #endif
diff --git a/arch/s390/kvm/Makefile b/arch/s390/kvm/Makefile
index 02217fb4ae10..be36afcfd6ff 100644
--- a/arch/s390/kvm/Makefile
+++ b/arch/s390/kvm/Makefile
@@ -9,6 +9,6 @@ ccflags-y := -Ivirt/kvm -Iarch/s390/kvm
 
 kvm-y += kvm-s390.o intercept.o interrupt.o priv.o sigp.o
 kvm-y += diag.o gaccess.o guestdbg.o vsie.o pv.o
+kvm-y += pci.o
 
-kvm-$(CONFIG_VFIO_PCI_ZDEV_KVM) += pci.o
 obj-$(CONFIG_KVM) += kvm.o
diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index 4946fb7757d6..cf8ab72a2109 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -435,7 +435,7 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
 {
 	int rc;
 
-	if (!zdev)
+	if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) || !zdev)
 		return -EINVAL;
 
 	mutex_lock(&zdev->kzdev_lock);
@@ -516,7 +516,7 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
 {
 	struct kvm *kvm;
 
-	if (!zdev)
+	if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) || !zdev)
 		return;
 
 	mutex_lock(&zdev->kzdev_lock);
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index f9d0c908e738..bbc375b028ef 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -45,9 +45,9 @@ config VFIO_PCI_IGD
 endif
 
 config VFIO_PCI_ZDEV_KVM
-	bool "VFIO PCI extensions for s390x KVM passthrough"
+	def_tristate y
+	prompt "VFIO PCI extensions for s390x KVM passthrough"
 	depends on S390 && KVM
-	default y
 	help
 	  Support s390x-specific extensions to enable support for enhancements
 	  to KVM passthrough capabilities, such as interpretive execution of
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 5579ece4347b..7db3bb8129b1 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -205,7 +205,7 @@ static inline int vfio_pci_igd_init(struct vfio_pci_core_device *vdev)
 }
 #endif
 
-#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
+#if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
 int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
 				struct vfio_info_cap *caps);
 int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev);
-- 
2.31.1

Re: [PATCH] KVM: s390: pci: VFIO_PCI ZDEV configuration fix

[Matthew Rosato]

On 8/16/22 4:28 PM, Pierre Morel wrote:
> Fixing configuration for VFIO PCI interpretation.
> 
> 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..")
> Fixes: c435c54639aa5 ("vfio/pci: introduce CONFIG_VFIO_PCI_ZDEV_KVM..")
> Cc: <stable@vger.kernel.org>
> ---
>  arch/s390/include/asm/kvm_host.h | 9 ---------
>  arch/s390/kvm/Makefile           | 2 +-
>  arch/s390/kvm/pci.c              | 4 ++--
>  drivers/vfio/pci/Kconfig         | 4 ++--
>  include/linux/vfio_pci_core.h    | 2 +-
>  5 files changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index f39092e0ceaa..f6cf961731af 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -1038,16 +1038,7 @@ 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
>  
>  #endif
> diff --git a/arch/s390/kvm/Makefile b/arch/s390/kvm/Makefile
> index 02217fb4ae10..be36afcfd6ff 100644
> --- a/arch/s390/kvm/Makefile
> +++ b/arch/s390/kvm/Makefile
> @@ -9,6 +9,6 @@ ccflags-y := -Ivirt/kvm -Iarch/s390/kvm
>  
>  kvm-y += kvm-s390.o intercept.o interrupt.o priv.o sigp.o
>  kvm-y += diag.o gaccess.o guestdbg.o vsie.o pv.o
> +kvm-y += pci.o
>  
> -kvm-$(CONFIG_VFIO_PCI_ZDEV_KVM) += pci.o

You would need to switch this to CONFIG_PCI at least, else we get build errors with CONFIG_PCI=n.

>  obj-$(CONFIG_KVM) += kvm.o
> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> index 4946fb7757d6..cf8ab72a2109 100644
> --- a/arch/s390/kvm/pci.c
> +++ b/arch/s390/kvm/pci.c
> @@ -435,7 +435,7 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>  {
>  	int rc;
>  
> -	if (!zdev)
> +	if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) || !zdev)
>  		return -EINVAL;
>  
>  	mutex_lock(&zdev->kzdev_lock);
> @@ -516,7 +516,7 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>  {
>  	struct kvm *kvm;
>  
> -	if (!zdev)
> +	if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) || !zdev)
>  		return;
>  
>  	mutex_lock(&zdev->kzdev_lock);
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index f9d0c908e738..bbc375b028ef 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -45,9 +45,9 @@ config VFIO_PCI_IGD
>  endif
>  
>  config VFIO_PCI_ZDEV_KVM
> -	bool "VFIO PCI extensions for s390x KVM passthrough"
> +	def_tristate y
> +	prompt "VFIO PCI extensions for s390x KVM passthrough"
>  	depends on S390 && KVM
> -	default y
>  	help
>  	  Support s390x-specific extensions to enable support for enhancements
>  	  to KVM passthrough capabilities, such as interpretive execution of
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index 5579ece4347b..7db3bb8129b1 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -205,7 +205,7 @@ static inline int vfio_pci_igd_init(struct vfio_pci_core_device *vdev)
>  }
>  #endif
>  
> -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
> +#if IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)
>  int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
>  				struct vfio_info_cap *caps);
>  int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev);

This still doesn't seem quite right...  I tried some variations:

1)
CONFIG_KVM=m
CONFIG_VFIO_PCI_CORE=m
CONFIG_VFIO_PCI=m
CONFIG_VFIO_PCI_ZDEV_KVM=m

compiles, works with a small change:

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index f054d0360a75..99734e135420 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -25,7 +25,7 @@ struct user_struct {
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
        defined(CONFIG_NET) || defined(CONFIG_IO_URING) || \
-       defined(CONFIG_VFIO_PCI_ZDEV_KVM)
+       IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)


2)
CONFIG_KVM=y
CONFIG_VFIO_PCI_CORE=m
CONFIG_VFIO_PCI=m
CONFIG_VFIO_PCI_ZDEV_KVM=m

compiles, works with above user.h change

3)
CONFIG_KVM=y
CONFIG_VFIO_PCI_CORE=y
CONFIG_VFIO_PCI=y
CONFIG_VFIO_PCI_ZDEV_KVM=y

compiles, works with above user.h change

4)
CONFIG_KVM=m
CONFIG_VFIO_PCI_CORE=y
CONFIG_VFIO_PCI=y
CONFIG_VFIO_PCI_ZDEV_KVM=m

fails with:

ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_enable':
/usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:320: undefined reference to `vfio_pci_zdev_open_device'
ld: /usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:349: undefined reference to `vfio_pci_zdev_close_device'
ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_disable':
/usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:428: undefined reference to `vfio_pci_zdev_close_device'
ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_ioctl':
/usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:712: undefined reference to `vfio_pci_info_zdev_add_caps'


5)
CONFIG_KVM=m
CONFIG_VFIO_PCI_CORE=y
CONFIG_VFIO_PCI=y
CONFIG_VFIO_PCI_ZDEV_KVM=y

This forces CONFIG_VFIO_PCI_ZDEV_KVM to 'm' and fails as above.

Re: [PATCH] KVM: s390: pci: VFIO_PCI ZDEV configuration fix

[Pierre Morel]

On 8/17/22 00:15, Matthew Rosato wrote:
> On 8/16/22 4:28 PM, Pierre Morel wrote:
>> Fixing configuration for VFIO PCI interpretation.
>>

> 4)
> CONFIG_KVM=m
> CONFIG_VFIO_PCI_CORE=y
> CONFIG_VFIO_PCI=y
> CONFIG_VFIO_PCI_ZDEV_KVM=m
> 
> fails with:
> 
> ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_enable':
> /usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:320: undefined reference to `vfio_pci_zdev_open_device'
> ld: /usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:349: undefined reference to `vfio_pci_zdev_close_device'
> ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_disable':
> /usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:428: undefined reference to `vfio_pci_zdev_close_device'
> ld: drivers/vfio/pci/vfio_pci_core.o: in function `vfio_pci_core_ioctl':
> /usr/src/linux/drivers/vfio/pci/vfio_pci_core.c:712: undefined reference to `vfio_pci_info_zdev_add_caps'
> 
> 
> 5)
> CONFIG_KVM=m
> CONFIG_VFIO_PCI_CORE=y
> CONFIG_VFIO_PCI=y
> CONFIG_VFIO_PCI_ZDEV_KVM=y
> 
> This forces CONFIG_VFIO_PCI_ZDEV_KVM to 'm' and fails as above.
> 
> 
> 

yes right
I was really too stupid yesterday
I think you are right and you should go as you proposed or use some 
pointer hook inside S390 to register with KVM.

-- 
Pierre Morel
IBM Lab Boeblingen

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

[Pierre Morel]

We have a cross dependency between KVM and VFIO.
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 or excluded.

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..8312ed9d1937 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 kvm_register_hook {
+	int (*kvm_register)(void *opaque, struct kvm *kvm);
+	void (*kvm_unregister)(void *opaque);
+};
+
+extern struct kvm_register_hook kvm_pci_hook;
 
 #endif
diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index 4946fb7757d6..e173fce64c4f 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);
+	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
+	kvm_pci_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
diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
new file mode 100644
index 000000000000..9d8799b72dbf
--- /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 kvm_register_hook kvm_pci_hook;
+EXPORT_SYMBOL_GPL(kvm_pci_hook);
diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
index e163aa9f6144..3b7a707e2fe5 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 (kvm_pci_hook.kvm_register)
+		return kvm_pci_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 (kvm_pci_hook.kvm_unregister)
+		return kvm_pci_hook.kvm_unregister(zdev);
 }
-- 
2.31.1

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

[Matthew Rosato]

On 8/18/22 6:23 AM, Pierre Morel wrote:
> We have a cross dependency between KVM and VFIO.

maybe add something like '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 or excluded.

s/or excluded//

There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.

> 
> 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..8312ed9d1937 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 kvm_register_hook {

Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
> +	void (*kvm_unregister)(void *opaque);
> +};
> +
> +extern struct kvm_register_hook kvm_pci_hook;

Nit: kvm_zpci_hook ?

>  
>  #endif
> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> index 4946fb7757d6..e173fce64c4f 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);
> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
> +	kvm_pci_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 guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.

> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> new file mode 100644
> index 000000000000..9d8799b72dbf
> --- /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 kvm_register_hook kvm_pci_hook;
> +EXPORT_SYMBOL_GPL(kvm_pci_hook);

Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?

I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index e163aa9f6144..3b7a707e2fe5 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 (kvm_pci_hook.kvm_register)
> +		return kvm_pci_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 (kvm_pci_hook.kvm_unregister)
> +		return kvm_pci_hook.kvm_unregister(zdev);

No need for the return here, this is a void function calling a void function.


Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!

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

[Pierre Morel]

On 8/18/22 15:33, Matthew Rosato wrote:
> On 8/18/22 6:23 AM, Pierre Morel wrote:
>> We have a cross dependency between KVM and VFIO.
> 
> maybe add something like '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 or excluded.
> 
> s/or excluded//
> 
> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.

OK

> 
>>
>> 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..8312ed9d1937 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 kvm_register_hook {
> 
> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

OK


> 
>> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
>> +	void (*kvm_unregister)(void *opaque);
>> +};
>> +
>> +extern struct kvm_register_hook kvm_pci_hook;
> 
> Nit: kvm_zpci_hook ?

OK too,

> 
>>   
>>   #endif
>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>> index 4946fb7757d6..e173fce64c4f 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);
>> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
>> +	kvm_pci_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 guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.

Right,CONFIG_PCI is a bool so we can put the hook in arch/s390/pci/pci.c 
and use a defined(CONFIG_PCI) to protect the initialization inside KVM.



> 
>> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
>> new file mode 100644
>> index 000000000000..9d8799b72dbf
>> --- /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 kvm_register_hook kvm_pci_hook;
>> +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> 
> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?

OK

> 
> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

agreed no need for a separate file, it is much better.

> 
>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>> index e163aa9f6144..3b7a707e2fe5 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 (kvm_pci_hook.kvm_register)
>> +		return kvm_pci_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 (kvm_pci_hook.kvm_unregister)
>> +		return kvm_pci_hook.kvm_unregister(zdev);
> 
> No need for the return here, this is a void function calling a void function.

right.

> 
> 
> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!
> 

Thanks,
Pierre


-- 
Pierre Morel
IBM Lab Boeblingen

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

[Niklas Schnelle]

On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
> On 8/18/22 6:23 AM, Pierre Morel wrote:
> > We have a cross dependency between KVM and VFIO.
> 
> maybe add something like '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 or excluded.
> 
> s/or excluded//
> 
> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
> 
> > 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..8312ed9d1937 100644
> > --- a/arch/s390/include/asm/kvm_host.h
> > +++ b/arch/s390/include/asm/kvm_host.h

I added Janosch as second S390 KVM maintainer in case he wants to chime
in.

> > @@ -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 kvm_register_hook {
> 
> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

Hmm, I guess one could re-use the same struct for another such KVM
dependency but I lean towards the same thinking as Matt, for now this
is for zpci so stay specific we can always generalize later.

Nit: For me hook and register together sound a bit redudant, maybe
"zpci_kvm_register"? Also question for Matt as a native speaker, should
it rather be "registration" when used as a noun here?


> 
> > +	int (*kvm_register)(void *opaque, struct kvm *kvm);
> > +	void (*kvm_unregister)(void *opaque);

I do wonder if this needs to be opague "struct zpci_dev" should be
defined even if CONFIG_PCI is unset.


> > +};
> > +
> > +extern struct kvm_register_hook kvm_pci_hook;
> 
> Nit: kvm_zpci_hook ?

Analogous to zpci_kvm_regist(er|ration) I would call the variable
simply zpci_kvm i.e. the type is a registration and the variable is the
instance of it that links zpci and kvm.

> 
> >  
> >  #endif
> > diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> > index 4946fb7757d6..e173fce64c4f 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);
> > +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
> > +	kvm_pci_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 guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.
> 
> > diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> > new file mode 100644
> > index 000000000000..9d8799b72dbf
> > --- /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 kvm_register_hook kvm_pci_hook;
> > +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> 
> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
> 
> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

I'm fine with a separate file, pci.c is long enough as it is. I also
don't have a problem with having it maintained as part of S390 PCI but
logically I think it does fall more under arch/kvm/pci* so one could
argue it should be added in the MAINTAINERS file in that section.
If you change the struct name as I proposed above I would probably go
with "pci_kvm_register.c"

> 
> > diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> > index e163aa9f6144..3b7a707e2fe5 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 (kvm_pci_hook.kvm_register)
> > +		return kvm_pci_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 (kvm_pci_hook.kvm_unregister)
> > +		return kvm_pci_hook.kvm_unregister(zdev);
> 
> No need for the return here, this is a void function calling a void function.
> 
> 
> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!

Yes I agree, overall this looks good to me though I'm admittedly not
very knowledgable about how to best handle module dependencies like
this. It does look cleaner than  the symbol_get() alternative we
discussed. 

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

[Matthew Rosato]

On 8/18/22 10:20 AM, Niklas Schnelle wrote:
> On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
>> On 8/18/22 6:23 AM, Pierre Morel wrote:
>>> We have a cross dependency between KVM and VFIO.
>>
>> maybe add something like '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 or excluded.
>>
>> s/or excluded//
>>
>> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
>>
>>> 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..8312ed9d1937 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
> 
> I added Janosch as second S390 KVM maintainer in case he wants to chime
> in.
> 
>>> @@ -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 kvm_register_hook {
>>
>> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.
> 
> Hmm, I guess one could re-use the same struct for another such KVM
> dependency but I lean towards the same thinking as Matt, for now this
> is for zpci so stay specific we can always generalize later.

Yes, let's keep this zpci-specific. 

> 
> Nit: For me hook and register together sound a bit redudant, maybe
> "zpci_kvm_register"? Also question for Matt as a native speaker, should
> it rather be "registration" when used as a noun here?
> 

Maybe just drop the 'register'.  If there is a need for a 3rd function later, for example, it might not be related to registration.

e.g. struct kvm_zpci_hook {
   ...
};

extern struct kvm_zpci_hook zpci_kvm;

> 
>>
>>> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
>>> +	void (*kvm_unregister)(void *opaque);
> 
> I do wonder if this needs to be opague "struct zpci_dev" should be
> defined even if CONFIG_PCI is unset.
> 
> 
>>> +};
>>> +
>>> +extern struct kvm_register_hook kvm_pci_hook;
>>
>> Nit: kvm_zpci_hook ?
> 
> Analogous to zpci_kvm_regist(er|ration) I would call the variable
> simply zpci_kvm i.e. the type is a registration and the variable is the
> instance of it that links zpci and kvm.
> 

Yeah, see above.

>>
>>>  
>>>  #endif
>>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>>> index 4946fb7757d6..e173fce64c4f 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);
>>> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
>>> +	kvm_pci_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 guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.
>>
>>> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
>>> new file mode 100644
>>> index 000000000000..9d8799b72dbf
>>> --- /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 kvm_register_hook kvm_pci_hook;
>>> +EXPORT_SYMBOL_GPL(kvm_pci_hook);
>>
>> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
>>
>> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.
> 
> I'm fine with a separate file, pci.c is long enough as it is. I also
> don't have a problem with having it maintained as part of S390 PCI but
> logically I think it does fall more under arch/kvm/pci* so one could
> argue it should be added in the MAINTAINERS file in that section.
> If you change the struct name as I proposed above I would probably go
> with "pci_kvm_register.c"

OK, no problem with me for a separate file then, or maintaining said file.  But I guess not pci_kvm_register.c per my comments above

> 
>>
>>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>>> index e163aa9f6144..3b7a707e2fe5 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 (kvm_pci_hook.kvm_register)
>>> +		return kvm_pci_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 (kvm_pci_hook.kvm_unregister)
>>> +		return kvm_pci_hook.kvm_unregister(zdev);
>>
>> No need for the return here, this is a void function calling a void function.
>>
>>
>> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!
> 
> Yes I agree, overall this looks good to me though I'm admittedly not
> very knowledgable about how to best handle module dependencies like
> this. It does look cleaner than  the symbol_get() alternative we
> discussed. 
> 
> 

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

[Niklas Schnelle]

On Thu, 2022-08-18 at 11:13 -0400, Matthew Rosato wrote:
> On 8/18/22 10:20 AM, Niklas Schnelle wrote:
> > On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
> > > On 8/18/22 6:23 AM, Pierre Morel wrote:
> > > > We have a cross dependency between KVM and VFIO.
> > > 
> > > maybe add something like '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 or excluded.
> > > 
> > > s/or excluded//
> > > 
> > > There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
> > > 
> > > > 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..8312ed9d1937 100644
> > > > --- a/arch/s390/include/asm/kvm_host.h
> > > > +++ b/arch/s390/include/asm/kvm_host.h
> > 
> > I added Janosch as second S390 KVM maintainer in case he wants to chime
> > in.
> > 
> > > > @@ -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 kvm_register_hook {
> > > 
> > > Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.
> > 
> > Hmm, I guess one could re-use the same struct for another such KVM
> > dependency but I lean towards the same thinking as Matt, for now this
> > is for zpci so stay specific we can always generalize later.
> 
> Yes, let's keep this zpci-specific. 
> 
> > Nit: For me hook and register together sound a bit redudant, maybe
> > "zpci_kvm_register"? Also question for Matt as a native speaker, should
> > it rather be "registration" when used as a noun here?
> > 
> 
> Maybe just drop the 'register'.  If there is a need for a 3rd function later, for example, it might not be related to registration.

Yes, that sounds good and makes sense so "zpci_kvm_hook".

> 
> e.g. struct kvm_zpci_hook {
>    ...
> };
> 
> extern struct kvm_zpci_hook zpci_kvm;
> 
---8<---
> > > 
> > > > diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> > > > new file mode 100644
> > > > index 000000000000..9d8799b72dbf
> > > > --- /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 kvm_register_hook kvm_pci_hook;
> > > > +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> > > 
> > > Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
> > > 
> > > I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.
> > 
> > I'm fine with a separate file, pci.c is long enough as it is. I also
> > don't have a problem with having it maintained as part of S390 PCI but
> > logically I think it does fall more under arch/kvm/pci* so one could
> > argue it should be added in the MAINTAINERS file in that section.
> > If you change the struct name as I proposed above I would probably go
> > with "pci_kvm_register.c"
> 
> OK, no problem with me for a separate file then, or maintaining said file.  But I guess not pci_kvm_register.c per my comments above

Yes, let's go with pci_kvm_hook.c then

> 

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

[Niklas Schnelle]

---8<---
> > > > > 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<---
> > > > 
> > 
> > Ok with the two things above plus the comment by Matt incorporated:
> > 
> > Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> > 
> 
> Just a little correction, it changes nothing if the pci_kvm_hook.c goes 
> on same lines as other CONFIG_PCI depending files.
> So I put it on the same line.
> 
> Thanks
> 
> Pierre
> 

Of course yes. Thanks for fixing this and I'm assuming this would
either go through the KVM or vfio trees, correct?

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

[Pierre Morel]

On 8/19/22 12:42, Niklas Schnelle wrote:
> On Fri, 2022-08-19 at 10:44 +0200, Pierre Morel wrote:
>>
>> 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@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..")
>>>
>>> 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@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
>>>>
>>>>
>>> ---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<---
>>>
> 
> Ok with the two things above plus the comment by Matt incorporated:
> 
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> 

Just a little correction, it changes nothing if the pci_kvm_hook.c goes 
on same lines as other CONFIG_PCI depending files.
So I put it on the same line.

Thanks

Pierre

-- 
Pierre Morel
IBM Lab Boeblingen

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

[Niklas Schnelle]

On Fri, 2022-08-19 at 10:44 +0200, Pierre Morel wrote:
> 
> 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@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..")
> > 
> > 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@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
> > > 
> > > 
> > ---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<---
> > 

Ok with the two things above plus the comment by Matt incorporated:

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>

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@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..")
> 
> 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@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
>>
>>
> ---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

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

[Niklas Schnelle]

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@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..")

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.

> 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
> 
> 
---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?

> 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<---

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

[Pierre Morel]

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

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

[Matthew Rosato]

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>

> 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
> 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);
>  }

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

[Pierre Morel]

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;
 }
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
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);
 }
-- 
2.31.1