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

Tom Rini trini at konsulko.com
Tue Feb 7 17:40:05 CET 2023

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:

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.

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