linux-kernel - Re: [RFC PATCH v3 1/2] x86: cpu/bugs: add AMD ERAPS support; hardware flushes RSB

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Message-ID: <0dd91e39-c4b7-4740-b469-6f71e48b72de@intel.com>
Date: Mon, 2 Dec 2024 10:25:57 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Amit Shah <amit@...nel.org>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, x86@...nel.org, linux-doc@...r.kernel.org
Cc: thomas.lendacky@....com, bp@...en8.de, tglx@...utronix.de,
 peterz@...radead.org, jpoimboe@...nel.org,
 pawan.kumar.gupta@...ux.intel.com, corbet@....net, mingo@...hat.com,
 dave.hansen@...ux.intel.com, hpa@...or.com, seanjc@...gle.com,
 pbonzini@...hat.com, daniel.sneddon@...ux.intel.com, kai.huang@...el.com,
 sandipan.das@....com, boris.ostrovsky@...cle.com, Babu.Moger@....com,
 david.kaplan@....com, dwmw@...zon.co.uk, andrew.cooper3@...rix.com,
 Amit Shah <Amit.Shah@....com>
Subject: Re: [RFC PATCH v3 1/2] x86: cpu/bugs: add AMD ERAPS support; hardware
 flushes RSB

On 12/2/24 10:09, Amit Shah wrote:
> I can still include the summary of the discussion in this patch - I
> just feel it isn't necessary with the rework.

It's necessary.

There's a new hardware feature. You want it to replace a software
sequence in certain situations. You have to make an actual, coherent
argument argument as to why the hardware feature is a suitable replacement.

For instance (and I'm pretty sure we've gone over this more than once),
the changelog here still makes the claim that a "context switch" and a
"mov-to-CR3" are the same thing.