Re: x86/pkeys in early kernel version

[Jeff Xu <jeffxu@chromium.org>]

On Wed, Jan 25, 2023 at 5:43 PM Jeff Xu <jeffxu@chromium.org> wrote:
>
> On Wed, Jan 25, 2023 at 11:13 AM Dave Hansen <dave.hansen@intel.com> wrote:
> >
> > On 1/25/23 11:02, Jeff Xu wrote:
> > > I'm investigating if there is a need to backport x86/pkeys
> > > fix/feature into earlier kernel versions, Chrome is starting to use
> > > PKEY in x86, and I hope experts here can give advice on this.
> > >
> > > For background, ChromeOS regularly syncs with upstream kernel
> > > versions, and has production that uses 4.4/4.14/4.19/5.4/5.10/5.15.
> > To be honest, I haven't got the foggiest idea what you need to backport.
> >  I can barely keep track of mainline.
> >
> > Are there really production 4.4 kernels that you need to run on
> > pkey-capable hardware?  That would mean running a 2015-era kernel on a
> > CPU released in late 2020.  I think Q3'2020 is when the 11th gen CPUs
> > came out which were the first non-server CPUs that had pkeys.
> >
> Thanks!
> For 11th gen CPUs, chromebook uses 5.4 and above, so that eliminate
> half of the versions.
>
> > On a positive note, the pkeys selftest has been pretty consistently
> > updated as we find bugs.  I'd be curious how well a mainline version of
> > that selftests runs on old kernels.  But, I'm too scared to find out
> > what's down that particular rabbit hole myself.
>
I took the latest selftest from main and run on 5.15 kernel,
all passed except test_ptrace_modifies_pkru
assert() at protection_keys.c::1623 test_nr: 20 iteration: 1

Is there a bugfix for the ptrace area ?
Thanks




> I can start with 5.10 or 5.15, it seems there are quite some changes though,
> for example,  this one by Thomas
> https://lore.kernel.org/lkml/20210623120127.327154589@linutronix.de/
>
> My question is, if I have to pick a version that doesn't require a lot
> of backporting,
> and functionality is stable enough, what version would this be ? 5.4/5.10/5.15 ?
>
> -Jeff