Messages in this thread | | | Subject | Re: [PATCH v5 4/7] s390: ap: setup relation betwen KVM and mediated device | From | Pierre Morel <> | Date | Tue, 19 Mar 2019 15:23:13 +0100 |
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On 19/03/2019 12:54, Halil Pasic wrote: > On Tue, 19 Mar 2019 10:38:42 +0100 > Pierre Morel <pmorel@linux.ibm.com> wrote: > >> On 15/03/2019 19:15, Halil Pasic wrote: >>> On Wed, 13 Mar 2019 17:05:01 +0100 >>> Pierre Morel <pmorel@linux.ibm.com> wrote: >>> >>>> When the mediated device is open we setup the relation with KVM unset it >>>> when the mediated device is released. >>>> >>>> We ensure KVM is present on opening of the mediated device. >>>> >>>> We ensure that KVM survives the mediated device, and establish a direct >>> >>> survives? >> >> what alternative do you prefer? >> > > Increase kvm's refcount to ensure the guest is alive when the > ap_matrix_mdev is active. An ap mp_matrix becomes active with > a successful open() and ceases to be active with a release().
Right, it is mdev usage not mdev.
> > Your sentence was materially wrong as the mdev is allowed to outlive > the KVM. BTW survive tends to have an 'in spite of' note to it, which > outlive does not. vfio-ap is, I hope, not a calamity that threatens > the life of KVM ;). https://en.oxforddictionaries.com/definition/survive
Thanks, your description is much better.
> >>> >>>> link from KVM to the mediated device to simplify the relationship. >>>> >>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>>> --- >> >> ...snip... >> >>>> static int vfio_ap_mdev_group_notifier(struct notifier_block *nb, >>>> unsigned long action, void *data) >>>> { >>>> - int ret; >>>> struct ap_matrix_mdev *matrix_mdev; >>>> >>>> if (action != VFIO_GROUP_NOTIFY_SET_KVM) >>>> return NOTIFY_OK; >>>> >>>> matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier); >>>> - >>>> - if (!data) { >>>> - matrix_mdev->kvm = NULL; >>>> - return NOTIFY_OK; >>>> - } >>>> - >>>> - ret = vfio_ap_mdev_set_kvm(matrix_mdev, data); >>>> - if (ret) >>>> - return NOTIFY_DONE; >>>> - >>>> - /* If there is no CRYCB pointer, then we can't copy the masks */ >>>> - if (!matrix_mdev->kvm->arch.crypto.crycbd) >>>> - return NOTIFY_DONE; >>>> - >>>> - kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm, >>>> - matrix_mdev->matrix.aqm, >>>> - matrix_mdev->matrix.adm); >>>> + matrix_mdev->kvm = data; >>>> >>>> return NOTIFY_OK; >>>> } >>>> @@ -888,6 +873,12 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> if (ret) >>>> goto err_group; >>>> >>>> + /* We do not support opening the mediated device without KVM */ >>>> + if (!matrix_mdev->kvm) { >>>> + ret = -ENODEV; >>>> + goto err_group; >>>> + } >>>> + >>>> matrix_mdev->iommu_notifier.notifier_call = vfio_ap_mdev_iommu_notifier; >>>> events = VFIO_IOMMU_NOTIFY_DMA_UNMAP; >>>> >>>> @@ -896,8 +887,15 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> if (ret) >>>> goto err_iommu; >>>> >>>> + ret = vfio_ap_mdev_set_kvm(matrix_mdev); >>> >>> At this point the matrix_mdev->kvm ain't guaranteed to be valid IMHO. Or >>> am I wrong? If I'm right kvm_get_kvm(matrix_mdev->kvm) could be too late. >> >> What about the if (!matrix_mdev->kvm) 10 lines above ? >> > > That check is not sufficient. > > You should do the kvm_get_kvm() in vfio_ap_mdev_group_notifier(). VFIO > must ensure that the kvm pointer you get is valid, in a sense that it > points to a valid struct kvm and the kvm object is alive, while you are > in the callback. But not beyond. > > If another thread were to decrement the refcount of the kvm object you > would end up with matrix_mdev->kvm pointing to an object that has already > died. > > Does my analysis make sense to you?
Yes thanks the explication is good, it would have been worth to get it the first time.
> >>> >>>> + if (ret) >>>> + goto err_kvm; >>>> + >>>> return 0; >>>> >>>> +err_kvm: >>>> + vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY, >>>> + &matrix_mdev->iommu_notifier); >>>> err_iommu: >>>> vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY, >>>> &matrix_mdev->group_notifier); >>>> @@ -906,19 +904,33 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev) >>>> return ret; >>>> } >>>> >>>> -static void vfio_ap_mdev_release(struct mdev_device *mdev) >>>> +static int vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) >>>> { >>>> - struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); >>>> + struct kvm *kvm = matrix_mdev->kvm; >>>> >>>> if (matrix_mdev->kvm) >>>> kvm_arch_crypto_clear_masks(matrix_mdev->kvm); >>> >>> This still conditional? >> >> Yes, nothing to clear if there is no KVM. >> > > Since we have ensured the open only works if there is a KVM at that > point in time, and we have taken a reference to KVM, I would expect > KVM can not go away before we give up our reference.
Right.
Thanks, Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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