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Date: Wed, 18 May 2022 12:12:47 -0300 From: Jason Gunthorpe <jgg@...dia.com> To: Matthew Rosato <mjrosato@...ux.ibm.com> Cc: alex.williamson@...hat.com, cohuck@...hat.com, borntraeger@...ux.ibm.com, jjherne@...ux.ibm.com, akrowiak@...ux.ibm.com, pasic@...ux.ibm.com, zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, hch@...radead.org, intel-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org, linux-s390@...r.kernel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM On Wed, May 18, 2022 at 10:37:48AM -0400, Matthew Rosato wrote: > On 5/17/22 2:08 PM, Matthew Rosato wrote: > > Rather than relying on a notifier for associating the KVM with > > the group, let's assume that the association has already been > > made prior to device_open. The first time a device is opened > > associate the group KVM with the device. > > > > Suggested-by: Jason Gunthorpe <jgg@...dia.com> > > Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com> > > ... > > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > > index cfcff7764403..c5d421eda275 100644 > > +++ b/drivers/vfio/vfio.c > > @@ -10,6 +10,7 @@ > > * Author: Tom Lyon, pugs@...co.com > > */ > > +#include "linux/kvm_host.h" > > #include <linux/cdev.h> > > #include <linux/compat.h> > > #include <linux/device.h> > > @@ -1083,6 +1084,13 @@ static struct file *vfio_device_open(struct vfio_device *device) > > mutex_lock(&device->dev_set->lock); > > device->open_count++; > > + down_write(&device->group->group_rwsem); > > + if (device->open_count == 1 && device->group->kvm) { > > + device->kvm = device->group->kvm; > > + kvm_get_kvm(device->kvm); > > Did some more compile testing, since vfio has no hard kvm dependency, > kvm_get_kvm and kvm_put_kvm are an issue if KVM is a module while vfio is > built-in... Ugh, my other plan was to have the driver itself capture the kvm, ie we lock the group_rwsem to keep the group->kvm valid and then pass the kvm to open_device in some way, then the driver can kvm_get_kvm() it Alternatively, I don't know why kvm_get_kvm() is an exported symbol when it is just calling refcount_inc() - inlining it would be an improvement I think. Jason
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