Re: [PATCH v4 2/2] s390/vfio-ap: control access to PQAP(AQIC) interception handler

Jason Gunthorpe
2021-05-25T15:11:21Z

On Tue, May 25, 2021 at 11:08:22AM -0400, Tony Krowiak wrote:

> > Why can't you put the locks in the right order? It looked trivial, I'm confused.
>
> Because the handle_pqap() function in priv.c does not have access to the
> matrix_dev lock.

Based on the sketch made the handle_pqap() should only handle the
arch.crypto.rwsem.

When it calls the hook it gets the matrix dev

This sets the lock order as always: rwsem then matrix_dev

Of the other two places:

@@ -352,8 +352,7 @@ static int vfio_ap_mdev_create(struct mdev_device *mdev)
+ down_write(&&vcpu->kvm->arch.crypto.rwsem);
mutex_lock(&matrix_dev->lock);

Obviously correct

@@ -1202,7 +1203,9 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
mutex_lock(&matrix_dev->lock);
vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
+ down_write(&matrix_mdev->kvm->arch.crypto.rwsem);
matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
+ up_write(&matrix_mdev->kvm->arch.crypto.rwsem);

This is inverted

Just move the down_write up two lines

What is missing?

Jason