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 B1522C433FE for ; Mon, 21 Nov 2022 15:53:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229852AbiKUPxR (ORCPT ); Mon, 21 Nov 2022 10:53:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229585AbiKUPxL (ORCPT ); Mon, 21 Nov 2022 10:53:11 -0500 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19FD2CB68D; Mon, 21 Nov 2022 07:53:10 -0800 (PST) Received: from zn.tnic (p200300ea9733e725329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:9733:e725:329c: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 9D4D41EC02FE; Mon, 21 Nov 2022 16:53:08 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1669045988; 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=ovoD+OFlGzUpGbbTqt/UdHTpTxjHta09GD2GLSLjtCA=; b=VSBDoJ5NcTC1m5fgrXm9tbg3XMvDOsrw3RQFtSvrB8an+Fz5HXdvj0Tuc5ep2k2HccQGyy 8WvXk3s0PeQTTR3XBGBOfa+pMXlj+f6HmOACwnsgsXVGWdNAmRkrNbcGcZshDam+MkutHR wwLl8QWtcBaPFbWNKXcAVovqerKVr8k= Date: Mon, 21 Nov 2022 16:53:04 +0100 From: Borislav Petkov To: Sean Christopherson Cc: Dave Hansen , Jiaxi Chen , kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, pbonzini@redhat.com, ndesaulniers@google.com, alexandre.belloni@bootlin.com, peterz@infradead.org, jpoimboe@kernel.org, chang.seok.bae@intel.com, pawan.kumar.gupta@linux.intel.com, babu.moger@amd.com, jmattson@google.com, sandipan.das@amd.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, fenghua.yu@intel.com, keescook@chromium.org, nathan@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/6] x86: KVM: Advertise CMPccXADD CPUID to user space Message-ID: References: <20221118141509.489359-1-jiaxi.chen@linux.intel.com> <20221118141509.489359-2-jiaxi.chen@linux.intel.com> <6d7fae50-ef3c-dc1e-336c-691095007117@intel.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-kernel@vger.kernel.org On Mon, Nov 21, 2022 at 03:48:06PM +0000, Sean Christopherson wrote: > Actually, for these features that don't require additional KVM enabling, KVM isn't > making the feature avaiable to the guest. KVM is just advertising to userspace > that KVM "supports" these features. Userspace ultimately controls guest CPUID; > outside of a few special cases, KVM neither rejects nor filters unsupported bits > in CPUID. So is there any point to those "enable it in KVM" patches streaming constantly? AFAICT, the only reason is to "pass through" the CPUID bit to the guest in case KVM is not showing it in the intercepted CPUID... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette