Re: [PATCH v7 09/22] s390: vfio-ap: register matrix device with VFIO mdev framework

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On 07/27/2018 01:17 PM, Cornelia Huck wrote:
On Fri, 27 Jul 2018 13:13:40 +0200
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:

@@ -65,6 +66,21 @@ static int vfio_ap_matrix_dev_create(void)
   {
   	int ret;
+ mutex_init(&matrix_dev.lock);
+	INIT_LIST_HEAD(&matrix_dev.mdev_list);
+
+	/* Test if PQAP(QCI) instruction is available */
+	if (test_facility(12)) {
+		ret = ap_qci(&matrix_dev.info);
+		if (ret && (ret != -EOPNOTSUPP)) {

So, is facility 12 a pre-req for PQAP(QCI)? Can the code work if
matrix_dev.info is not populated?

Yes and yes. It's basically only used in vfio_ap_matrix_init() and it
has fallbacks.

Ok. So facility 12 is required but not sufficient for PQAP(QCI) to be
available? (Just asking as I cannot check the doc; if it works with
fallbacks I'm fine.)


AFAIR it should be sufficient in our case. My guess is that the non 0
return code stands for program exceptions that are not related to the
availability of QCI.




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