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

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Date:   Wed, 21 Sep 2022 14:38:51 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     farman@...ux.ibm.com, schnelle@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com, svens@...ux.ibm.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: s390: pci: register pci hooks without interpretation



On 9/20/22 21:30, Matthew Rosato 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@...ux.ibm.com>

Reviewed-by: Pierre Morel <pmorel@...ux.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);
>   }

-- 
Pierre Morel
IBM Lab Boeblingen