linux-kernel - Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback

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Message-Id: <93cd0f46-a410-51c8-00b9-810c1b3d3ae2@linux.ibm.com>
Date:   Thu, 24 May 2018 11:08:23 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v5 11/13] KVM: s390: implement mediated device open
 callback

On 23/05/2018 16:45, Tony Krowiak wrote:
> On 05/16/2018 04:03 AM, Pierre Morel wrote:
>> On 07/05/2018 17:11, Tony Krowiak wrote:
>>> Implements the open callback on the mediated matrix device.
>>> The function registers a group notifier to receive notification
>>> of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
>>> the vfio_ap device driver will get access to the guest's
>>> kvm structure. With access to this structure the driver will:
>>>
>>> 1. Ensure that only one mediated device is opened for the guest

You should explain why.

>>>
>>> 2. Configure access to the AP devices for the guest.
>>>
...snip...
>>> +void kvm_ap_refcount_inc(struct kvm *kvm)
>>> +{
>>> +    atomic_inc(&kvm->arch.crypto.aprefs);
>>> +}
>>> +EXPORT_SYMBOL(kvm_ap_refcount_inc);
>>> +
>>> +void kvm_ap_refcount_dec(struct kvm *kvm)
>>> +{
>>> +    atomic_dec(&kvm->arch.crypto.aprefs);
>>> +}
>>> +EXPORT_SYMBOL(kvm_ap_refcount_dec);
>>
>> Why are these functions inside kvm-ap ?
>> Will anyone use this outer of vfio-ap ?
>
> As I've stated before, I made the choice to contain all interfaces that
> access KVM in kvm-ap because I don't think it is appropriate for the 
> device
> driver to have to have "knowledge" of the inner workings of KVM. Why does
> it matter whether any entity outside of the vfio_ap device driver calls
> these functions? I could ask a similar question if the interfaces were
> contained in vfio-ap; what if another device driver needs access to these
> interfaces?

This is very driver specific and only used during initialization.
It is not a common property of the cryptographic interface.

I really think you should handle this inside the driver.

Pierre


...snip...


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany