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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 9B19CC433B4 for ; Mon, 10 May 2021 15:56:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 73B70615FF for ; Mon, 10 May 2021 15:56:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231792AbhEJP52 (ORCPT ); Mon, 10 May 2021 11:57:28 -0400 Received: from mx2.suse.de ([195.135.220.15]:53580 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231953AbhEJP5N (ORCPT ); Mon, 10 May 2021 11:57:13 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1620662167; h=from:from:reply-to: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=cApuLUjoLlkqS05hp7WeKGa0gsDcjZToA7i927RlZ1w=; b=Ziq2h0OfHFlQLl5NEKSNYks7vSxpVAhSutHlpJhEVRe8bekZDu5+bvOQbnUtEdrhV41lia PqrTVq1MaH1VI7TkAapKoXb1199Gglqh2RkDqz+V4T7RPvNSF7NGQwMkJ4RPOWicYXn/QH O09j+bXNzKoy+rq+vn5dhoD2tZwlkVw= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 51A90B013; Mon, 10 May 2021 15:56:07 +0000 (UTC) Subject: Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL To: Andi Kleen , Borislav Petkov , Kuppuswamy Sathyanarayanan Cc: Peter Zijlstra , Andy Lutomirski , Dave Hansen , Dan Williams , Tony Luck , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org References: <4f8c9559dd04d8e8485c419c5ebc9471613f7928.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com> From: Juergen Gross Message-ID: <41463493-48bb-0e69-dcb2-3072e2ddf208@suse.com> Date: Mon, 10 May 2021 17:56:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="BqL4eMzTkoBzKW3U0nEwZbGI48AP58x2K" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --BqL4eMzTkoBzKW3U0nEwZbGI48AP58x2K Content-Type: multipart/mixed; boundary="FAVt0Lh0HaoOPaPwWOmPTVmjxqL2Rt4PR"; protected-headers="v1" From: Juergen Gross To: Andi Kleen , Borislav Petkov , Kuppuswamy Sathyanarayanan Cc: Peter Zijlstra , Andy Lutomirski , Dave Hansen , Dan Williams , Tony Luck , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org Message-ID: <41463493-48bb-0e69-dcb2-3072e2ddf208@suse.com> Subject: Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL References: <4f8c9559dd04d8e8485c419c5ebc9471613f7928.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com> In-Reply-To: --FAVt0Lh0HaoOPaPwWOmPTVmjxqL2Rt4PR Content-Type: multipart/mixed; boundary="------------0BB53C064B28DE2E43033EC9" Content-Language: en-US This is a multi-part message in MIME format. --------------0BB53C064B28DE2E43033EC9 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 10.05.21 17:52, Andi Kleen wrote: > \ >>>> CONFIG_PARAVIRT_XL will be used by TDX that needs couple of paravirt= >>>> calls that were hidden under CONFIG_PARAVIRT_XXL, but the rest of th= e >>>> config would be a bloat for TDX. >>> >>> Used how? Why is it bloat for TDX? >> >> Is there any major downside to move the halt related pvops functions >> from CONFIG_PARAVIRT_XXL to CONFIG_PARAVIRT? >=20 > I think the main motivation is to get rid of all the page table related= =20 > hooks for modern configurations. These are the bulk of the annotations = > and=C2=A0 cause bloat and worse code. Shadow page tables are really obs= cure=20 > these days and very few people still need them and it's totally=20 > reasonable to build even widely used distribution kernels without them.= =20 > On contrast most of the other hooks are comparatively few and also on=20 > comparatively slow paths, so don't really matter too much. >=20 > I think it would be ok to have a CONFIG_PARAVIRT that does not have pag= e=20 > table support, and a separate config option for those (that could be=20 > eventually deprecated). >=20 > But that would break existing .configs for those shadow stack users,=20 > that's why I think Kirill did it the other way around. No. We have PARAVIRT_XXL for Xen PV guests, and we have PARAVIRT for other hypervisor's guests, supporting basically the TLB flush operations and time related operations only. Adding the halt related operations to PARAVIRT wouldn't break anything. 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