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,URIBL_BLOCKED,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 6A950C433DF for ; Wed, 24 Jun 2020 13:07:45 +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 3BD1120706 for ; Wed, 24 Jun 2020 13:07:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3BD1120706 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 1jo57c-0003OB-TH; Wed, 24 Jun 2020 13:07:24 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jo57b-0003O6-PD for xen-devel@lists.xenproject.org; Wed, 24 Jun 2020 13:07:23 +0000 X-Inumbo-ID: a451ba14-b61b-11ea-8496-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id a451ba14-b61b-11ea-8496-bc764e2007e4; Wed, 24 Jun 2020 13:07:23 +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 CAA42AEFE; Wed, 24 Jun 2020 13:07:21 +0000 (UTC) Subject: Re: [PATCH for-4.14] mm: fix public declaration of struct xen_mem_acquire_resource To: paul@xen.org 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> <5193dc6d-0a4c-4e1b-d089-9ba359c19e3e@suse.com> <000b01d64a26$7aacb580$70062080$@xen.org> From: Jan Beulich Message-ID: <2bcda30f-fa95-adea-d19a-4d9a4c00d130@suse.com> Date: Wed, 24 Jun 2020 15:07:14 +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: <000b01d64a26$7aacb580$70062080$@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' , 'Julien Grall' , 'Wei Liu' , 'Andrew Cooper' , 'Ian Jackson' , 'George Dunlap' , xen-devel@lists.xenproject.org, =?UTF-8?B?J1JvZ2VyIFBhdSBNb25uw6kn?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 24.06.2020 14:53, Paul Durrant wrote: >> -----Original Message----- >> From: Jan Beulich >> Sent: 24 June 2020 13:52 >> To: Julien Grall >> Cc: Roger Pau Monné ; xen-devel@lists.xenproject.org; paul@xen.org; Andrew >> Cooper ; George Dunlap ; Ian Jackson >> ; Stefano Stabellini ; Wei Liu >> Subject: Re: [PATCH for-4.14] mm: fix public declaration of struct xen_mem_acquire_resource >> >> 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. > > How would the pages get mapped into process address space if the > kernel doesn't know what's being done? Urgh, yes, silly me. Jan