Messages in this thread | | | Subject | Re: [PATCHv2 08/10] vfio/mdev: Improve the create/remove sequence | From | Pierre Morel <> | Date | Thu, 9 May 2019 18:26:59 +0200 |
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On 09/05/2019 11:06, Cornelia Huck wrote: > [vfio-ap folks: find a question regarding removal further down] > > On Wed, 8 May 2019 22:06:48 +0000 > Parav Pandit <parav@mellanox.com> wrote: > >>> -----Original Message----- >>> From: Cornelia Huck <cohuck@redhat.com> >>> Sent: Wednesday, May 8, 2019 12:10 PM >>> To: Parav Pandit <parav@mellanox.com> >>> Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org; >>> kwankhede@nvidia.com; alex.williamson@redhat.com; cjia@nvidia.com >>> Subject: Re: [PATCHv2 08/10] vfio/mdev: Improve the create/remove >>> sequence >>> >>> On Tue, 30 Apr 2019 17:49:35 -0500 >>> Parav Pandit <parav@mellanox.com> wrote: >>>
...snip...
>>>> @@ -373,16 +330,15 @@ int mdev_device_remove(struct device *dev, >>> bool force_remove) >>>> mutex_unlock(&mdev_list_lock); >>>> >>>> type = to_mdev_type(mdev->type_kobj); >>>> + mdev_remove_sysfs_files(dev, type); >>>> + device_del(&mdev->dev); >>>> parent = mdev->parent; >>>> + ret = parent->ops->remove(mdev); >>>> + if (ret) >>>> + dev_err(&mdev->dev, "Remove failed: err=%d\n", ret); >>> >>> I think carrying on with removal regardless of the return code of the >>> ->remove callback makes sense, as it simply matches usual practice. >>> However, are we sure that every vendor driver works well with that? I think >>> it should, as removal from bus unregistration (vs. from the sysfs >>> file) was always something it could not veto, but have you looked at the >>> individual drivers? >>> >> I looked at following drivers a little while back. >> Looked again now. >> >> drivers/gpu/drm/i915/gvt/kvmgt.c which clears the handle valid in intel_vgpu_release(), which should finish first before remove() is invoked. >> >> s390 vfio_ccw_mdev_remove() driver drivers/s390/cio/vfio_ccw_ops.c remove() always returns 0. >> s39 crypo fails the remove() once vfio_ap_mdev_release marks kvm null, which should finish before remove() is invoked. > > That one is giving me a bit of a headache (the ->kvm reference is > supposed to keep us from detaching while a vm is running), so let's cc: > the vfio-ap maintainers to see whether they have any concerns. >
We are aware of this race and we did correct this in the IRQ patches for which it would have become a real issue. We now increment/decrement the KVM reference counter inside open and release. Should be right after this.
Thanks for the cc, Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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