On Wed, Sep 22, 2021 at 01:07:11AM +0000, Tian, Kevin wrote: > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > Sent: Wednesday, September 22, 2021 8:55 AM > > > > On Tue, Sep 21, 2021 at 11:56:06PM +0000, Tian, Kevin wrote: > > > > The opened atomic is aweful. A newly created fd should start in a > > > > state where it has a disabled fops > > > > > > > > The only thing the disabled fops can do is register the device to the > > > > iommu fd. When successfully registered the device gets the normal fops. > > > > > > > > The registration steps should be done under a normal lock inside the > > > > vfio_device. If a vfio_device is already registered then further > > > > registration should fail. > > > > > > > > Getting the device fd via the group fd triggers the same sequence as > > > > above. > > > > > > > > > > Above works if the group interface is also connected to iommufd, i.e. > > > making vfio type1 as a shim. In this case we can use the registration > > > status as the exclusive switch. But if we keep vfio type1 separate as > > > today, then a new atomic is still necessary. This all depends on how > > > we want to deal with vfio type1 and iommufd, and possibly what's > > > discussed here just adds another pound to the shim option... > > > > No, it works the same either way, the group FD path is identical to > > the normal FD path, it just triggers some of the state transitions > > automatically internally instead of requiring external ioctls. > > > > The device FDs starts disabled, an internal API binds it to the iommu > > via open coding with the group API, and then the rest of the APIs can > > be enabled. Same as today. > > > > Still a bit confused. if vfio type1 also connects to iommufd, whether > the device is registered can be centrally checked based on whether > an iommu_ctx is recorded. But if type1 doesn't talk to iommufd at > all, don't we still need introduce a new state (calling it 'opened' or > 'registered') to protect the two interfaces? The "new state" is if the fops are pointing at the real fops or the pre-fops, which in turn protects everything. You could imagine this as some state in front of every fop call if you want. > In this case what is the point of keeping device FD disabled even > for the group path? I have a feeling when you go through the APIs it will make sense to have some symmetry here. eg creating a device FD should have basically the same flow no matter what triggers it, not confusing special cases where the group code skips steps Jason
