[Intel-gfx] [PATCH v2 00/10] Introduce new methods for verifying ownership in vfio PCI hot reset

[Jiang, Yanting]

> -----Original Message-----
> From: Alex Williamson <alex.williamson at redhat.com>
> Sent: Friday, March 31, 2023 9:25 PM
> To: Jiang, Yanting <yanting.jiang at intel.com>
> Cc: Liu, Yi L <yi.l.liu at intel.com>; jgg at nvidia.com; Tian, Kevin
> <kevin.tian at intel.com>; joro at 8bytes.org; robin.murphy at arm.com;
> cohuck at redhat.com; eric.auger at redhat.com; nicolinc at nvidia.com;
> kvm at vger.kernel.org; mjrosato at linux.ibm.com; chao.p.peng at linux.intel.com;
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> suravee.suthikulpanit at amd.com; intel-gvt-dev at lists.freedesktop.org; intel-
> gfx at lists.freedesktop.org; linux-s390 at vger.kernel.org; Hao, Xudong
> <xudong.hao at intel.com>; Zhao, Yan Y <yan.y.zhao at intel.com>; Xu, Terrence
> <terrence.xu at intel.com>
> Subject: Re: [PATCH v2 00/10] Introduce new methods for verifying ownership in
> vfio PCI hot reset
> 
> On Fri, 31 Mar 2023 03:14:23 +0000
> "Jiang, Yanting" <yanting.jiang at intel.com> wrote:
> 
> > >
> > > VFIO_DEVICE_PCI_HOT_RESET requires user to pass an array of group
> > > fds to prove that it owns all devices affected by resetting the
> > > calling device. This series introduces several extensions to allow
> > > the ownership check better aligned with iommufd and coming vfio device
> cdev support.
> > >
> > > First, resetting an unopened device is always safe given nobody is
> > > using it. So relax the check to allow such devices not covered by
> > > group fd array. [1]
> > >
> > > When iommufd is used we can simply verify that all affected devices
> > > are bound to a same iommufd then no need for the user to provide extra fd
> information.
> > > This is enabled by the user passing a zero-length fd array and
> > > moving forward this should be the preferred way for hot reset. [2]
> > >
> > > However the iommufd method has difficulty working with noiommu
> > > devices since those devices don't have a valid iommufd, unless the
> > > noiommu device is in a singleton dev_set hence no ownership check is
> > > required. [3]
> > >
> > > For noiommu backward compatibility a 3rd method is introduced by
> > > allowing the user to pass an array of device fds to prove ownership.
> > > [4]
> > >
> > > As suggested by Jason [5], we have this series to introduce the
> > > above stuffs to the vfio PCI hot reset. Per the dicussion in [6],
> > > this series also adds a new _INFO ioctl to get hot reset scope for given
> device.
> > >
> > Tested NIC passthrough on Intel platform.
> > Result looks good hence,
> > Tested by: Jiang, Yanting <yanting.jiang at intel.com>
> 
> I'm not aware of any userspace that exercises this reset ioctl in cdev mode.  Is
> this regression testing only?  Thanks,
> 
> Alex

Hi Alex, 

Yes, only regression testing and some negative testing for NIC passthrough with legacy vfio mode, vfio iommufd compat mode, and cdev mode.

Thanks,
Yanting