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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 8C006C433B4 for ; Wed, 14 Apr 2021 08:47:41 +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 37C42610E8 for ; Wed, 14 Apr 2021 08:47:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37C42610E8 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.110369.210658 (Exim 4.92) (envelope-from ) id 1lWbB5-00062g-GK; Wed, 14 Apr 2021 08:47:15 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 110369.210658; Wed, 14 Apr 2021 08:47:15 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lWbB5-00062Z-D4; Wed, 14 Apr 2021 08:47:15 +0000 Received: by outflank-mailman (input) for mailman id 110369; Wed, 14 Apr 2021 08:47:15 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lWbB4-00062U-VZ for xen-devel@lists.xenproject.org; Wed, 14 Apr 2021 08:47:15 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id e4018436-0f9e-4935-ae33-8813a53348ec; Wed, 14 Apr 2021 08:47:13 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0A371ACC4; Wed, 14 Apr 2021 08:47:13 +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: e4018436-0f9e-4935-ae33-8813a53348ec 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=1618390033; 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=D4lEBVogTgQ1ZXXAYsO22rt4q6Shor33gD5YfZD62g4=; b=tdMnNQVkMbfZrfcNG65NCHpqwtNw5vmB2h4n05/8aSs6tqQyu9iAFzCJrYZzfqI6/8+ch8 AXDJGnBZei3BT26URNaWHTBqqFXWMwrCtC4lDdhm89y0S/eT3Yro25oP1A1xD2Ph9pyFhC UNaBhT6v/83oESzocFnnEZ7RCpvL564= Subject: Re: [PATCH v2] xen/pci: Refactor PCI MSI interrupts related code To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: Julien Grall , xen-devel@lists.xenproject.org, bertrand.marquis@arm.com, Andrew Cooper , Wei Liu , George Dunlap , Ian Jackson , Stefano Stabellini , Paul Durrant , Volodymyr Babchuk , Daniel De Graaf , Rahul Singh References: From: Jan Beulich Message-ID: <026a9a34-b010-39eb-ad2c-e404f69cb4d4@suse.com> Date: Wed, 14 Apr 2021 10:47:12 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 14.04.2021 10:28, Roger Pau Monné wrote: > On Wed, Apr 14, 2021 at 09:08:53AM +0200, Jan Beulich wrote: >> On 13.04.2021 19:12, Julien Grall wrote: >>> On 12/04/2021 11:49, Roger Pau Monné wrote: >>>> On Fri, Apr 09, 2021 at 05:00:41PM +0100, Rahul Singh wrote: >>>>> --- a/xen/include/xen/vpci.h >>>>> +++ b/xen/include/xen/vpci.h >>>>> @@ -91,6 +91,7 @@ struct vpci { >>>>> /* FIXME: currently there's no support for SR-IOV. */ >>>>> } header; >>>>> >>>>> +#ifdef CONFIG_PCI_MSI_INTERCEPT >>>>> /* MSI data. */ >>>>> struct vpci_msi { >>>>> /* Address. */ >>>>> @@ -136,6 +137,7 @@ struct vpci { >>>>> struct vpci_arch_msix_entry arch; >>>>> } entries[]; >>>>> } *msix; >>>>> +#endif /* CONFIG_PCI_MSI_INTERCEPT */ >>>> >>>> Note that here you just remove two pointers from the struct, not that >>>> I'm opposed to it, but it's not that much space that's saved anyway. >>>> Ie: it might also be fine to just leave them as NULL unconditionally >>>> on Arm. >>> >>> Can the two pointers be NULL on x86? If not, then I would prefer if they >>> disappear on Arm so there is less chance to make any mistake (such as >>> unconditionally accessing the pointer in common code). >> >> Alternative proposal: How about making it effectively impossible to >> de-reference the pointer on Arm by leaving the field there, but having >> the struct definition available on non-Arm only? > > We could place the struct definitions somewhere else protected by > CONFIG_PCI_MSI_INTERCEPT, but I'm not sure that would be much > different than the current proposal, and overall I think I prefer this > approach then, as we keep the definition and the usage closer > together. > > Maybe we could slightly modify the current layout so that > the field is always present, but the struct definition is made > conditional to CONFIG_PCI_MSI_INTERCEPT? You mean like this /* MSI data. */ struct vpci_msi { #ifdef CONFIG_PCI_MSI_INTERCEPT /* Address. */ ... struct vpci_arch_msix_entry arch; } entries[]; #endif /* CONFIG_PCI_MSI_INTERCEPT */ } *msix; ? I could live with it, but this would have the compiler not refuse e.g. sizeof(struct vpci_msi) or instantiation of the struct as a (local) variable, unlike my proposal. Jan