From: Halil Pasic <pasic@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, stable@vger.kernel.org,
borntraeger@de.ibm.com, kwankhede@nvidia.com,
pbonzini@redhat.com, alex.williamson@redhat.com,
pasic@linux.vnet.ibm.com
Subject: Re: [PATCH 1/1] s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks
Date: Wed, 10 Feb 2021 16:32:37 +0100 [thread overview]
Message-ID: <20210210163237.315d9a68.pasic@linux.ibm.com> (raw)
In-Reply-To: <20210210162429.261fc17c.pasic@linux.ibm.com>
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.
next prev parent reply other threads:[~2021-02-10 15:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-09 19:48 [PATCH 0/1] fix circular lockdep when staring SE guest Tony Krowiak
2021-02-09 19:48 ` [PATCH 1/1] s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks Tony Krowiak
2021-02-10 10:53 ` Cornelia Huck
2021-02-10 15:24 ` Halil Pasic
2021-02-10 15:32 ` Halil Pasic [this message]
2021-02-10 22:05 ` Tony Krowiak
2021-02-10 22:46 ` Halil Pasic
2021-02-11 14:21 ` Tony Krowiak
2021-02-11 16:47 ` Halil Pasic
2021-02-11 19:18 ` Tony Krowiak
2021-02-10 22:03 ` Tony Krowiak
2021-02-10 20:34 ` Tony Krowiak
2021-02-11 12:23 ` Cornelia Huck
2021-02-11 14:38 ` Tony Krowiak
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