* Peter Zijlstra <[email protected]> wrote:
> On Mon, Jan 08, 2018 at 06:05:31PM +0100, Ingo Molnar wrote:
> > Note that there is somewhat of a fuzzy detail regarding AMD CPUs which are
> > marked
> > as 'Meltdown safe': should an explicit request to turn on PTI be honored by
> > the
> > kernel? Should that be some sort of separate 'force PTI on' attribute?
>
> AMD should not have FEATURE_PTI enabled, and thus not end up in any code
> that cares about TIF_NOPTI.
I know, this is the status quo.
Nevertheless:
- if someone disbelieves AMD's claims and wants to force-enable it, should it
be
possible without patching the kernel?
- or if someone wants to test it on AMD to increase test coverage. pti=on will
already be force-enable it on AMD CPUs.
Likewise, there's the counter part on the app level PTI disabling/enabling
ABI functionality as well:
- should there be a way for sysadmins to force PTI enabled, even on apps that
want to turn it off?
- should there be a way for sysadmins to force PTI disabled, even for apps
that
want to turn it on?
If we decide that we want to allow fine-grained, per app control of PTI, then
all
of these look valid scenarios to me.
Thanks,
Ingo
