From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [v3 4/5] vfio: implement APIs to set/put kvm to/from vfio group Date: Thu, 10 Nov 2016 08:37:58 -0700 Message-ID: <20161110083758.3f9a694f@t450s.home> References: <1477895706-22824-1-git-send-email-jike.song@intel.com> <1477895706-22824-5-git-send-email-jike.song@intel.com> <20161107110412.5db26fd4@t450s.home> <20161107112834.2aa971df@t450s.home> <9e83a26f-e5dc-ed91-a1b5-c6f165eed7ed@redhat.com> <58231B5C.3010506@intel.com> <20161109105352.3337acbb@t450s.home> <5823F32A.7040807@intel.com> <58240DE3.70902@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , guangrong.xiao@linux.intel.com, kwankhede@nvidia.com, cjia@nvidia.com, kevin.tian@intel.com, kvm@vger.kernel.org To: Jike Song Return-path: Received: from mx1.redhat.com ([209.132.183.28]:52380 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933658AbcKJPiE (ORCPT ); Thu, 10 Nov 2016 10:38:04 -0500 In-Reply-To: <58240DE3.70902@intel.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, 10 Nov 2016 14:04:19 +0800 Jike Song wrote: > On 11/10/2016 12:10 PM, Jike Song wrote: > > On 11/10/2016 01:53 AM, Alex Williamson wrote: > >> On Wed, 09 Nov 2016 20:49:32 +0800 > >> Jike Song wrote: > >> > >>> On 11/08/2016 04:45 AM, Paolo Bonzini wrote: > >>>> On 07/11/2016 19:28, Alex Williamson wrote: > >>>>>>> Can the reference become invalid? > >>>>>> > >>>>>> No, this is guaranteed by virt/kvm/vfio.c + the udata.lock mutex (which > >>>>>> probably should be renamed...). > >>>>> > >>>>> The caller gets a reference to kvm, but there's no guarantee that the > >>>>> association of that kvm reference to the group stays valid. Once we're > >>>>> outside of that mutex, we might as well consider that kvm:group > >>>>> association stale. > >>>>> > >>>>>>> The caller may still hold > >>>>>>> a kvm references, but couldn't the group be detached from one kvm > >>>>>>> instance and re-attached to another? > >>>>>> > >>>>>> Can this be handled by the vendor driver? Does it get a callback when > >>>>>> it's detached from a KVM instance? > >>>>> > >>>>> The only release callback through vfio is when the user closes the > >>>>> device, the code in this series is the full extent of vfio awareness of > >>>>> kvm. Thanks, > >>>> > >>>> Maybe there should be an mdev callback at the point of association and > >>>> deassociation between VFIO and KVM. Then the vendor driver can just use > >>>> the same mutex for association, deassociation and usage. I'm not even > >>>> sure that these patches are necessary once you have that callback. > >>> > >>> Hi Alex & Paolo, > >>> > >>> So I cooked another draft version of this, there is no kvm pointer saved > >>> in vfio_group in this version, and notifier will be called on attach/detach, > >>> please kindly have a look :-) > >>> > >>> > >>> -- > >>> Thanks, > >>> Jike > >>> > >>> > >>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > >>> index ed2361e4..20b5da9 100644 > >>> --- a/drivers/vfio/vfio.c > >>> +++ b/drivers/vfio/vfio.c > >>> @@ -34,6 +34,7 @@ > >>> #include > >>> #include > >>> #include > >>> +#include > >>> > >>> #define DRIVER_VERSION "0.3" > >>> #define DRIVER_AUTHOR "Alex Williamson " > >>> @@ -86,6 +87,10 @@ struct vfio_group { > >>> struct mutex unbound_lock; > >>> atomic_t opened; > >>> bool noiommu; > >>> + struct { > >>> + struct mutex lock; > >>> + struct blocking_notifier_head notifier; > >>> + } udata; > >>> }; > >>> > >>> struct vfio_device { > >>> @@ -333,6 +338,7 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group) > >>> mutex_init(&group->device_lock); > >>> INIT_LIST_HEAD(&group->unbound_list); > >>> mutex_init(&group->unbound_lock); > >>> + mutex_init(&group->udata.lock); > >>> atomic_set(&group->container_users, 0); > >>> atomic_set(&group->opened, 0); > >>> group->iommu_group = iommu_group; > >>> @@ -414,10 +420,11 @@ static void vfio_group_release(struct kref *kref) > >>> iommu_group_put(iommu_group); > >>> } > >>> > >>> -static void vfio_group_put(struct vfio_group *group) > >>> +void vfio_group_put(struct vfio_group *group) > >>> { > >>> kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock); > >>> } > >>> +EXPORT_SYMBOL_GPL(vfio_group_put); > >>> > >>> /* Assume group_lock or group reference is held */ > >>> static void vfio_group_get(struct vfio_group *group) > >>> @@ -480,7 +487,7 @@ static struct vfio_group *vfio_group_get_from_minor(int minor) > >>> return group; > >>> } > >>> > >>> -static struct vfio_group *vfio_group_get_from_dev(struct device *dev) > >>> +struct vfio_group *vfio_group_get_from_dev(struct device *dev) > >>> { > >>> struct iommu_group *iommu_group; > >>> struct vfio_group *group; > >>> @@ -494,6 +501,7 @@ static struct vfio_group *vfio_group_get_from_dev(struct device *dev) > >>> > >>> return group; > >>> } > >>> +EXPORT_SYMBOL_GPL(vfio_group_get_from_dev); > >>> > >>> /** > >>> * Device objects - create, release, get, put, search > >>> @@ -1745,6 +1753,44 @@ long vfio_external_check_extension(struct vfio_group *group, unsigned long arg) > >>> } > >>> EXPORT_SYMBOL_GPL(vfio_external_check_extension); > >>> > >>> +int vfio_group_register_notifier(struct vfio_group *group, struct notifier_block *nb) > >>> +{ > >>> + return blocking_notifier_chain_register(&group->udata.notifier, nb); > >>> +} > >>> +EXPORT_SYMBOL_GPL(vfio_group_register_notifier); > >>> + > >>> +int vfio_group_unregister_notifier(struct vfio_group *group, struct notifier_block *nb) > >>> +{ > >>> + return blocking_notifier_chain_unregister(&group->udata.notifier, nb); > >>> +} > >>> +EXPORT_SYMBOL_GPL(vfio_group_unregister_notifier); > >> > >> Kirti is already adding vfio_register_notifier & > >> vfio_unregister_notifier, these are not exclusive to the iommu, I > >> clarified that in my question that IOVA range invalidation is just one > >> aspect of what that notifier might be used for. The mdev framework > >> also automatically registers and unregisters that notifier around > >> open/release. So, I don't think we want a new notifier, we just want > >> vfio.c to also consume that notifier. > > > > Unfortunately the kvm:group attaching happens before device opening, > > so registering the notifier in open() is not functional: the event > > has disappeared before we start watching it. > > > > A possible workaround is, register the notifier in create() instead of > > open(). That should be functional, but will cause another issue: being able > > to register a notifier means we have a vfio-group reference, when to put > > that reference? putting it in remove() is not a good idea since a device > > might be open/release multiple times between create/remove, holding the ref > > until removal breaks it; putting it in release() is obviously not a > > good idea neither. > > > > IOW, having the notifiers there must be some dirty work in vendor > > driver to work around the issue above :( > > > >> So I think this patch needs a few components that build on what Kirti > >> has, 1) we add a blocking_notifier_head per vfio_group and have > >> vfio_{un}regsiter_notifier add and remove that notifier to the group > >> chain, 2) we create a vfio_group_notify() function that the kvm-vfio > >> pseudo device can call via symbol_get, 3) Have kvm-vfio call > >> vfio_group_notify() with VFIO_GROUP_NOTIFY_SET_KVM where the data is a > >> pointer to the struct kvm (or NULL to unset, we don't need separate set > >> vs unset notifiers). Does that work? Thanks, > > > > Yes, it works better than the original form of below patch. > > vfio side doesn't store any data, nor introduce any lock, only a callback > > for kvm to use. > > > > To make my reply clearer: the notifier can work without two separate > set/unset, can be combined with Kirti's iommu notifier, however, the problem > of being too late to register from open() still exists, and I still find it > difficult to work around. Ok, so it's a little bit ugly, but kvm-vfio can tell vfio about struct kvm with a vfio_group_set_kvm() callback that it uses via symbol get, using the real struct kvm pointer or NULL to unset. vfio caches this on the vfio_group. When a notifier is registered, it replays the event through the notifier. Any updates while a notifier is connected are both cached and immediately replayed through the notifier. So the vendor driver to vfio communication channel is the same, but the vfio to kvm-vfio involves some buffering. Does that work? Thanks, Alex