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=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 003ADC433E6 for ; Tue, 26 Jan 2021 09:22:56 +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 8083D23104 for ; Tue, 26 Jan 2021 09:22:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8083D23104 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com 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.74677.134203 (Exim 4.92) (envelope-from ) id 1l4KYe-0005eU-7a; Tue, 26 Jan 2021 09:22:44 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 74677.134203; Tue, 26 Jan 2021 09:22:44 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4KYe-0005eN-4J; Tue, 26 Jan 2021 09:22:44 +0000 Received: by outflank-mailman (input) for mailman id 74677; Tue, 26 Jan 2021 09:22:42 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4KYc-0005eI-T4 for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 09:22:42 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id af954f1d-e2a4-4e54-bfe2-9bcb164a01cf; Tue, 26 Jan 2021 09:22:42 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 21EDFB28A; Tue, 26 Jan 2021 09:22:41 +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: af954f1d-e2a4-4e54-bfe2-9bcb164a01cf 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=1611652961; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2n908zCMUmsX5D88epOQn6BELj2i2fxn4jBnqXTdEDQ=; b=ErseDTWxPSXm3eQfjrnjUkJyZ1SOcMqixEuSfzgDZ0UxmlpkaeLUQIUr50tW79tdjAwAxT plJS9LjlBJYtsC99y8FzeWEdoKtgXQe7+d4Vt9argz5P2acl/7hMTP4Fnh2gLSLJt8+6TM EYAifTfkvvsigFOKmDPb6Adu3gzOT88= Subject: Re: [PATCH v4 1/2] xen: EXPERT clean-up and introduce UNSUPPORTED To: Stefano Stabellini Cc: Stefano Stabellini , andrew.cooper3@citrix.com, george.dunlap@citrix.com, iwj@xenproject.org, julien@xen.org, wl@xen.org, xen-devel@lists.xenproject.org References: <20210125212747.26676-1-sstabellini@kernel.org> From: Jan Beulich Message-ID: Date: Tue, 26 Jan 2021 10:22:41 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210125212747.26676-1-sstabellini@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 25.01.2021 22:27, Stefano Stabellini wrote: > A recent thread [1] has exposed a couple of issues with our current way > of handling EXPERT. > > 1) It is not obvious that "Configure standard Xen features (expert > users)" is actually the famous EXPERT we keep talking about on xen-devel > > 2) It is not obvious when we need to enable EXPERT to get a specific > feature > > In particular if you want to enable ACPI support so that you can boot > Xen on an ACPI platform, you have to enable EXPERT first. But searching > through the kconfig menu it is really not clear (type '/' and "ACPI"): > nothing in the description tells you that you need to enable EXPERT to > get the option. > > So this patch makes things easier by doing two things: > > - introduce a new kconfig option UNSUPPORTED which is clearly to enable > UNSUPPORTED features as defined by SUPPORT.md > > - change EXPERT options to UNSUPPORTED where it makes sense: keep > depending on EXPERT for features made for experts > > - tag unsupported features by adding (UNSUPPORTED) to the one-line > description > > - clarify the EXPERT one-line description > > [1] https://marc.info/?l=xen-devel&m=160333101228981 > > Signed-off-by: Stefano Stabellini Non-Arm bits Reviewed-by: Jan Beulich However, I have questions on the Arm ones (sorry for not noticing earlier, as I assume it was this way before already): > @@ -77,7 +77,7 @@ config SBSA_VUART_CONSOLE > SBSA Generic UART implements a subset of ARM PL011 UART. > > 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 Both of these default to y and have their _prompt_ conditional upon EXPERT. Which means only an expert can turn them _off_. Which doesn't make it look like these are unsupported? Or if anything, turning them off is unsupported? Jan