[PATCH 1/2] arm: cpu: Add optional CMOs by VA

[Marc Zyngier]

On Tue, 07 Feb 2023 16:40:05 +0000,
Tom Rini <trini at konsulko.com> wrote:
> 
> On Tue, Feb 07, 2023 at 04:35:25PM +0000, Marc Zyngier wrote:
> > On 2023-02-07 16:20, Ying-Chun Liu (PaulLiu) wrote:
> > > Exposing set/way cache maintenance to a virtual machine is unsafe, not
> > > least because the instructions are not permission-checked but also
> > > because they are not broadcast between CPUs. Consequently, KVM traps and
> > > emulates such maintenance in the host kernel using by-VA operations and
> > > looping over the stage-2 page-tables. However, when running under
> > > protected KVM, these instructions are not able to be emulated and will
> > > instead result in an exception being delivered to the guest.
> > > 
> > > Introduce CONFIG_CMO_BY_VA_ONLY so that virtual platforms can select
> > > this option and perform by-VA cache maintenance instead of using the
> > > set/way instructions.
> > > 
> > > Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu at linaro.org>
> > > Signed-off-by: Marc Zyngier <maz at kernel.org>
> > > Signed-off-by: Will Deacon <willdeacon at google.com>
> > > Cc: Tom Rini <trini at konsulko.com>
> > 
> > The sign-off chain looks pretty odd. Either you are the author
> > of this patch, and I have nothing to do on the sign-off list,
> > or I'm the author and the authorship is wrong. Similar things
> > would apply for Will.
> > 
> > So which one is it?
> 
> As my first guess here is copy and adopting code from Linux, this is
> not following the documented procedure here:
> https://u-boot.readthedocs.io/en/latest/develop/sending_patches.html#attributing-code-copyrights-signing
>
> Which if not sufficiently clear, please ask / suggest changes to. I see
> right now it isn't specific about cc'ing the original authors (who may,
> or may not, be interested, so blanket policy doesn't apply) but I would
> hope is clear enough that what's done in this example isn't right.

No, this really is u-boot code written as part of Android, from where
the patch has been directly lifted[1].

Same goes for Pierre-Clement's patch that is part of the same series.

I'm not overly attached to this code (I have bad memories from it),
but I think the OP may be unaware of these rules. In any case, I'm
supportive of this code making it in upstream u-boot. I just want it
to be done correctly.

Thanks,

	M.

[1] https://android.googlesource.com/platform/external/u-boot/+/db5507f47f4f57f766d52f753ff2cc761afc213b

-- 
Without deviation from the norm, progress is not possible.