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Date:   Fri, 19 Aug 2022 10:47:21 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ben Hutchings <ben@decadent.org.uk>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        1017425@bugs.debian.org,
        =?iso-8859-1?Q?Martin-=C9ric?= Racine <martin-eric.racine@iki.fi>,
        stable@vger.kernel.org, regressions@lists.linux.dev,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Subject: Re: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN_BUFFER on
 CPUs that lack it
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References: <Yv7aRJ/SvVhSdnSB@decadent.org.uk>
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On Fri, Aug 19, 2022 at 02:33:08AM +0200, Ben Hutchings wrote:
> From: Ben Hutchings <benh@debian.org>
>=20
> The mitigation for PBRSB includes adding LFENCE instructions to the
> RSB filling sequence.  However, RSB filling is done on some older CPUs
> that don't support the LFENCE instruction.
>=20

Wait; what? There are chips that enable the RSB mitigations and DONT
have LFENCE ?!?