Re: [PATCH v18 08/18] s390/vfio-ap: allow assignment of unavailable AP queues to mdev device

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On 3/7/22 07:31, Tony Krowiak wrote:
+         * If the input apm and aqm belong to the matrix_mdev's matrix,
+         * then move on to the next.
+         */
+        if (mdev_apm == matrix_mdev->matrix.apm &&
+            mdev_aqm == matrix_mdev->matrix.aqm)
              continue;

We may have a problem here. This check seems like it exists to stop you from
comparing an mdev's apm/aqm with itself. Obviously comparing an mdev's newly
updated apm/aqm with itself would cause a false positive sharing check, right?
If this is the case, I think the comment should be changed to reflect that.

You are correct, this check is performed to prevent comparing an mdev to
itself, I'll improve the comment.


Aside from the comment, what stops this particular series of if statements from
allowing us to configure a second mdev with the exact same apm/aqm values as an
existing mdev? If we do, then this check's continue will short circuit the rest
of the function thereby allowing that 2nd mdev even though it should be a
sharing violation.

I don't see how this is possible.

You are correct. I missed the fact that you are comparing pointers here, and not
values. Apologies. Now that I understand the code, I agree that this is fine as is.


--
-- Jason J. Herne (jjherne@xxxxxxxxxxxxx)



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