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Peter Anvin" , Klaus Kusche , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] x86/bugs: Qualify RETBLEED_INTEL_MSG Message-ID: <20251102200902.GDaQe6Xo0plI8glTbE@fat_crate.local> References: <20251007182257.ywrqrrhgrtrviila@desk> <20251007221229.GAaOWQTadGWlZSeAo_@fat_crate.local> <20251007230821.5shpa3pusyzaohb2@desk> <20251008102136.GAaOY7MBd4_VBPBNtG@fat_crate.local> <20251009101557.GAaOeLXYDjOnyFTWdg@fat_crate.local> <20251009171331.vplg2zcfystojcxo@desk> <20251009231437.GCaOhB3aeJlTCu_OkQ@fat_crate.local> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20251009231437.GCaOhB3aeJlTCu_OkQ@fat_crate.local> On Fri, Oct 10, 2025 at 01:14:37AM +0200, Borislav Petkov wrote: > On Thu, Oct 09, 2025 at 06:13:20PM +0000, Kaplan, David wrote: > > If we really want to optimize a CONFIG_CPU_MITIGATIONS=n kernel, why not > > also look at alternatives that will never be enabled? > > > > All the extra NOPs I think can affect performance in various ways and if > > there was a way at compile time to know that the alternative would never be > > enabled (because the feature is completely dependent on a cpu mitigation) > > you could eliminate the NOPs... > > I don't see why not. That mitigations gunk should be just like any other > CONFIG_-controllable item and not simply "leak" into the build because, oh > well, we've done it this way from the very beginning and no one should touch > it. > > So yeah, eventually we should try this. I've been experimenting with > untangling bugs.c today, will check how much it actually saves us when > I finish beating the stinking pile into submission. So I can't say that it is insignificant: text data bss dec hex filename 30787172 11613226 7863812 50264210 2fef892 vmlinux.with 30210273 11598338 6061260 47869871 2da6faf vmlinux.without that's ~500K code on my tailored config, meaning I haven't even enabled all mitigations. So I'm thinking we should do this, but slowly, piecemeal, until we have settled on the layout. I'll send some patches soon to gather opinions... Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette