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

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Date:   Thu, 19 Sep 2019 12:34:34 +0200
From:   Halil Pasic <pasic@...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, 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 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.

Regards,
Halil