From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 257A6C001B0 for ; Fri, 11 Aug 2023 09:39:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231127AbjHKJjd (ORCPT ); Fri, 11 Aug 2023 05:39:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51164 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235301AbjHKJjT (ORCPT ); Fri, 11 Aug 2023 05:39:19 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79A5A3C39 for ; Fri, 11 Aug 2023 02:38:55 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1691746732; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lKW6frnZPBO5k+LotvM4JpLFikbfsSCjaOX4sVGJgnk=; b=D0i22V92/L27VI+3UVhXvKn0jDvqnaJWZifCYe+RlNIYzydr5vMn8ePrh3o3Ac344yiA4w 20NfmtAPP7o9PjlhcsSKCVzqWwTk8pzRLw6DneSMFiSBLs9EXbsXTyhXpTiMJZLCKX6zBW bqF3AphRjuSSgvH4bnGY+y/0oo0bAEl/JYUm0jDdxiScHEGm3jvYd80ut13EcWXgoPVCcc p9NxetnS73Jd44PZDpOVz8Ldtk9mzSNUe7TkjVzFWjrHP4KSOzymGJzN8QsEN2LcNEK04C q/a3Oxh5n5QV77Hy+6kwN9KIS3feJk51rEXRhcOXHd3bQVUFZY/sOWTpC6x7RQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1691746732; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lKW6frnZPBO5k+LotvM4JpLFikbfsSCjaOX4sVGJgnk=; b=qagwCRX5cScfEeJVaZgCvgosUZxBoeq9Sr/GBvs7mgCBCjE+HKTU0A3X6D1cGfbAOsYucv fNSRuSI4MNLCCHAw== To: Peter Zijlstra Cc: LKML , x86@kernel.org, Borislav Petkov , Ashok Raj , Arjan van de Ven Subject: Re: [patch 29/30] x86/microcode: Prepare for minimal revision check In-Reply-To: <20230810205427.GG212435@hirez.programming.kicks-ass.net> References: <20230810153317.850017756@linutronix.de> <20230810160806.617422055@linutronix.de> <20230810205427.GG212435@hirez.programming.kicks-ass.net> Date: Fri, 11 Aug 2023 11:38:51 +0200 Message-ID: <871qg9j4us.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 10 2023 at 22:54, Peter Zijlstra wrote: > On Thu, Aug 10, 2023 at 08:38:09PM +0200, Thomas Gleixner wrote: >> From: Thomas Gleixner >> >> Applying microcode late can be fatal for the running kernel when the update >> changes functionality which is in use already in a non-compatible way, >> e.g. by removing a CPUID bit. > > This includes all compatibility constraints? Because IIRC we've also had > trouble because a CPUID bit got set. Kernel didn't know about, didn't > manage it, but userspace saw the bit and happily tried to use it. We don't know. If the microcoders screw that minrev constraint up, then we are up the creek w/o a paddle as before. > Ofc I can't remember the exact case :/ but anything that changes the > xsave size/state would obviously cause trouble. Details. :)