linux-kernel - Re: [PATCH v10 13/26] s390: vfio-ap: zeroize the AP queues

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Date:   Mon, 24 Sep 2018 12:42:38 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Harald Freudenberger <freude@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.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,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v10 13/26] s390: vfio-ap: zeroize the AP queues

On 09/24/2018 09:22 AM, Harald Freudenberger wrote:
> On 24.09.2018 14:16, Halil Pasic wrote:
>>
>> On 09/24/2018 01:36 PM, Cornelia Huck wrote:

(...)

>>> ...and here, we return the last error of any of the resets. Two
>>> questions:
>>>
>>> - Does it make sense to continue if we get -EIO? IOW, does "really
>>>    broken" only refer to a certain tuple and other tuples still can/need
>>>    to be reset?
>> I think it does make sense to continue, because IMHO "things are really
>> broken" is an overstatement (I mean the APQN invalid case). One could
>> argue would skipping the current card (adapter) be justified or not.
>>
>> IMHO the current code is good enough for the first shot, and we can think
>> about fine-tuning it later.
> Absolutely. The -EIO case is reached for example when the APQN
> is 'deconfigured' which means the crypto adapter is logically unplugged.
> So the -EIO case should NOT lead to some fatal actions like panic()
> or cause a KVM guest to shut down or so.
>>> - Is the return code useful in any way, as we don't know which tuple it
>>>    refers to?
>>>
>> Well, good question. It conveys that the operation can 'fail'. AFAIR -EBUSY
>> is mostly fine given what the architecture say if we are satisfied with just
>> reset. And the cases behind -EIO might actually be OK too in the same sense.
>> My guess is, that based on the return value client code can tell if we have
>> zeroize for all queues or basically just reset (like rapq). We could log that
>> to some debug facility or whatever -- I guess, but at the moment we don't care.
>>
>> In the end I think the code is good enough as is, and if we want we can
>> improve on it later.
>>
>> Regards,
>> Halil
>>

I'll note that in v7 a message was logged to indicate for which APQN the 
error occurred, but I was asked to remove the printk log messsages. I 
agree with Halil and Harald confirmed that the code is probably okay as 
it stands. I can definitely see enhancing all of AP virtualization down 
the road with some type of debug logging.

>