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 AAA81C6FA86 for ; Mon, 26 Sep 2022 14:48:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235306AbiIZOsM (ORCPT ); Mon, 26 Sep 2022 10:48:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50472 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234674AbiIZOrs (ORCPT ); Mon, 26 Sep 2022 10:47:48 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C05F6B1D4; Mon, 26 Sep 2022 06:12:42 -0700 (PDT) Received: from zn.tnic (p200300ea9733e74d329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:9733:e74d:329c:23ff:fea6:a903]) (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 ED5171EC051E; Mon, 26 Sep 2022 15:12:35 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1664197956; 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=WoAsNIjxtOydRj3E9e8AKmT+MPVf0jUVuDQQzfJocNg=; b=YlkrwAcwyMQjQRO0wTBEUyoDvIIogt7PwJBqH9c6yVxgqYlhBY5xt3oHREab1EXAgd1+Jt ajd5Z6pFsRNvdhCy0jlBQv3Pytt9U52OucBWsQsAJGfx18Xvd1FQyx1QD2bygaB9ytBcb2 ccjY1VjlLyZmDeDfFXjwOze/QNV1TC0= Date: Mon, 26 Sep 2022 15:12:32 +0200 From: Borislav Petkov To: Maxim Levitsky Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Pawan Gupta , Ingo Molnar , Josh Poimboeuf , Namhyung Kim , Tony Luck , Paolo Bonzini , "H. Peter Anvin" , Arnaldo Carvalho de Melo , Thomas Gleixner , Alexander Shishkin , Tim Chen , "David S. Miller" , Dave Hansen , "Chang S. Bae" , Jane Malalane , Kees Cook , Kan Liang , Peter Zijlstra , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Herbert Xu , Jiri Olsa , Mark Rutland , linux-perf-users@vger.kernel.org, "open list:CRYPTO API" Subject: Re: [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap instead of clear_cpu_cap Message-ID: References: <20220718141123.136106-1-mlevitsk@redhat.com> <20220718141123.136106-2-mlevitsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Tue, Sep 20, 2022 at 11:20:47AM +0300, Maxim Levitsky wrote: > If I understand that correctly, the difference between clear_cpu_cap and setup_clear_cpu_cap > is that setup_clear_cpu_cap should be called early when only the boot cpu is running and it > > 1. works on 'boot_cpu_data' which represents the boot cpu. > 2. sets a bit in 'cpu_caps_cleared' which are later applied to all CPUs, including these that are hotplugged. Yes. > On the other hand the clear_cpu_cap just affects the given 'struct cpuinfo_x86'. Yes. > Call of 'clear_cpu_cap(&boot_cpu_data, X86_FEATURE_ARCH_LBR)' is weird since it still affects 'boot_cpu_data' > but doesn't affect 'cpu_caps_cleared' Yes. > I assumed that this was a mistake and the intention was to disable the feature on all CPUs. peterz says yes. > I need this patch because in the next patch, I change the clear_cpu_cap such as it detects being > called on boot_cpu_data and in this case also clears bits in 'cpu_caps_cleared', thus > while this patch does introduce a functional change, the next patch doesn't since this is the only > place where clear_cpu_cap is called explicitly on 'boot_cpu_data' This is not needed - this patch doing setup_clear_cpu_cap() should suffice. But, there must be something you're fixing with this. Which is it? Some weird virt config? > I do now notice that initcalls are run after smp is initialized, which > means that this code doesn't really disable the CPUID feature on all > CPUs at all. Well, not exactly. There's do_pre_smp_calls() which is where the early_initcall() thing is run. So setup_clear_cpu_cap() will make sure that the feature bit is cleared when the APs come online. Do you have a virt configuration where you can test this case where the feature flag is clear on all CPUs when it fails? I.e., "arch_lbr" will disappear in /proc/cpuinfo completely. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette