From patchwork Fri Apr 1 00:38:47 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefano Stabellini X-Patchwork-Id: 12797818 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 EA470C433FE for ; Fri, 1 Apr 2022 00:39:09 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.297161.506152 (Exim 4.92) (envelope-from ) id 1na5Jb-0000zD-Rx; Fri, 01 Apr 2022 00:38:59 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 297161.506152; Fri, 01 Apr 2022 00:38:59 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1na5Jb-0000wH-Ej; Fri, 01 Apr 2022 00:38:59 +0000 Received: by outflank-mailman (input) for mailman id 297161; Fri, 01 Apr 2022 00:38:56 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1na5JY-0007ot-KL for xen-devel@lists.xenproject.org; Fri, 01 Apr 2022 00:38:56 +0000 Received: from dfw.source.kernel.org (dfw.source.kernel.org [2604:1380:4641:c500::1]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 1c1ac557-b154-11ec-8fbc-03012f2f19d4; Fri, 01 Apr 2022 02:38:55 +0200 (CEST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9E1E3618B8; Fri, 1 Apr 2022 00:38:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF26EC340F2; Fri, 1 Apr 2022 00:38:53 +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: 1c1ac557-b154-11ec-8fbc-03012f2f19d4 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648773534; bh=SyJ8d/AZr5XFzu3v/AGdBw4+YWs6wkcRBAD8+aGiIR8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZNcF/aqp8YX0OngKR48lncjoj4oL3Gi2+JJHtCOdyA2QN/Kq7MCfGqZuJBFFR6EF7 7TxsX4uFnSgfelEtrkvyZVBSNITXikzOppt7A75SrAO1impSlpVT1bsDHAZpjKXHTd lJYpdwrWCrPdesQCZcou81J0K4uRZ7rIxcDO3IOF2BH6Ain5V79Ymfv6m40D+hKaIs DUrRdWD1HtmOjxOPfjqIgTIuxQ0I/9ZmjNum0jbdWitO8B4OMJ/BqgCkTE3jRdz5Gg 2tN0UieyjWC3vXnW3dLjYmekJaqBoVnwKKT/YbNjPLq4Rhfq9ioUX9sWd/8LWmunPw qSDQ4wMfiPlTg== From: Stefano Stabellini To: xen-devel@lists.xenproject.org Cc: sstabellini@kernel.org, jgross@suse.com, Bertrand.Marquis@arm.com, julien@xen.org, Volodymyr_Babchuk@epam.com, Stefano Stabellini Subject: [PATCH v4 9/9] docs: document dom0less + PV drivers Date: Thu, 31 Mar 2022 17:38:47 -0700 Message-Id: <20220401003847.38393-9-sstabellini@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 From: Stefano Stabellini Document how to use the feature and how the implementation works. Signed-off-by: Stefano Stabellini Reviewed-by: Luca Fancellu --- docs/features/dom0less.pandoc | 43 ++++++++++++++++++++++++++++++++--- 1 file changed, 40 insertions(+), 3 deletions(-) diff --git a/docs/features/dom0less.pandoc b/docs/features/dom0less.pandoc index c9edb529e1..725afa0558 100644 --- a/docs/features/dom0less.pandoc +++ b/docs/features/dom0less.pandoc @@ -90,6 +90,46 @@ Otherwise, they may be unusable in Xen (for instance if they are compressed). See docs/misc/arm/device-tree/booting.txt for more information. +PV Drivers +---------- + +It is possible to use PV drivers with dom0less guests with some +restrictions: + +- dom0less domUs that want to use PV drivers support should have the + "xen,enhanced" property set under their device tree nodes (see + docs/misc/arm/device-tree/booting.txt) +- a dom0 must be present (or another domain with enough privileges to + run the toolstack) +- after dom0 is booted, the utility "init-dom0less" must be run +- do not run "init-dom0less" while creating other guests with xl + +After the execution of init-dom0less, it is possible to use "xl" to +hotplug PV drivers to dom0less guests. E.g. xl network-attach domU. + +The implementation works as follows: +- Xen allocates the xenstore event channel for each dom0less domU that + has the "xen,enhanced" property, and sets HVM_PARAM_STORE_EVTCHN +- Xen does *not* allocate the xenstore page and sets HVM_PARAM_STORE_PFN + to ~0ULL (invalid) +- Dom0less domU kernels check that HVM_PARAM_STORE_PFN is set to invalid + - Old kernels will continue without xenstore support (Note: some old + buggy kernels might crash because they don't check the validity of + HVM_PARAM_STORE_PFN before using it! Disable "xen,enhanced" in + those cases) + - New kernels will wait for a notification on the xenstore event + channel (HVM_PARAM_STORE_EVTCHN) before continuing with the + initialization +- Once dom0 is booted, init-dom0less is executed: + - it allocates the xenstore shared page and sets HVM_PARAM_STORE_PFN + - it calls xs_introduce_domain +- Xenstored notices the new domain, initializes interfaces as usual, and + sends an event channel notification to the domain using the xenstore + event channel (HVM_PARAM_STORE_EVTCHN) +- The Linux domU kernel receives the event channel notification, checks + HVM_PARAM_STORE_PFN again and continue with the initialization + + Limitations ----------- @@ -107,9 +147,6 @@ limitations: information, the GIC version exposed to the domains started by Xen at boot is the same as the native GIC version. -- No PV drivers. There is no support for PV devices at the moment. All - devices need to be statically assigned to guests. - - Pinning vCPUs of domains started by Xen at boot can be done from the control domain, using `xl vcpu-pin` as usual. It is not currently possible to configure vCPU pinning without a control domain.