linux-kernel - Re: [PATCH] x86/speculation: Mitigate eIBRS PBRSB predictions with WRMSR

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Message-ID: <Yz6PUJqThY9NPHRs@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Oct 2022 10:18:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Suraj Jitindar Singh <surajjs@...zon.com>, kvm@...r.kernel.org,
        sjitindarsingh@...il.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...e.de,
        dave.hansen@...ux.intel.com, seanjc@...gle.com,
        pbonzini@...hat.com, jpoimboe@...nel.org,
        daniel.sneddon@...ux.intel.com, pawan.kumar.gupta@...ux.intel.com,
        benh@...nel.crashing.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/speculation: Mitigate eIBRS PBRSB predictions with
 WRMSR

On Wed, Oct 05, 2022 at 04:46:12PM -0700, Jim Mattson wrote:

>                 rmb();

Since we're not doing memory ordering but speculation hardening, this is
completely the wrong way to spell LFENCE. Please use barrier_nospec() in
those cases.

And as has already been pointed out, there's one of those just two lines
down already.

Also, what Andrew said.