Am 15.11.2018 um 16:47 schrieb Will Deacon [off-list ref]:

quoted

On Tue, Nov 13, 2018 at 04:29:06PM +0100, Alexander Graf wrote:
I've already stumbled over 2 cases where people got confused about how to
disable kpti on AArch64. In both cases, they used existing x86_64 options
and just applied that to an AArch64 system, expecting it to work.

I think it makes a lot of sense to have compatible kernel command line
parameters whenever we can have them be compatible.

So this patch adds the pti= and no_pti kernel command line options, mapping
them into the existing kpti= command line framework. It preserves the old
syntax to maintain compatibility with older command lines.

While at it, the patch also marks the respective options as dual-arch.

Reported-by: Richard Brown <redacted>
Signed-off-by: Alexander Graf <redacted>

---

v1 -> v2:

 - Actually make it compile. Sorry for the sloppy v1.
---
Documentation/admin-guide/kernel-parameters.txt |  6 +++---
arch/arm64/kernel/cpufeature.c                  | 20 +++++++++++++++++++-
2 files changed, 22 insertions(+), 4 deletions(-)

This patch doesn't help though, right, because kpti= has already been
included with backports etc so the ship has sailed?

Not necessarily. We can always mark this as stable and have distros pull it in. Consistency is definitely useful for everyone.

Yeah, it's not ideal,
but we went over this before:

http://lists.infradead.org/pipermail/linux-arm-kernel/2018-August/598395.html

Ah, I mist havd missed that. But if you already have 2 people sending very similar patches, there is probably something to it :).

The thing we really need is the sysfs interface hooking up so you can easily
check the state of the mitigation. Still waiting for a follow-up on that ;)

http://lists.infradead.org/pipermail/linux-arm-kernel/2018-September/603412.html

That one is very much needed as well, yes.

Alex

Will