From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jike Song Subject: Re: [v3 4/5] vfio: implement APIs to set/put kvm to/from vfio group Date: Thu, 10 Nov 2016 12:10:18 +0800 Message-ID: <5823F32A.7040807@intel.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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: Alex Williamson Return-path: Received: from mga11.intel.com ([192.55.52.93]:29273 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753108AbcKJEN5 (ORCPT ); Wed, 9 Nov 2016 23:13:57 -0500 In-Reply-To: <20161109105352.3337acbb@t450s.home> Sender: kvm-owner@vger.kernel.org List-ID: 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. -- Thanks, Jike