Re: remove the nvlink2 pci_vfio subdriver v2

Re: remove the nvlink2 pci_vfio subdriver v2

[Greg Kurz]

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.

I guess QEMU people should take some action before this percolates
to the QEMU source tree.

Cc'ing relevant QEMU lists to bring the discussion there.

Cheers,

--
Greg

>  drivers/vfio/pci/vfio_pci_nvlink2.c          |  490 ------------------
>  16 files changed, 12 insertions(+), 1511 deletions(-)

Re: remove the nvlink2 pci_vfio subdriver v2

[Greg Kroah-Hartman]

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?

What exactly breaks?

Why does QEMU require kernel driver stuff?

thanks,

greg k-h

Re: remove the nvlink2 pci_vfio subdriver v2

[Christoph Hellwig]

On Tue, May 04, 2021 at 02:59:07PM +0200, Greg Kroah-Hartman wrote:
> > Hi Christoph,
> > 
> > FYI, these uapi changes break build of QEMU.
> 
> What uapi changes?
> 
> What exactly breaks?
> 
> Why does QEMU require kernel driver stuff?

Looks like it pull in the uapi struct definitions unconditionally
instead of having a local copy.  We could fix that by just putting
them back, but to me this seems like a rather broken configuration
in qemu when it pulls in headers from the running/installed kernel
without any feature checks before using them.

Re: remove the nvlink2 pci_vfio subdriver v2

[Cornelia Huck]

On Tue, 4 May 2021 15:00:39 +0200
Christoph Hellwig <hch@lst.de> wrote:

> On Tue, May 04, 2021 at 02:59:07PM +0200, Greg Kroah-Hartman wrote:
> > > Hi Christoph,
> > > 
> > > FYI, these uapi changes break build of QEMU.  
> > 
> > What uapi changes?
> > 
> > What exactly breaks?
> > 
> > Why does QEMU require kernel driver stuff?  
> 
> Looks like it pull in the uapi struct definitions unconditionally
> instead of having a local copy.  We could fix that by just putting
> them back, but to me this seems like a rather broken configuration
> in qemu when it pulls in headers from the running/installed kernel
> without any feature checks before using them.
> 

It is not pulling them from the installed kernel, but from a
development version to get new definitions. Removing things in the
kernel requires workarounds in QEMU until it can remove those things as
well. It is not a dumb update...

Re: remove the nvlink2 pci_vfio subdriver v2

[Greg Kurz]

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.

> Why does QEMU require kernel driver stuff?
> 

Not sure to understand the question... is there a problem
with QEMU using an already published uapi ?

> thanks,
> 
> greg k-h

Re: remove the nvlink2 pci_vfio subdriver v2

[Greg Kroah-Hartman]

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?

What exactly is the error messages here?

And if we put the uapi .h file stuff back, is that sufficient for qemu
to work, as it should be checking at runtime what the kernel has / has
not anyway, right?

thanks,

greg k-h

Re: remove the nvlink2 pci_vfio subdriver v2

[Greg Kurz]

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.

