linux-kernel - Re: [PATCH v10 03/15] x86/alternatives: Disable LASS when patching kernel alternatives

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Message-ID: <20251022102253.GW3419281@noisy.programming.kicks-ass.net>
Date: Wed, 22 Oct 2025 12:22:53 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Jonathan Corbet <corbet@....net>,
	"H . Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	"Kirill A . Shutemov" <kas@...nel.org>, Xin Li <xin@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Sean Christopherson <seanjc@...gle.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Laight <david.laight.linux@...il.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH v10 03/15] x86/alternatives: Disable LASS when patching
 kernel alternatives

On Wed, Oct 22, 2025 at 11:40:19AM +0200, Borislav Petkov wrote:

> > But that's not the same, stac() and clac() are FEATURE_SMAP, these are
> > FEATURE_LASS.
> 
> So?

That's confusing. Just keep them separate alternatives.

> Are you thinking of toggling features and then something else getting disabled
> in the process?

I'm thinking that machines without LASS don't need the clac/stac in
these places. And when reading the asm, the FEATURE_LASS is a clue.