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

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Date:   Fri, 19 Aug 2022 10:44:10 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>, mjrosato@...ux.ibm.com
Cc:     rdunlap@...radead.org, linux-kernel@...r.kernel.org, lkp@...el.com,
        borntraeger@...ux.ibm.com, farman@...ux.ibm.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org, gor@...ux.ibm.com,
        hca@...ux.ibm.com, frankja@...ux.ibm.com
Subject: Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO



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@...radead.org>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Pierre Morel <pmorel@...ux.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@...r.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