From patchwork Fri May 13 14:38:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Rahul Singh X-Patchwork-Id: 12848919 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id DD7FCC433EF for ; Fri, 13 May 2022 14:39:30 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.328548.551598 (Exim 4.92) (envelope-from ) id 1npWRp-00029s-5N; Fri, 13 May 2022 14:39:17 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 328548.551598; Fri, 13 May 2022 14:39:17 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1npWRp-00029l-29; Fri, 13 May 2022 14:39:17 +0000 Received: by outflank-mailman (input) for mailman id 328548; Fri, 13 May 2022 14:39:15 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1npWRn-00029d-UO for xen-devel@lists.xenproject.org; Fri, 13 May 2022 14:39:15 +0000 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by se1-gles-sth1.inumbo.com (Halon) with ESMTP id 755d8d63-d2ca-11ec-aa76-f101dd46aeb6; Fri, 13 May 2022 16:39:14 +0200 (CEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 23E88113E; Fri, 13 May 2022 07:39:13 -0700 (PDT) Received: from e109506.cambridge.arm.com (e109506.cambridge.arm.com [10.1.199.62]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D85F93F5A1; Fri, 13 May 2022 07:39:11 -0700 (PDT) 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: 755d8d63-d2ca-11ec-aa76-f101dd46aeb6 From: Rahul Singh To: xen-devel@lists.xenproject.org Cc: bertrand.marquis@arm.com, rahul.singh@arm.com, Andrew Cooper , George Dunlap , Jan Beulich , Julien Grall , Stefano Stabellini , Wei Liu Subject: [PATCH v3] xen/evtchn: Add design for static event channel signaling Date: Fri, 13 May 2022 15:38:57 +0100 Message-Id: X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 This patch introduces a new feature to support the signaling between two domains in dom0less system. Signed-off-by: Rahul Singh Reviewed-by: Stefano Stabellini --- v3 changes: - add dt node example for dom0 and domU. - add info about "xen,enhanced" property to enable the event-channel interface for domU guests. v2 changes: - switch to the one-subnode-per-evtchn under xen,domain" compatible node. - Add more detail about event-channel. --- docs/designs/dom0less-evtchn.md | 144 ++++++++++++++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 docs/designs/dom0less-evtchn.md diff --git a/docs/designs/dom0less-evtchn.md b/docs/designs/dom0less-evtchn.md new file mode 100644 index 0000000000..3c89a9fb7d --- /dev/null +++ b/docs/designs/dom0less-evtchn.md @@ -0,0 +1,144 @@ +# Signaling support between two domUs on dom0less system + +## Current state: Draft version + +## Proposer(s): Rahul Singh, Bertrand Marquis + +## Problem Statement: + +Dom0less guests would benefit from a statically-defined memory sharing and +signally system for communication. One that would be immediately available at +boot without any need for dynamic configurations. + +In embedded a great variety of guest operating system kernels exist, many of +which don't have support for xenstore, grant table, or other complex drivers. +Some of them are small kernel-space applications (often called "baremetal", +not to be confused with the term "baremetal" used in the data center which +means "without hypervisors") or RTOSes. Additionally, for safety reasons, users +often need to be able to configure the full system statically so that it can +be verified statically. + +Event channels are very simple and can be added even to baremetal applications. +This proposal introduces a way to define them statically to make them suitable +for dom0less embedded deployments. + +## Proposal: + +Event channels are the basic primitive provided by Xen for event notifications. +An event channel is a logical connection between 2 domains (more specifically +between dom1,port1, and dom2,port2). Each event has a pending and a masked bit. +The pending bit indicates the event has been raised. The masked bit is used by +the domain to prevent the delivery of that specific event. Xen only performs a +0 -> 1 transition on the pending bits and does not touch the mask bit. The +domain may toggle masked bits in the masked bit field and should clear the +pending bit when an event has been processed + +Events are received by a domain via an interrupt from Xen to the domain, +indicating when an event arrives (setting the bit). Further notifications are +blocked until the bit is cleared again. Events are delivered asynchronously to +a domain and are enqueued when the domain is not running. Xen supports two +different ABIs for event channel: FIFO and 2L. + +The event channel communication will be established statically between two +domains (dom0 and domU also) before unpausing the domains after domain creation. +Event channel connection information between domains will be passed to Xen via +the device tree node. The event channel will be created and established +in Xen before the domain started. The domain doesn’t need to do any operation +to establish a connection. Domain only needs hypercall +EVTCHNOP_send(local port) to send notifications to the remote guest. + +There is no need to describe the static event channel info in the domU device +tree. Static event channels are only useful in fully static configurations, +and in those configurations the domU device tree dynamically generated by Xen +is not needed. + +To enable the event-channel interface for domU guests include the +"xen,enhanced" property with an empty string ( or with the value +"enabled” or "evtchn") in domU Xen device tree node. + +Under the "xen,domain" compatible node, there need to be sub-nodes with +compatible "xen,evtchn" that describe the event channel connection between two +domains(dom0 and domU also). + +The event channel sub-node has the following properties: + +- compatible + + "xen,evtchn" + +- xen,evtchn + + The property is tuples of two numbers + (local-evtchn link-to-foreign-evtchn) where: + + local-evtchn is an integer value that will be used to allocate local port + for a domain to send and receive event notifications to/from the remote + domain. Maximum supported value is 2^17 for FIFO ABI and 4096 for 2L ABI. + + link-to-foreign-evtchn is a single phandle to a foreign evtchn to which + local-evtchn will be connected. + + +Example: + + chosen { + .... + + module@0 { + compatible = "multiboot,kernel", "multiboot,module"; + xen,uefi-binary = "..."; + bootargs = "..."; + + /* one sub-node per local event channel */ + ec1: evtchn@1 { + compatible = "xen,evtchn-v1"; + /* local-evtchn link-to-foreign-evtchn */ + xen,evtchn = <0xa &ec2>; + }; + }; + + domU1: domU1 { + compatible = "xen,domain"; + + /* one sub-node per local event channel */ + ec2: evtchn@2 { + compatible = "xen,evtchn-v1"; + /* local-evtchn link-to-foreign-evtchn */ + xen,evtchn = <0xa &ec1>; + }; + + ec3: evtchn@3 { + compatible = "xen,evtchn-v1"; + xen,evtchn = <0xb &ec5>; + }; + + ec4: evtchn@4 { + compatible = "xen,evtchn-v1"; + xen,evtchn = <0xc &ec6>; + }; + .... + }; + + domU2: domU2 { + compatible = "xen,domain"; + + /* one sub-node per local event channel */ + ec5: evtchn@5 { + compatible = "xen,evtchn-v1"; + /* local-evtchn link-to-foreign-evtchn */ + xen,evtchn = <0xa &ec3>; + }; + + ec6: evtchn@6 { + compatible = "xen,evtchn-v1"; + xen,evtchn = <0xb &ec4>; + }; + .... + }; + }; + +In above example three event channel comunications will be established: + + dom0 (port 0xa) <-----------------> domU1 (port 0xa) + domU1 (port 0xb) <-----------------> domU2 (port 0xa) + domU1 (port 0xc) <-----------------> domU2 (port 0xb)