linux-kernel - Re: [PATCH v10 07/16] s390/vfio-ap: sysfs attribute to display the guest's matrix

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Date:   Sat, 26 Sep 2020 09:16:09 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        freude@...ux.ibm.com, borntraeger@...ibm.com,
        mjrosato@...ux.ibm.com, alex.williamson@...hat.com,
        kwankhede@...dia.com, fiuczy@...ux.ibm.com, frankja@...ux.ibm.com,
        david@...hat.com, imbrenda@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com
Subject: Re: [PATCH v10 07/16] s390/vfio-ap: sysfs attribute to display the
 guest's matrix

On Fri, 18 Sep 2020 13:09:25 -0400
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> 
> 
> On 9/17/20 10:34 AM, Cornelia Huck wrote:
> > On Fri, 21 Aug 2020 15:56:07 -0400
> > Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> >
> >> The matrix of adapters and domains configured in a guest's CRYCB may
> >> differ from the matrix of adapters and domains assigned to the matrix mdev,
> >> so this patch introduces a sysfs attribute to display the matrix of a guest
> >> using the matrix mdev. For a matrix mdev denoted by $uuid, the crycb for a
> >> guest using the matrix mdev can be displayed as follows:
> >>
> >>     cat /sys/devices/vfio_ap/matrix/$uuid/guest_matrix
> >>
> >> If a guest is not using the matrix mdev at the time the crycb is displayed,
> >> an error (ENODEV) will be returned.
> >>
> >> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> >> ---
> >>   drivers/s390/crypto/vfio_ap_ops.c | 58 +++++++++++++++++++++++++++++++
> >>   1 file changed, 58 insertions(+)
> >>
> >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> >> index efb229033f9e..30bf23734af6 100644
> >> --- a/drivers/s390/crypto/vfio_ap_ops.c
> >> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> >> @@ -1119,6 +1119,63 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
> >>   }
> >>   static DEVICE_ATTR_RO(matrix);
> >>   
> >> +static ssize_t guest_matrix_show(struct device *dev,
> >> +				 struct device_attribute *attr, char *buf)
> >> +{
> >> +	struct mdev_device *mdev = mdev_from_dev(dev);
> >> +	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
> >> +	char *bufpos = buf;
> >> +	unsigned long apid;
> >> +	unsigned long apqi;
> >> +	unsigned long apid1;
> >> +	unsigned long apqi1;
> >> +	unsigned long napm_bits = matrix_mdev->shadow_apcb.apm_max + 1;
> >> +	unsigned long naqm_bits = matrix_mdev->shadow_apcb.aqm_max + 1;
> >> +	int nchars = 0;
> >> +	int n;
> >> +
> >> +	if (!vfio_ap_mdev_has_crycb(matrix_mdev))
> >> +		return -ENODEV;
> >> +
> >> +	apid1 = find_first_bit_inv(matrix_mdev->shadow_apcb.apm, napm_bits);
> >> +	apqi1 = find_first_bit_inv(matrix_mdev->shadow_apcb.aqm, naqm_bits);
> >> +
> >> +	mutex_lock(&matrix_dev->lock);
> >> +
> >> +	if ((apid1 < napm_bits) && (apqi1 < naqm_bits)) {
> >> +		for_each_set_bit_inv(apid, matrix_mdev->shadow_apcb.apm,
> >> +				     napm_bits) {
> >> +			for_each_set_bit_inv(apqi,
> >> +					     matrix_mdev->shadow_apcb.aqm,
> >> +					     naqm_bits) {
> >> +				n = sprintf(bufpos, "%02lx.%04lx\n", apid,
> >> +					    apqi);
> >> +				bufpos += n;
> >> +				nchars += n;
> >> +			}
> >> +		}
> >> +	} else if (apid1 < napm_bits) {
> >> +		for_each_set_bit_inv(apid, matrix_mdev->shadow_apcb.apm,
> >> +				     napm_bits) {
> >> +			n = sprintf(bufpos, "%02lx.\n", apid);
> >> +			bufpos += n;
> >> +			nchars += n;
> >> +		}
> >> +	} else if (apqi1 < naqm_bits) {
> >> +		for_each_set_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm,
> >> +				     naqm_bits) {
> >> +			n = sprintf(bufpos, ".%04lx\n", apqi);
> >> +			bufpos += n;
> >> +			nchars += n;
> >> +		}
> >> +	}
> >> +
> >> +	mutex_unlock(&matrix_dev->lock);
> >> +
> >> +	return nchars;
> >> +}
> > This basically looks like a version of matrix_show() operating on the
> > shadow apcb. I'm wondering if we could consolidate these two functions
> > by passing in the structure to operate on as a parameter? Might not be
> > worth the effort, though.
> 
> We still need the two functions because they back the mdev's
> sysfs matrix and guest_matrix attributes, but we could call a function.
> I'm not sure it buys us much though.

The logic seems identical with the exception that the guest variant
checks if vfio_ap_mdev_has_crycb(matrix_mdev). I'm not a big fan of
duplicated code, and especially not in such close proximity. I'm voting
for factoring out the common logic.

Otherwise looks OK.

Regards,
Halil