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 74AD6C43217 for ; Mon, 28 Nov 2022 22:40:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234372AbiK1Wk2 (ORCPT ); Mon, 28 Nov 2022 17:40:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41270 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233219AbiK1Wk0 (ORCPT ); Mon, 28 Nov 2022 17:40:26 -0500 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 307FD27B0E for ; Mon, 28 Nov 2022 14:40:25 -0800 (PST) Received: from zn.tnic (p5de8e9fe.dip0.t-ipconnect.de [93.232.233.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 646F81EC042F; Mon, 28 Nov 2022 23:40:23 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1669675223; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=lZmQ7j7zgK9JHgQnY7ydnqQbz44P4Bhdp+DPFB7I0JE=; b=JmX75N2bOGozIbq6a9mlp2lFnrW28dA6Bv62M/XaNO5nThh4xGC/EVb1FYs0RDQPA2dXpG mNTFLP+uVGAJLyMlCnqGzgeD3+qsXBcJSX2X6Wu2RSoDIcazWV9/lb6/xZ+MFrEdH0RjLw +ggtTzGAP56gM6H7IkB3AiLfjFKJgHo= Date: Mon, 28 Nov 2022 23:40:19 +0100 From: Borislav Petkov To: Pawan Gupta Cc: Breno Leitao , tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, jpoimboe@kernel.org, peterz@infradead.org, x86@kernel.org, cascardo@canonical.com, leit@meta.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] x86/bugs: Explicitly clear speculative MSR bits Message-ID: References: <20221124104650.533427-1-leitao@debian.org> <20221128220358.n5vk6youcdl2er35@desk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221128220358.n5vk6youcdl2er35@desk> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 28, 2022 at 02:03:58PM -0800, Pawan Gupta wrote: > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 3e3230cccaa7..cfc2ed2661fc 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -66,7 +66,7 @@ static DEFINE_MUTEX(spec_ctrl_mutex); > */ > void write_spec_ctrl_current(u64 val, bool force) > { > - if (this_cpu_read(x86_spec_ctrl_current) == val) > + if (!force && this_cpu_read(x86_spec_ctrl_current) == val) > return; > this_cpu_write(x86_spec_ctrl_current, val); Still looks hacky to me. I think it would be a lot cleaner if MSR_IA32_SPEC_CTRL gets cleaned of the speculation bits in init_speculation_control() which gets run on *every* CPU. So by the time check_bugs() gets to setup stuff, the MSR will be ready to go regardless. I.e., something like this (not supposed to work - just to show what I mean): diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 73cc546e024d..367732c92942 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -993,9 +993,19 @@ static void init_speculation_control(struct cpuinfo_x86 *c) * Intel CPUs, for finer-grained selection of what's available. */ if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) { + u64 msr; + set_cpu_cap(c, X86_FEATURE_IBRS); set_cpu_cap(c, X86_FEATURE_IBPB); set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL); + + /* + * Clear speculation control settings from a previous kernel + * run, i.e., kexec. + */ + rdmsrl(MSR_IA32_SPEC_CTRL, msr); + if (msr & SPEC_CTRL_MASK) + wrmsr (MSR_IA32_SPEC_CTRL, msr & ~SPEC_CTRL_MASK); } if (cpu_has(c, X86_FEATURE_INTEL_STIBP)) -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette