linux-kernel - Re: [PATCH] s390/vfio-ap: handle response code 01 on queue reset

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Date:   Mon, 4 Dec 2023 12:05:19 -0500
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        frankja@...ux.ibm.com, imbrenda@...ux.ibm.com, david@...hat.com,
        Reinhard Buendgen <BUENDGEN@...ibm.com>
Subject: Re: [PATCH] s390/vfio-ap: handle response code 01 on queue reset



On 12/4/23 11:15, Halil Pasic wrote:
> On Mon, 4 Dec 2023 16:16:31 +0100
> Christian Borntraeger <borntraeger@...ux.ibm.com> wrote:
> 
>> Am 04.12.23 um 15:53 schrieb Tony Krowiak:
>>>
>>>
>>> On 11/29/23 12:12, Christian Borntraeger wrote:
>>>> Am 29.11.23 um 15:35 schrieb Tony Krowiak:
>>>>> In the current implementation, response code 01 (AP queue number not valid)
>>>>> is handled as a default case along with other response codes returned from
>>>>> a queue reset operation that are not handled specifically. Barring a bug,
>>>>> response code 01 will occur only when a queue has been externally removed
>>>>> from the host's AP configuration; nn this case, the queue must
>>>>> be reset by the machine in order to avoid leaking crypto data if/when the
>>>>> queue is returned to the host's configuration. The response code 01 case
>>>>> will be handled specifically by logging a WARN message followed by cleaning
>>>>> up the IRQ resources.
>>>>>   
>>>>
>>>> To me it looks like this can be triggered by the LPAR admin, correct? So it
>>>> is not desireable but possible.
>>>> In that case I prefer to not use WARN, maybe use dev_warn or dev_err instead.
>>>> WARN can be a disruptive event if panic_on_warn is set.
>>>
>>> Yes, it can be triggered by the LPAR admin. I can't use dev_warn here because we don't have a reference to any device, but I can use pr_warn if that suffices.
>>
>> Ok, please use pr_warn then.
> 
> Shouldn't we rather make this an 'info'. I mean we probably do not want
> people complaining about this condition. Yes it should be a best practice
> to coordinate such things with the guest, and ideally remove the resource
> from the guest first. But AFAIU our stack is supposed to be able to
> handle something like this. IMHO issuing a warning is excessive measure.
> I know Reinhard and Tony probably disagree with the last sentence
> though.

I don't feel strongly one way or the other. Anybody else?

> 
> Regards,
> Halil