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=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 430A5C433DB for ; Tue, 26 Jan 2021 18:26:44 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DFE1B207A9 for ; Tue, 26 Jan 2021 18:26:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFE1B207A9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.75404.135767 (Exim 4.92) (envelope-from ) id 1l4T2h-0000hA-Qh; Tue, 26 Jan 2021 18:26:19 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 75404.135767; Tue, 26 Jan 2021 18:26:19 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4T2h-0000h3-NR; Tue, 26 Jan 2021 18:26:19 +0000 Received: by outflank-mailman (input) for mailman id 75404; Tue, 26 Jan 2021 18:26:19 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4T2h-0000gy-24 for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 18:26:19 +0000 Received: from mail.kernel.org (unknown [198.145.29.99]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 1175d09d-db78-45e6-b647-de1be20cd0f9; Tue, 26 Jan 2021 18:26:18 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 2FB62207BC; Tue, 26 Jan 2021 18:26:17 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 1175d09d-db78-45e6-b647-de1be20cd0f9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611685577; bh=abtO3RAm6Hn7mmYf4RLA+aTAQjRjKGymTLDaAGREULU=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=dGyXl338IAFFwwBZtOQ/MGkFvbAN4zLo6Pj59FcxtDALiRPf0/3eOvAYC1cS1/ggM xx0ESbHP8sTyMkq2Ets2qM3fhsWcqz83JXi2ACaWdxdiNKaHkkvZyGLUvgMXUm7/5Y cNiiqKZsXcK4YD0Pdybk7mkriknjpCYeZLNC959PzczKLfscEbTd9bkjoC70rkeTsK JQuthb70478+FeBnq3MiNpCmrVCKQK3HAJtmtjlvpRi63zI2GdnQweL8pu2Z8BCujs BWPjxgv9XTL4A7yjKZC4JbpaA8RH+i9mlyGCb4TiJ9Yo4IUQThtSigy4oNGMBK2y9P EBoUtOcivHTKA== Date: Tue, 26 Jan 2021 10:26:16 -0800 (PST) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Julien Grall cc: Stefano Stabellini , xen-devel@lists.xenproject.org, Stefano Stabellini , andrew.cooper3@citrix.com, george.dunlap@citrix.com, iwj@xenproject.org, jbeulich@suse.com, wl@xen.org Subject: Re: [PATCH v4 1/2] xen: EXPERT clean-up and introduce UNSUPPORTED In-Reply-To: <616b0552-33fc-360e-664c-44178e5afc6a@xen.org> Message-ID: References: <20210125212747.26676-1-sstabellini@kernel.org> <616b0552-33fc-360e-664c-44178e5afc6a@xen.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Tue, 26 Jan 2021, Julien Grall wrote: > Hi Stefano, > > On 25/01/2021 21:27, Stefano Stabellini wrote: > > config ARM_SSBD > > - bool "Speculative Store Bypass Disable" if EXPERT > > + bool "Speculative Store Bypass Disable (UNSUPPORTED)" if UNSUPPORTED > > depends on HAS_ALTERNATIVE > > default y > > help > > @@ -87,7 +87,7 @@ config ARM_SSBD > > If unsure, say Y. > > config HARDEN_BRANCH_PREDICTOR > > - bool "Harden the branch predictor against aliasing attacks" if EXPERT > > + bool "Harden the branch predictor against aliasing attacks > > (UNSUPPORTED)" if UNSUPPORTED > > default y > > help > > Speculation attacks against some high-performance processors rely on > > I read through the back and forth between Bertrand and Jan about > "UNSUPPORTED". However, I still don't understand why those two options are > moved to UNSUPPORTED. > > Both options will only build the code to enable the mitigation. The decision > is still based on the processor you are running on. > > In addition to that, ARM_SSBD can also be forced enabled/disabled on the > command line. Yes, you are right. HARDEN_BRANCH_PREDICTOR and ARM_SSBD should remain EXPERT as they are today. It was a mistake to change them to UNSUPPORTED. > A user may want to compile out the code if the target processor is not the > affected by the two issues. This wouldn't be much different to Xen deciding to > not enabling the mitigation. > > I would view the two options as supported but not security supported. So this > seems to fit exactly in the definition of EXPERT rather than UNSUPPORTED. Yes, I'll leave them unmodified.