Messages in this thread | | | Subject | Re: [PATCH 1/1] s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks | From | Tony Krowiak <> | Date | Wed, 10 Feb 2021 17:05:48 -0500 |
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On 2/10/21 10:32 AM, Halil Pasic wrote: > On Wed, 10 Feb 2021 16:24:29 +0100 > Halil Pasic <pasic@linux.ibm.com> wrote: > >>> Maybe you could >>> - grab a reference to kvm while holding the lock >>> - call the mask handling functions with that kvm reference >>> - lock again, drop the reference, and do the rest of the processing? >> I agree, matrix_mdev->kvm can go NULL any time and we are risking >> a null pointer dereference here. >> >> Another idea would be to do >> >> >> static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >> { >> struct kvm *kvm; >> >> mutex_lock(&matrix_dev->lock); >> if (matrix_mdev->kvm) { >> kvm = matrix_mdev->kvm; >> matrix_mdev->kvm = NULL; >> mutex_unlock(&matrix_dev->lock); >> kvm_arch_crypto_clear_masks(kvm); >> mutex_lock(&matrix_dev->lock); >> matrix_mdev->kvm->arch.crypto.pqap_hook = NULL; > s/matrix_mdev->kvm/kvm >> vfio_ap_mdev_reset_queues(matrix_mdev->mdev); >> kvm_put_kvm(kvm); >> } >> mutex_unlock(&matrix_dev->lock); >> } >> >> That way only one unset would actually do the unset and cleanup >> and every other invocation would bail out with only checking >> matrix_mdev->kvm. > But the problem with that is that we enable the the assign/unassign > prematurely, which could interfere wit reset_queues(). Forget about > it.
Not sure what you mean by this.
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