Re: [RFC][PATCH 05/17] x86/cpu: Cleanup the untrain mess

From: Peter Zijlstra
Date: Wed Aug 09 2023 - 09:12:54 EST


On Wed, Aug 09, 2023 at 08:51:01AM -0400, Josh Poimboeuf wrote:
> On Wed, Aug 09, 2023 at 09:12:23AM +0200, Peter Zijlstra wrote:
> > Since there can only be one active return_thunk, there only needs be
> > one (matching) untrain_ret. It fundamentally doesn't make sense to
> > allow multiple untrain_ret at the same time.
> >
> > Fold all the 3 different untrain methods into a single (temporary)
> > helper stub.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> > arch/x86/include/asm/nospec-branch.h | 19 +++++--------------
> > arch/x86/lib/retpoline.S | 7 +++++++
> > 2 files changed, 12 insertions(+), 14 deletions(-)
> >
> > --- a/arch/x86/include/asm/nospec-branch.h
> > +++ b/arch/x86/include/asm/nospec-branch.h
> > @@ -272,9 +272,9 @@
> > .endm
> >
> > #ifdef CONFIG_CPU_UNRET_ENTRY
> > -#define CALL_ZEN_UNTRAIN_RET "call zen_untrain_ret"
> > +#define CALL_UNTRAIN_RET "call entry_untrain_ret"
> > #else
> > -#define CALL_ZEN_UNTRAIN_RET ""
> > +#define CALL_UNTRAIN_RET ""
> > #endif
> >
> > /*
> > @@ -293,15 +293,10 @@
> > defined(CONFIG_CALL_DEPTH_TRACKING) || defined(CONFIG_CPU_SRSO)
> > VALIDATE_UNRET_END
> > ALTERNATIVE_3 "", \
> > - CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET, \
> > + CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \
>
> SRSO doesn't have X86_FEATURE_UNRET set.

Argh.. this stuff doesn't exist at the end anymore, but yeah, that's
unfortunate.

I'll see if I can find another intermediate step.