linux-kernel - Re: [PATCH v6 04/10] s390: vfio-ap: filter CRYCB bits for unavailable queue devices

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Date:   Fri, 20 Sep 2019 10:24:19 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, mjrosato@...ux.ibm.com, pmorel@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        jjherne@...ux.ibm.com
Subject: Re: [PATCH v6 04/10] s390: vfio-ap: filter CRYCB bits for unavailable
 queue devices

On 9/19/19 6:34 AM, Halil Pasic wrote:
> On Fri, 13 Sep 2019 17:26:52 -0400
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> 
>> +static void vfio_ap_mdev_get_crycb_matrix(struct ap_matrix_mdev *matrix_mdev)
>> +{
>> +	unsigned long apid, apqi;
>> +	unsigned long masksz = BITS_TO_LONGS(AP_DEVICES) *
>> +			       sizeof(unsigned long);
>> +
>> +	memset(matrix_mdev->crycb.apm, 0, masksz);
>> +	memset(matrix_mdev->crycb.apm, 0, masksz);
>> +	memcpy(matrix_mdev->crycb.adm, matrix_mdev->matrix.adm, masksz);
>> +
>> +	for_each_set_bit_inv(apid, matrix_mdev->matrix.apm,
>> +			     matrix_mdev->matrix.apm_max + 1) {
>> +		for_each_set_bit_inv(apqi, matrix_mdev->matrix.aqm,
>> +				     matrix_mdev->matrix.aqm_max + 1) {
>> +			if (vfio_ap_find_queue(AP_MKQID(apid, apqi))) {
>> +				if (!test_bit_inv(apid, matrix_mdev->crycb.apm))
>> +					set_bit_inv(apid,
>> +						    matrix_mdev->crycb.apm);
>> +				if (!test_bit_inv(apqi, matrix_mdev->crycb.aqm))
>> +					set_bit_inv(apqi,
>> +						    matrix_mdev->crycb.aqm);
>> +			}
>> +		}
>> +	}
>> +}
> 
> Even with the discussed typo fixed (zero crycb.aqm) this procedure does
> not make sense to me. :(
> 
> If in doubt please consider the following example:
> matrix_mdev->matrix.apm and matrix_mdev->matrix.aqm have both just bits
> 0 and 1 set (i.e. first byte 0xC0 the rest of the bytes 0x0). Queues
> bound to the vfio_ap driver (0,0), (0,1), (1,0); not bound to vfio_ap is
> however (1,1). If I read this correctly this filtering logic would grant
> access to (1,1) which seems to contradict with the stated intention.

Yep, I see your point. I'll have to rework this code.

> 
> Regards,
> Halil
> 
> 
>