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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 65BFAC54FCC for ; Tue, 21 Apr 2020 18:45:28 +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 37A372068F for ; Tue, 21 Apr 2020 18:45:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=xen.org header.i=@xen.org header.b="LoMkH8FF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37A372068F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jQxtF-0004Z4-K7; Tue, 21 Apr 2020 18:45:01 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jQxtE-0004Yz-8F for xen-devel@lists.xenproject.org; Tue, 21 Apr 2020 18:45:00 +0000 X-Inumbo-ID: 33f6a560-8400-11ea-83d8-bc764e2007e4 Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 33f6a560-8400-11ea-83d8-bc764e2007e4; Tue, 21 Apr 2020 18:44:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=3LRpHjK56BbXSmp/E5Wp5stHCUvVNHhkgn/mMIlOrhM=; b=LoMkH8FFHvgYsF++CozfveQZeI t4Op3K1otGTctTHTuU3zl74R8X/TI42NDaGJFKWBijnPsJ3bjC0tVl1+plJ7sNZ8SRNt7J8vGhfWg emAFgx4MSrmfb5cboJ2uM5R0LdaEUnaJDH906q+4rA15sTbSVy/+fOYSxSSnfWXXO8Rg=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jQxtB-0006q3-SR; Tue, 21 Apr 2020 18:44:57 +0000 Received: from [54.239.6.185] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1jQxtB-0001cU-Lp; Tue, 21 Apr 2020 18:44:57 +0000 Subject: Re: [PATCH v2 4/4] x86: adjustments to guest handle treatment To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Jan Beulich References: <9d4b738a-4487-6bfc-3076-597d074c7b47@suse.com> <20200421173010.GY28601@Air-de-Roger> From: Julien Grall Message-ID: <524885c7-5189-7215-41e6-1652a8bd08a2@xen.org> Date: Tue, 21 Apr 2020 19:44:55 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200421173010.GY28601@Air-de-Roger> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Andrew Cooper , Tim Deegan , George Dunlap , "xen-devel@lists.xenproject.org" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi, On 21/04/2020 18:30, Roger Pau Monné wrote: > On Tue, Apr 21, 2020 at 11:13:23AM +0200, Jan Beulich wrote: >> First of all avoid excessive conversions. copy_{from,to}_guest(), for >> example, work fine with all of XEN_GUEST_HANDLE{,_64,_PARAM}(). > > I'm not sure I understand the difference between those two, as they > are both placeholders for linear guest addresses? > > AFAICT XEN_GUEST_HANDLE should be used for guest pointers inside of an > hypercall struct, while XEN_GUEST_HANDLE_PARAM is for guest pointers > as hypercall arguments. But those are both just guest pointers, > whether they are a parameter to the hypercall or a field in a > struct, and hence could use the same type? > > I assume there's some reason for not doing so, and I see the comment > about other arches, but again a linear guest address is just that in > all arches, regardless of it's placement. On Arm: * XEN_GUEST_HANDLE() will always be 64-bit on both 32-bit and 64-bit hypervisor. * XEN_GUEST_HANDLE_PARAM() will be 32-bit for 32-bit hypervisor. For 64-bit hypervisor, it will be 64-bit. Per the ABI, each argument only fit a register. So you could not use XEN_GUEST_HANDLE() as now an argument will be held in 2 registers on 32-bit. We also want the structure layout to be the same for 32-bit and 64-bit. So using XEN_GUEST_HANDLE_PARAM() everywhere is not the solution as the virtual address is not the same. We could possibly convert internally XEN_GUEST_HANDLE_PARAM() to XEN_GUEST_HANDLE(), but I am not sure how this would be beneficial. We would have to use 2 registers for arm 32-bit everytime. Cheers, -- Julien Grall