linux-kernel - Re: Bug#1017425: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN

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Date:   Tue, 30 Aug 2022 15:35:27 +0200
From:   Salvatore Bonaccorso <carnil@...ian.org>
To:     martin-eric.racine@....fi, 1017425@...s.debian.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ben Hutchings <ben@...adent.org.uk>, x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.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: Bug#1017425: [PATCH] x86/speculation: Avoid LFENCE in
 FILL_RETURN_BUFFER on CPUs that lack it

Hi Martin,

On Tue, Aug 30, 2022 at 03:18:51PM +0300, Martin-??ric Racine wrote:
> On Tue, Aug 30, 2022 at 3:00 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, Aug 30, 2022 at 02:42:04PM +0300, Martin-??ric Racine wrote:
> > > On Fri, Aug 19, 2022 at 3:15 PM Peter Zijlstra <peterz@...radead.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?
> >
> > https://git.kernel.org/tip/332924973725e8cdcc783c175f68cf7e162cb9e5
> 
> Thanks.
> 
> Ben: When can we expect an updated kernel to security-updates at Debian?

When the update is ready to go. Likely the update for the next point
release for bullseye will contain the fix for this issue.

Regards,
Salvatore