linux-kernel - Re: [PATCH] s390/vfio-ap: fix sysfs status attribute for AP queue devices

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Message-ID: <12aef605a2add44afca75cc647674cdb@linux.ibm.com>
Date:   Tue, 07 Nov 2023 09:07:45 +0100
From:   Harald Freudenberger <freude@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, stable@...r.kernel.org
Subject: Re: [PATCH] s390/vfio-ap: fix sysfs status attribute for AP queue
 devices

On 2023-11-06 17:03, Tony Krowiak wrote:
> PING
> This patch is pretty straight forward, does anyone see a reason why
> this shouldn't be integrated?
> 
> On 10/20/23 16:48, Tony Krowiak wrote:
>> The 'status' attribute for AP queue devices bound to the vfio_ap 
>> device
>> driver displays incorrect status when the mediated device is attached 
>> to a
>> guest, but the queue device is not passed through. In the current
>> implementation, the status displayed is 'in_use' which is not correct; 
>> it
>> should be 'assigned'. This can happen if one of the queue devices
>> associated with a given adapter is not bound to the vfio_ap device 
>> driver.
>> For example:
>> 
>> Queues listed in /sys/bus/ap/drivers/vfio_ap:
>> 14.0005
>> 14.0006
>> 14.000d
>> 16.0006
>> 16.000d
>> 
>> Queues listed in /sys/devices/vfio_ap/matrix/$UUID/matrix
>> 14.0005
>> 14.0006
>> 14.000d
>> 16.0005
>> 16.0006
>> 16.000d
>> 
>> Queues listed in /sys/devices/vfio_ap/matrix/$UUID/guest_matrix
>> 14.0005
>> 14.0006
>> 14.000d
>> 
>> The reason no queues for adapter 0x16 are listed in the guest_matrix 
>> is
>> because queue 16.0005 is not bound to the vfio_ap device driver, so no
>> queue associated with the adapter is passed through to the guest;
>> therefore, each queue device for adapter 0x16 should display 
>> 'assigned'
>> instead of 'in_use', because those queues are not in use by a guest, 
>> but
>> only assigned to the mediated device.
>> 
>> Let's check the AP configuration for the guest to determine whether a
>> queue device is passed through before displaying a status of 'in_use'.
>> 
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> Fixes: f139862b92cf ("s390/vfio-ap: add status attribute to AP queue 
>> device's sysfs dir")
>> Cc: stable@...r.kernel.org
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
>> b/drivers/s390/crypto/vfio_ap_ops.c
>> index 4db538a55192..871c14a6921f 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -1976,6 +1976,7 @@ static ssize_t status_show(struct device *dev,
>>   {
>>   	ssize_t nchars = 0;
>>   	struct vfio_ap_queue *q;
>> +	unsigned long apid, apqi;
>>   	struct ap_matrix_mdev *matrix_mdev;
>>   	struct ap_device *apdev = to_ap_dev(dev);
>>   @@ -1984,7 +1985,11 @@ static ssize_t status_show(struct device 
>> *dev,
>>   	matrix_mdev = vfio_ap_mdev_for_queue(q);
>>     	if (matrix_mdev) {
>> -		if (matrix_mdev->kvm)
>> +		apid = AP_QID_CARD(q->apqn);
>> +		apqi = AP_QID_QUEUE(q->apqn);
>> +		if (matrix_mdev->kvm &&
>> +		    test_bit_inv(apid, matrix_mdev->shadow_apcb.apm) &&
>> +		    test_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm))
>>   			nchars = scnprintf(buf, PAGE_SIZE, "%s\n",
>>   					   AP_QUEUE_IN_USE);
>>   		else

I can give you an
Acked-by: Harald Freudenberger <freude@...ux.ibm.com>
for this. Your explanation sounds sane to me and fixes a wrong
display. However, I am not familiar with the code so, I can't tell
if that's correct.
Just a remark: How can it happen that one queue is not bound to the vfio 
dd?
Didn't we actively remove the unbind possibility from the sysfs for 
devices
assigned to the vfio dd?