Bug#1017425: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN_BUFFER on CPUs that lack it

[Martin-Éric Racine <martin-eric.racine@iki.fi>]

Greetings,

On Fri, Aug 19, 2022 at 3:15 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Aug 19, 2022 at 01:38:27PM +0200, Ben Hutchings wrote:
>
> > So that puts the whole __FILL_RETURN_BUFFER inside an alternative, and
> > we can't have nested alternatives.  That's unfortunate.
>
> Well, both alternatives end with the LFENCE instruction, so I could pull
> it out and do two consequtive ALTs, but unrolling the loop for i386 is
> a better solution in that the sequence, while larger, removes the need
> for the LFENCE.

Have we reached a definitive conclusion on to how to fix this?

Martin-Éric