linux-kernel - Re: [PATCH v5 04/13] s390: vfio-ap: base implementation of VFIO AP device driver

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Message-Id: <ea3904e7-0c7e-c8d4-556f-fc18edfe6709@linux.vnet.ibm.com>
Date:   Wed, 16 May 2018 07:45:00 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     pmorel@...ux.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 04/13] s390: vfio-ap: base implementation of VFIO AP
 device driver

On 05/16/2018 04:21 AM, Pierre Morel wrote:
> On 07/05/2018 17:11, Tony Krowiak wrote:
>> Introduces a new AP device driver. This device driver
>> is built on the VFIO mediated device framework. The framework
>> provides sysfs interfaces that facilitate passthrough
>> access by guests to devices installed on the linux host.
> ...snip...
>> +static int vfio_ap_queue_dev_probe(struct ap_device *apdev)
>> +{
>
> You should take care of the ap devices when they are added or removed
> from the matrix.
> I suggest you add a remove callback to avoid unbinding a queue while
> it is assigned to a guest.

This is not possible without a change to the AP bus. The remove callback
returns void, so there is no way to indicate to the AP bus not to remove
the queue device. I'll talk to Harald about this.


>
>
>> +    return 0;
>> +}
>> +
>> +static void vfio_ap_matrix_dev_release(struct device *dev)
>> +{
>> +    struct ap_matrix *ap_matrix = dev_get_drvdata(dev);
>> +
>> +    kfree(ap_matrix);
>> +}
> ...snip...
>