linux-kernel - Re: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN

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Message-ID: <CAPZXPQe+MPTGD3MH1HORvCZa08HhdbWy=zh7rLSCwA6edM2Ccg@mail.gmail.com>
Date:   Fri, 19 Aug 2022 14:33:32 +0300
From:   Martin-Éric Racine <martin-eric.racine@....fi>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ben Hutchings <ben@...adent.org.uk>, x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        1017425@...s.debian.org, stable@...r.kernel.org,
        regressions@...ts.linux.dev,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Subject: Re: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN_BUFFER on
 CPUs that lack it

On Fri, Aug 19, 2022 at 2:01 PM Peter Zijlstra <peterz@...radead.org> wrote:
> I'm not entirly sure what to do here. On the one hand, it's 32bit, so
> who gives a crap, otoh we shouldn't break these ancient chips either I
> suppose.

This is something that I've repeatedly had to bring up, whenever
something breaks because someone meant well by enabling more security
bells and whistles:

x86-32 is by definition legacy hardware. Enabling more bells and
whistles essentially kills support for all but the very latest
variants of the x86-32 family. This is the wrong approach. The right
approach is to accept that building for x86-32 inherently means
building for older and thus less secure architectures.

Martin-Éric