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=-2.5 required=3.0 tests=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 53E88C433DF for ; Wed, 24 Jun 2020 12:52:26 +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 2E57620663 for ; Wed, 24 Jun 2020 12:52:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2E57620663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com 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 4.92) (envelope-from ) id 1jo4su-0001va-Ph; Wed, 24 Jun 2020 12:52:12 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jo4st-0001vS-JE for xen-devel@lists.xenproject.org; Wed, 24 Jun 2020 12:52:11 +0000 X-Inumbo-ID: 84a97c26-b619-11ea-bca7-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 84a97c26-b619-11ea-bca7-bc764e2007e4; Wed, 24 Jun 2020 12:52:10 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B1FE1ACED; Wed, 24 Jun 2020 12:52:09 +0000 (UTC) Subject: Re: [PATCH for-4.14] mm: fix public declaration of struct xen_mem_acquire_resource To: Julien Grall References: <20200623135246.66170-1-roger.pau@citrix.com> <044c278b-e0df-e389-b21a-66c7307997c4@suse.com> <20200623173150.GV735@Air-de-Roger> <3ea0ff91-8e5c-701c-ee31-4140b247f3c9@suse.com> <4651b23b-ca82-a478-debd-c20cdcd3facd@xen.org> <6195142d-6fa3-474d-3070-f43105742e79@xen.org> From: Jan Beulich Message-ID: <5193dc6d-0a4c-4e1b-d089-9ba359c19e3e@suse.com> Date: Wed, 24 Jun 2020 14:52:10 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <6195142d-6fa3-474d-3070-f43105742e79@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , paul@xen.org, Andrew Cooper , Ian Jackson , George Dunlap , xen-devel@lists.xenproject.org, =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 24.06.2020 14:47, Julien Grall wrote: > Hi, > > On 24/06/2020 13:08, Jan Beulich wrote: >> On 24.06.2020 12:52, Julien Grall wrote: >>> Hi Jan, >>> >>> On 24/06/2020 11:05, Jan Beulich wrote: >>>> On 23.06.2020 19:32, Roger Pau Monné wrote: >>>>> On Tue, Jun 23, 2020 at 05:04:53PM +0200, Jan Beulich wrote: >>>>>> On 23.06.2020 15:52, Roger Pau Monne wrote: >>>>>>> XENMEM_acquire_resource and it's related structure is currently inside >>>>>>> a __XEN__ or __XEN_TOOLS__ guarded section to limit it's scope to the >>>>>>> hypervisor or the toolstack only. This is wrong as the hypercall is >>>>>>> already being used by the Linux kernel at least, and as such needs to >>>>>>> be public. >>>>>> >>>>>> Actually - how does this work for the Linux kernel, seeing >>>>>> >>>>>> rc = rcu_lock_remote_domain_by_id(xmar.domid, &d); >>>>>> if ( rc ) >>>>>> return rc; >>>>>> >>>>>> rc = xsm_domain_resource_map(XSM_DM_PRIV, d); >>>>>> if ( rc ) >>>>>> goto out; >>>>>> >>>>>> in the function? >>>>> >>>>> It's my understanding (I haven't tried to use that hypercall yet on >>>>> FreeBSD, so I cannot say I've tested it), that xmar.domid is the >>>>> remote domain, which the functions locks and then uses >>>>> xsm_domain_resource_map to check whether the current domain has >>>>> permissions to do privileged operations against it. >>>> >>>> Yes, but that's a tool stack operation, not something the kernel >>>> would do all by itself. The kernel would only ever pass DOMID_SELF >>>> (or the actual local domain ID), I would think. >>> >>> You can't issue that hypercall directly from userspace because you need >>> to map the page in the physical address space of the toolstack domain. >>> >>> So the kernel has to act as the proxy for the hypercall. This is >>> implemented as mmap() in Linux. >> >> Oh, and there's no generic wrapping available here, unlike for >> dmop. > > It is not clear to me the sort of generic wrapping you are referring to. > Are you referring to a stable interface for an application? > >> Makes me wonder whether, for this purpose, there should >> be (have been) a new dmop with identical functionality, to >> allow such funneling. > > I am not sure how using DMOP will allow us to implement it fully in > userspace. Do you mind expanding it? dmop was designed so that a kernel proxying requests wouldn't need updating for every new request added to the interface. If the request here was made through a new dmop, the kernel would never have had a need to know of an interface structure that's of no interest to it, but only to the tool stack. Jan