> What exactly is the error messages here?
> 

[55/143] Compiling C object libqemu-ppc64-softmmu.fa.p/hw_vfio_pci-quirks.c.o
FAILED: libqemu-ppc64-softmmu.fa.p/hw_vfio_pci-quirks.c.o 
cc -Ilibqemu-ppc64-softmmu.fa.p -I. -I../.. -Itarget/ppc -I../../target/ppc -I../../capstone/include/capstone -Iqapi -Itrace -Iui -Iui/shader -I/usr/include/pixman-1 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -fdiagnostics-color=auto -pipe -Wall -Winvalid-pch -Werror -std=gnu99 -O2 -g -isystem /home/greg/Work/qemu/qemu-virtiofs/linux-headers -isystem linux-headers -iquote . -iquote /home/greg/Work/qemu/qemu-virtiofs -iquote /home/greg/Work/qemu/qemu-virtiofs/include -iquote /home/greg/Work/qemu/qemu-virtiofs/disas/libvixl -iquote /home/greg/Work/qemu/qemu-virtiofs/tcg/ppc -iquote /home/greg/Work/qemu/qemu-virtiofs/accel/tcg -pthread -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv -Wold-style-declaration -Wold-style-definition -Wtype-limits -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs -Wendif-labels -Wexpansion-to-defined -Wimplicit-fallthrough=2 -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-psabi -fstack-protector-strong -fPIC -isystem../../linux-headers -isystemlinux-headers -DNEED_CPU_H '-DCONFIG_TARGET="ppc64-softmmu-config-target.h"' '-DCONFIG_DEVICES="ppc64-softmmu-config-devices.h"' -MD -MQ libqemu-ppc64-softmmu.fa.p/hw_vfio_pci-quirks.c.o -MF libqemu-ppc64-softmmu.fa.p/hw_vfio_pci-quirks.c.o.d -o libqemu-ppc64-softmmu.fa.p/hw_vfio_pci-quirks.c.o -c ../../hw/vfio/pci-quirks.c
../../hw/vfio/pci-quirks.c: In function ‘vfio_pci_nvidia_v100_ram_init’:
../../hw/vfio/pci-quirks.c:1597:36: error: ‘VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM’ undeclared (first use in this function); did you mean ‘VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD’?
                                    VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM,
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                    VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD
../../hw/vfio/pci-quirks.c:1597:36: note: each undeclared identifier is reported only once for each function it appears in
../../hw/vfio/pci-quirks.c:1603:44: error: ‘VFIO_REGION_INFO_CAP_NVLINK2_SSATGT’ undeclared (first use in this function); did you mean ‘VFIO_REGION_INFO_CAP_SPARSE_MMAP’?
     hdr = vfio_get_region_info_cap(nv2reg, VFIO_REGION_INFO_CAP_NVLINK2_SSATGT);
                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                            VFIO_REGION_INFO_CAP_SPARSE_MMAP
../../hw/vfio/pci-quirks.c:1624:49: error: dereferencing pointer to incomplete type ‘struct vfio_region_info_cap_nvlink2_ssatgt’
                         (void *) (uintptr_t) cap->tgt);
                                                 ^~
../../hw/vfio/pci-quirks.c: In function ‘vfio_pci_nvlink2_init’:
../../hw/vfio/pci-quirks.c:1646:36: error: ‘VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD’ undeclared (first use in this function); did you mean ‘VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD’?
                                    VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD,
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                    VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD
../../hw/vfio/pci-quirks.c:1653:36: error: ‘VFIO_REGION_INFO_CAP_NVLINK2_SSATGT’ undeclared (first use in this function); did you mean ‘VFIO_REGION_INFO_CAP_SPARSE_MMAP’?
                                    VFIO_REGION_INFO_CAP_NVLINK2_SSATGT);
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                    VFIO_REGION_INFO_CAP_SPARSE_MMAP
../../hw/vfio/pci-quirks.c:1661:36: error: ‘VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD’ undeclared (first use in this function); did you mean ‘VFIO_REGION_INFO_CAP_SPARSE_MMAP’?
                                    VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD);
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                    VFIO_REGION_INFO_CAP_SPARSE_MMAP
../../hw/vfio/pci-quirks.c:1685:52: error: dereferencing pointer to incomplete type ‘struct vfio_region_info_cap_nvlink2_ssatgt’
                         (void *) (uintptr_t) captgt->tgt);
                                                    ^~
../../hw/vfio/pci-quirks.c:1691:54: error: dereferencing pointer to incomplete type ‘struct vfio_region_info_cap_nvlink2_lnkspd’
                         (void *) (uintptr_t) capspeed->link_speed);
                                                      ^~

> And if we put the uapi .h file stuff back, is that sufficient for qemu
> to work, as it should be checking at runtime what the kernel has / has
> not anyway, right?
> 

Right. This will just be dead code in QEMU for newer kernels.

Anyway, as said in some other mail, it is probably time for QEMU to
start deprecating this code as well.

> thanks,
> 
> greg k-h

Re: remove the nvlink2 pci_vfio subdriver v2

[Alex Williamson]

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

Re: remove the nvlink2 pci_vfio subdriver v2

[Daniel Vetter]

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.

Just my 2cents from drm (where we deprecate old gunk uapi quite often):
Imo it's best to keep the uapi headers as-is, but exchange the
documentation with a big "this is removed, never use again" warning:

- it occasionally serves as a good lesson for how to not do uapi (whatever
  the reasons really are in the specific case)

- it's good to know which uapi numbers (like parameter extensions or
  whatever they are in this case) are defacto reserved, because there are
  binaries (qemu in this) that have code acting on them out there.

The only exception where we completely nuke the structs and #defines is
when uapi has been only used by testcases. Which we know, since we defacto
limit our stable uapi guarantee to the canonical open&upstream userspace
drivers only (for at least the driver-specific stuff, the cross-driver
interfaces are hopeless).

Anyway feel free to ignore since this might be different than drivers/gpu.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: remove the nvlink2 pci_vfio subdriver v2

[Jason Gunthorpe]

On Tue, May 04, 2021 at 04:23:40PM +0200, Daniel Vetter wrote:

> Just my 2cents from drm (where we deprecate old gunk uapi quite often):
> Imo it's best to keep the uapi headers as-is, but exchange the
> documentation with a big "this is removed, never use again" warning:

We in RDMA have been doing the opposite, the uapi headers are supposed
to reflect the current kernel. This helps make the kernel
understandable.

When userspace needs backwards compat to ABI that the current kernel
doesn't support then userspace has distinct copies of that information
in some compat location. It has happened a few times over the last 15
years.

We keep full copies of the current kernel headers in the userspace
source tree, when the kernel headers change in a compile incompatible
way we fix everything while updating to the new kernel headers.

> - it's good to know which uapi numbers (like parameter extensions or
>   whatever they are in this case) are defacto reserved, because there are
>   binaries (qemu in this) that have code acting on them out there.

Numbers and things get marked reserved or the like

> Anyway feel free to ignore since this might be different than drivers/gpu.

AFAIK drives/gpu has a lot wider userspace, rdma manages this OK
because we only have one library package that provides the user/kernel
interface.
 
Jason

Re: remove the nvlink2 pci_vfio subdriver v2

[Daniel Vetter]

On Tue, May 04, 2021 at 12:53:27PM -0300, Jason Gunthorpe wrote:
> On Tue, May 04, 2021 at 04:23:40PM +0200, Daniel Vetter wrote:
> 
> > Just my 2cents from drm (where we deprecate old gunk uapi quite often):
> > Imo it's best to keep the uapi headers as-is, but exchange the
> > documentation with a big "this is removed, never use again" warning:
> 
> We in RDMA have been doing the opposite, the uapi headers are supposed
> to reflect the current kernel. This helps make the kernel
> understandable.
> 
> When userspace needs backwards compat to ABI that the current kernel
> doesn't support then userspace has distinct copies of that information
> in some compat location. It has happened a few times over the last 15
> years.
> 
> We keep full copies of the current kernel headers in the userspace
> source tree, when the kernel headers change in a compile incompatible
> way we fix everything while updating to the new kernel headers.

Yeah we do the same since forever (it's either from libdrm package, or
directly in the corresponding userspace header). So largely include/uapi
is for documentation

> > - it's good to know which uapi numbers (like parameter extensions or
> >   whatever they are in this case) are defacto reserved, because there are
> >   binaries (qemu in this) that have code acting on them out there.
> 
> Numbers and things get marked reserved or the like
> 
> > Anyway feel free to ignore since this might be different than drivers/gpu.
> 
> AFAIK drives/gpu has a lot wider userspace, rdma manages this OK
> because we only have one library package that provides the user/kernel
> interface.

But since we have some many projects we've started asking all the userspace
projects to directly take the kernel ones (after the make step to filter
them) so that there's only one source of truth. And also to make sure they
don't merge stuff before the kernel side is reviewed&landed. Which also
means we can't ditch anything userspace might still need on older trees
and stuff.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch