linux-kernel - Re: [PATCH] x86/bugs: Qualify RETBLEED_INTEL

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Message-ID: <20251007221229.GAaOWQTadGWlZSeAo_@fat_crate.local>
Date: Wed, 8 Oct 2025 00:12:29 +0200
From: Borislav Petkov <bp@...en8.de>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: "Kaplan, David" <David.Kaplan@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>,
	Klaus Kusche <klaus.kusche@...puterix.info>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/bugs: Qualify RETBLEED_INTEL_MSG

On Tue, Oct 07, 2025 at 11:22:57AM -0700, Pawan Gupta wrote:
> Even when CPU mitigations are disabled there is still some handling
> required for mitigations like GDS that requires a write to MSR to ensure
> correct behavior.

When mitigations are compiled out there are no mitigations by definition. So
whatever you're talking about must be something else which should happen in
vendor code.

> IMO, rather than targeting the mitigation enabling code it might make more
> sense to compile out the actual mitigations scattered accross the kernel.
> This may also improve performance by reducing the code footprint, and can
> also help getting a cleaner disassembly.

Probably... however, it needs to be done smartly because sprinkling ifdeffery
and turning what is an already unreadable mess into a bigger abomination,
won't fly. Perhaps split out the mitigations glue into separate compilation
units and build-disable them... we'll see.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette