On 3/3/21 2:47 PM, Halil Pasic wrote:
On Wed, 3 Mar 2021 12:10:11 -0500
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
On 3/3/21 10:23 AM, Halil Pasic wrote:
On Tue, 2 Mar 2021 15:43:22 -0500
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
This patch fixes a lockdep splat introduced by commit f21916ec4826
("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated").
The lockdep splat only occurs when starting a Secure Execution guest.
Crypto virtualization (vfio_ap) is not yet supported for SE guests;
however, in order to avoid this problem when support becomes available,
this fix is being provided.
[..]
@@ -1038,14 +1116,28 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
{
struct ap_matrix_mdev *m;
- list_for_each_entry(m, &matrix_dev->mdev_list, node) {
- if ((m != matrix_mdev) && (m->kvm == kvm))
- return -EPERM;
- }
+ if (kvm->arch.crypto.crycbd) {
+ matrix_mdev->kvm_busy = true;
- matrix_mdev->kvm = kvm;
- kvm_get_kvm(kvm);
- kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
+ list_for_each_entry(m, &matrix_dev->mdev_list, node) {
+ if ((m != matrix_mdev) && (m->kvm == kvm)) {
+ wake_up_all(&matrix_mdev->wait_for_kvm);
This ain't no good. kvm_busy will remain true if we take this exit. The
wake_up_all() is not needed, because we hold the lock, so nobody can
observe it if we don't forget kvm_busy set.
I suggest moving matrix_mdev->kvm_busy = true; after this loop, maybe right
before the unlock, and removing the wake_up_all().
+ return -EPERM;
+ }
+ }
+
+ kvm_get_kvm(kvm);
+ mutex_unlock(&matrix_dev->lock);
+ kvm_arch_crypto_set_masks(kvm,
+ matrix_mdev->matrix.apm,
+ matrix_mdev->matrix.aqm,
+ matrix_mdev->matrix.adm);
+ mutex_lock(&matrix_dev->lock);
+ kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
+ matrix_mdev->kvm = kvm;
+ matrix_mdev->kvm_busy = false;
+ wake_up_all(&matrix_mdev->wait_for_kvm);
+ }
return 0;
}
[..]
@@ -1300,7 +1406,21 @@ static ssize_t vfio_ap_mdev_ioctl(struct mdev_device *mdev,
ret = vfio_ap_mdev_get_device_info(arg);
break;
case VFIO_DEVICE_RESET:
- ret = vfio_ap_mdev_reset_queues(mdev);
+ matrix_mdev = mdev_get_drvdata(mdev);
+
+ /*
+ * If the KVM pointer is in the process of being set, wait until
+ * the process has completed.
+ */
+ wait_event_cmd(matrix_mdev->wait_for_kvm,
+ matrix_mdev->kvm_busy == false,
+ mutex_unlock(&matrix_dev->lock),
+ mutex_lock(&matrix_dev->lock));
+
+ if (matrix_mdev->kvm)
+ ret = vfio_ap_mdev_reset_queues(mdev);
+ else
+ ret = -ENODEV;
I don't think rejecting the reset is a good idea. I have you a more detailed
explanation of the list, where we initially discussed this question.
How do you exect userspace to react to this -ENODEV?
After reading your more detailed explanation, I have come to the
conclusion that the test for matrix_mdev->kvm should not be
performed here and the the vfio_ap_mdev_reset_queues() function
should be called regardless. Each queue assigned to the mdev
that is also bound to the vfio_ap driver will get reset and its
IRQ resources cleaned up if they haven't already been and the
other required conditions are met (i.e., see
vfio_ap_mdev_free_irq_resources()).
My point is if !->kvm the other required conditions are not met. But
yes we can go back to unconditional vfio_ap_mdev_reset_queues(mdev),
and think about the necessity of performing a
vfio_ap_mdev_reset_queues() if !->kvm later as I proposed in the other
mail.
The other conditions may or may not have been met depending
upon whether ->kvm is NULL because the VFIO_DEVICE_RESET
ioctl was invoked while the matrix_dev->lock was released
in the vfio_ap_mdev_unset_kvm() function. If that was the case,
then there is no need to clean up the IRQ resources because it
will already have been done.
On the other hand, if we don't have ->kvm because something broke,
then we may be out of luck anyway. There will certainly be no
way to unregister the GISC; however, it may still be possible
to unpin the pages if we still have q->saved_pfn.
The point is, if the queue is bound to vfio_ap, it can be reset. If we can't
clean up the IRQ resources because something is broken, then there
is nothing we can do about that.
Regards,
Halil
