Re: remove the nvlink2 pci_vfio subdriver v2

Alex Williamson
2021-05-04T15:33:35Z

On Tue, 4 May 2021 16:11:31 +0200
Greg Kurz <groug@kaod.org> wrote:

> On Tue, 4 May 2021 15:30:15 +0200
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
>
> > On Tue, May 04, 2021 at 03:20:34PM +0200, Greg Kurz wrote:
> > > On Tue, 4 May 2021 14:59:07 +0200
> > > Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > >
> > > > On Tue, May 04, 2021 at 02:22:36PM +0200, Greg Kurz wrote:
> > > > > On Fri, 26 Mar 2021 07:13:09 +0100
> > > > > Christoph Hellwig <hch@lst.de> wrote:
> > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > the nvlink2 vfio subdriver is a weird beast. It supports a hardware
> > > > > > feature without any open source component - what would normally be
> > > > > > the normal open source userspace that we require for kernel drivers,
> > > > > > although in this particular case user space could of course be a
> > > > > > kernel driver in a VM. It also happens to be a complete mess that
> > > > > > does not properly bind to PCI IDs, is hacked into the vfio_pci driver
> > > > > > and also pulles in over 1000 lines of code always build into powerpc
> > > > > > kernels that have Power NV support enabled. Because of all these
> > > > > > issues and the lack of breaking userspace when it is removed I think
> > > > > > the best idea is to simply kill.
> > > > > >
> > > > > > Changes since v1:
> > > > > > - document the removed subtypes as reserved
> > > > > > - add the ACK from Greg
> > > > > >
> > > > > > Diffstat:
> > > > > > arch/powerpc/platforms/powernv/npu-dma.c | 705 ---------------------------
> > > > > > b/arch/powerpc/include/asm/opal.h | 3
> > > > > > b/arch/powerpc/include/asm/pci-bridge.h | 1
> > > > > > b/arch/powerpc/include/asm/pci.h | 7
> > > > > > b/arch/powerpc/platforms/powernv/Makefile | 2
> > > > > > b/arch/powerpc/platforms/powernv/opal-call.c | 2
> > > > > > b/arch/powerpc/platforms/powernv/pci-ioda.c | 185 -------
> > > > > > b/arch/powerpc/platforms/powernv/pci.c | 11
> > > > > > b/arch/powerpc/platforms/powernv/pci.h | 17
> > > > > > b/arch/powerpc/platforms/pseries/pci.c | 23
> > > > > > b/drivers/vfio/pci/Kconfig | 6
> > > > > > b/drivers/vfio/pci/Makefile | 1
> > > > > > b/drivers/vfio/pci/vfio_pci.c | 18
> > > > > > b/drivers/vfio/pci/vfio_pci_private.h | 14
> > > > > > b/include/uapi/linux/vfio.h | 38 -
> > > > >
> > > > >
> > > > > Hi Christoph,
> > > > >
> > > > > FYI, these uapi changes break build of QEMU.
> > > >
> > > > What uapi changes?
> > > >
> > >
> > > All macros and structure definitions that are being removed
> > > from include/uapi/linux/vfio.h by patch 1.
> > >
> > > > What exactly breaks?
> > > >
> > >
> > > These macros and types are used by the current QEMU code base.
> > > Next time the QEMU source tree updates its copy of the kernel
> > > headers, the compilation of affected code will fail.
> >
> > So does QEMU use this api that is being removed, or does it just have
> > some odd build artifacts of the uapi things?
> >
>
> These are region subtypes definition and associated capabilities.
> QEMU basically gets information on VFIO regions from the kernel
> driver and for those regions with a nvlink2 subtype, it tries
> to extract some more nvlink2 related info.

Urgh, let's put the uapi header back in place with a deprecation
notice. Userspace should never have a dependency on the existence of a
given region, but clearly will have code to parse the data structure
describing that region. I'll post a patch. Thanks,

Alex