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 X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97ED7C433DF for ; Tue, 26 May 2020 09:19:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 54F1C2073B for ; Tue, 26 May 2020 09:19:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="iKa2bVBp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731719AbgEZJTR (ORCPT ); Tue, 26 May 2020 05:19:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54878 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731600AbgEZJTR (ORCPT ); Tue, 26 May 2020 05:19:17 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 11CD7C03E97E; Tue, 26 May 2020 02:19:17 -0700 (PDT) Received: from zn.tnic (p200300ec2f0f91004890e1585abde4e7.dip0.t-ipconnect.de [IPv6:2003:ec:2f0f:9100:4890:e158:5abd:e4e7]) (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 E9AF21EC01CE; Tue, 26 May 2020 11:19:13 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1590484754; 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=3q+7t7sjlYH1ceIvNrmNgbY6YY9E6lQweSEw445KMuQ=; b=iKa2bVBpMQp6StjjDbQaxUSuJ6wTp1s+D5je8Zka3UYOO595HcNgIRtDL9u0hOFnuPhGDR MQnn6PnjduoWek/zB3TtJ35+Q0grOSS/8KmKwPz0q9/upZHz5W9p3CmZZPhGuWcO6Wb/Nn Y120KdDXjix8h/C8LNwg7L1XZb/LHKU= Date: Tue, 26 May 2020 11:19:09 +0200 From: Borislav Petkov To: Sean Christopherson Cc: Joerg Roedel , x86@kernel.org, hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Thomas Hellstrom , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Joerg Roedel , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v3 64/75] x86/sev-es: Cache CPUID results for improved performance Message-ID: <20200526091909.GB28228@zn.tnic> References: <20200428151725.31091-1-joro@8bytes.org> <20200428151725.31091-65-joro@8bytes.org> <20200520051637.GA16599@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200520051637.GA16599@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 19, 2020 at 10:16:37PM -0700, Sean Christopherson wrote: > The whole cache on-demand approach seems like overkill. The number of CPUID > leaves that are invoked after boot with any regularity can probably be counted > on one hand. IIRC glibc invokes CPUID to gather TLB/cache info, XCR0-based > features, and one or two other leafs. A statically sized global array that's > arbitrarily index a la x86_capability would be just as simple and more > performant. It would also allow fancier things like emulating CPUID 0xD in > the guest if you want to go down that road. And before we do any of that "caching" or whatnot, I'd like to see numbers justifying its existence. Because if it is only a couple of CPUID invocations and the boot delay is immeasurable, then it's not worth the effort. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette