Re: [PATCH v2 01/17] arm: Placeholder for handling Group0/1 traps

[Stefano Stabellini <sstabellini@kernel.org>]

On Tue, 27 Mar 2018, Marc Zyngier wrote:
> On 27/03/18 11:10, Manish Jaggi wrote:
> > 
> > 
> > On 03/27/2018 03:31 PM, Marc Zyngier wrote:
> >> On 27/03/18 10:07, Manish Jaggi wrote:
> >>> The errata will require to emulate the GIC virtual CPU interface in Xen.
> >>> Because the hypervisor will update its internal state of the vGIC, we want
> >>> to avoid messing up with it. So the errata is handled separately from the
> >>> rest of the hypervisor.
> >>>
> >>> New file vgic-v3-sr.c is added which will hold trap and emulate code
> >>> for group0 / group1 registers. Workaround for cavium Errata 30115
> >>> needs this emulation code.
> >>>
> >>> vgic_v3_handle_cpuif_access would be called from do_trap_guest_sync
> >>> in subsequent patches based on errata macros.
> >>>
> >>> Signed-off-by: Manish Jaggi <manish.jaggi@cavium.com>
> >>> ---
> >>>   xen/arch/arm/arm64/vgic-v3-sr.c   | 60 +++++++++++++++++++++++++++++++++++++++
> >>>   xen/include/asm-arm/arm64/traps.h |  2 ++
> >>>   2 files changed, 62 insertions(+)
> >>>   create mode 100644 xen/arch/arm/arm64/vgic-v3-sr.c
> >>>
> >>> diff --git a/xen/arch/arm/arm64/vgic-v3-sr.c b/xen/arch/arm/arm64/vgic-v3-sr.c
> >>> new file mode 100644
> >>> index 0000000000..39ab1ed6ca
> >>> --- /dev/null
> >>> +++ b/xen/arch/arm/arm64/vgic-v3-sr.c
> >>> @@ -0,0 +1,60 @@
> >>> +/*
> >>> + * xen/arch/arm/arm64/vgic-v3-sr.c
> >>> + *
> >>> + * Code to emulate group0/group1 traps for handling
> >>> + * cavium erratum 30115
> >>> + *
> >>> + * Manish Jaggi <manish.jaggi@cavium.com>
> >>> + * Copyright (c) 2018 Cavium.
> >> IANAL, but I don't think this copyright notice is correct.
> >>
> >> I wrote about 90% of this series, and the copyright for that code is
> >> owned by ARM, and licensed under the GPLv2. You have the right to
> >> duplicate that code and do almost whatever you want with (within the
> >> limits of the GPLv2), but you still don't own the copyright.
> >>
> >> I suggest you get in touch with your legal department for clarification
> >> on the matter.
> > I will remove the copyright line, and add this
> > Original Author: Marc Zyngier <>
> > Ported to Xen by: Manish Jaggi <>
> 
> You're missing the point. I don't give a damn about the authorship (I'm
> not exactly proud to have written that code).

:-D

> The problem at hand is the
> ARM copyright, which should be preserved (as no-one in Cavium wrote a
> single line of the original code).

I have been asking myself similar questions for a while now when we
import code from Linux. The copyright/author line at the top of the file
is somewhat arbitrary as every person that touched the code has
copyright over her modifications. This is why at some point I thought we
had to retain the full list of Signed-off-by lines that ever touched the
code in question, but then, reading the DCO terms one more time:

 (b) The contribution is based upon previous work that, to the best
     of my knowledge, is covered under an appropriate open source
     license and I have the right under that license to submit that
     work with modifications, whether created in whole or in part
     by me, under the same open source license (unless I am
     permitted to submit under a different license), as indicated
     in the file; or

I checked in the Linux kernel when code was imported from the Xen
hypervisor to KVM a long time ago, and only a singled Signed-off-by of
the person importing the code was used.

This is how I came to the conclusion that actually we don't need to do
anything special, although it would be nice as a courtesy to retain the
copyright/author lines at the top of the file. It would also be nice to
have the original Linux commit id in the commit message to help tracking
the history.

But I would love to have a clear guideline on this from a lawyer.

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