Re: [PATCH] KVM: s390: pci: register pci hooks without interpretation

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 20 Sep 2022 15:30:25 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> The kvm registration hooks must be registered even if the facilities
> necessary for zPCI interpretation are unavailable, as vfio-pci-zdev will
> expect to use the hooks regardless.
> This fixes an issue where vfio-pci-zdev will fail its open function
> because of a missing kvm_register when running on hardware that does not
> support zPCI interpretation.
> 
> Fixes: ca922fecda6c ("KVM: s390: pci: Hook to access KVM lowlevel from VFIO")
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  arch/s390/kvm/kvm-s390.c |  4 ++--
>  arch/s390/kvm/pci.c      | 14 +++++++++++---
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index e20e126944aa..5c7f5f97ea09 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -510,7 +510,7 @@ int kvm_arch_init(void *opaque)
>  		goto out;
>  	}
>  
> -	if (kvm_s390_pci_interp_allowed()) {
> +	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)) {
>  		rc = kvm_s390_pci_init();
>  		if (rc) {
>  			pr_err("Unable to allocate AIFT for PCI\n");
> @@ -532,7 +532,7 @@ int kvm_arch_init(void *opaque)
>  void kvm_arch_exit(void)
>  {
>  	kvm_s390_gib_destroy();
> -	if (kvm_s390_pci_interp_allowed())
> +	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM))
>  		kvm_s390_pci_exit();
>  	debug_unregister(kvm_s390_dbf);
>  	debug_unregister(kvm_s390_dbf_uv);
> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> index 90aaba80696a..c50c1645c0ae 100644
> --- a/arch/s390/kvm/pci.c
> +++ b/arch/s390/kvm/pci.c
> @@ -672,23 +672,31 @@ int kvm_s390_pci_zpci_op(struct kvm *kvm, struct kvm_s390_zpci_op *args)
>  
>  int kvm_s390_pci_init(void)
>  {
> +	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
> +	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
> +
> +	if (!kvm_s390_pci_interp_allowed())
> +		return 0;
> +
>  	aift = kzalloc(sizeof(struct zpci_aift), GFP_KERNEL);
>  	if (!aift)
>  		return -ENOMEM;
>  
>  	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;
>  }
>  
>  void kvm_s390_pci_exit(void)
>  {
> -	mutex_destroy(&aift->aift_lock);
>  	zpci_kvm_hook.kvm_register = NULL;
>  	zpci_kvm_hook.kvm_unregister = NULL;
>  
> +	if (!kvm_s390_pci_interp_allowed())
> +		return;
> +
> +	mutex_destroy(&aift->aift_lock);
> +
>  	kfree(aift);
>  }