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

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Date:   Mon, 15 Aug 2022 11:43:15 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     kernel test robot <lkp@...el.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] vfio-pci/zdev: require KVM to be built-in

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@...radead.org>
> Reported-by: kernel test robot <lkp@...el.com>
> Cc: Matthew Rosato <mjrosato@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
> Cc: Pierre Morel <pmorel@...ux.ibm.com>
> Cc: Eric Farman <farman@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> Cc: kvm@...r.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