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=-2.3 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 DC2FFC76196 for ; Mon, 15 Jul 2019 13:49:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 B90662081C for ; Mon, 15 Jul 2019 13:49:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B90662081C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38858 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hn1M5-0004Eq-Oc for qemu-devel@archiver.kernel.org; Mon, 15 Jul 2019 09:49:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53235) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hn1Lh-0002zq-5Z for qemu-devel@nongnu.org; Mon, 15 Jul 2019 09:49:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hn1Lg-0001kd-0i for qemu-devel@nongnu.org; Mon, 15 Jul 2019 09:49:01 -0400 Received: from foss.arm.com ([217.140.110.172]:48182) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hn1Ld-0001e9-JY; Mon, 15 Jul 2019 09:48:57 -0400 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 6DBAA28; Mon, 15 Jul 2019 06:48:52 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 697233F71F; Mon, 15 Jul 2019 06:48:51 -0700 (PDT) Date: Mon, 15 Jul 2019 14:48:49 +0100 From: Mark Rutland To: Dave Martin Message-ID: <20190715134848.GI56232@lakrids.cambridge.arm.com> References: <1b0aa6b2-80b1-a72e-6849-7323c3b9c6bc@huawei.com> <20190715134059.GJ2790@e103592.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190715134059.GJ2790@e103592.cambridge.arm.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 217.140.110.172 Subject: Re: [Qemu-devel] [RFC] Add virtual SDEI support in qemu X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marc Zyngier , qemu-devel@nongnu.org, qemu-arm@nongnu.org, Guoheyi , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 15, 2019 at 02:41:00PM +0100, Dave Martin wrote: > On Sat, Jul 13, 2019 at 05:53:57PM +0800, Guoheyi wrote: > > Hi folks, > > > > Do it make sense to implement virtual SDEI in qemu? So that we can have the > > standard way for guest to handle NMI watchdog, RAS events and something else > > which involves SDEI in a physical ARM64 machine. > > > > My basic idea is like below: > > > > 1. Change a few lines of code in kvm to allow unhandled SMC invocations > > (like SDEI) to be sent to qemu, with exit reason of KVM_EXIT_HYPERCALL, so > > we don't need to add new API. > > So long as KVM_EXIT_HYPERCALL reports sufficient information so that > userspace can identify the cause as an SMC and retrieve the SMC > immediate field, this seems feasible. > > For its own SMCCC APIs, KVM exclusively uses HVC, so rerouting SMC to > userspace shouldn't conflict. Be _very_ careful here! In systems without EL3 (and without NV), SMC UNDEFs rather than trapping to EL2. Given that, we shouldn't build a hypervisor ABI that depends on SMC. I am strongly of the opinion that (for !NV) we should always use HVC here and have KVM appropriately forward calls to userspace, rather than trying to use HVC/SMC to distinguish handled-by-kernel and handled-by-userspace events. For NV, the first guest hypervisor would use SMC to talk to KVM, all else being the same. > This bouncing of SMCs to userspace would need to be opt-in, otherwise > old userspace would see exits that it doesn't know what to do with. > > > 2. qemu handles supported SDEI calls just as the spec says for what a > > hypervisor should do for a guest OS. > > > > 3. For interrupts bound to hypervisor, qemu should stop injecting the IRQ to > > guest through KVM, but jump to the registered event handler directly, > > including context saving and restoring. Some interrupts like virtual timer > > are handled by kvm directly, so we may refuse to bind such interrupts to > > SDEI events. > > Something like that. > > Interactions between SDEI and PSCI would need some thought: for example, > after PSCI_CPU_ON, the newly online cpu needs to have SDEs masked. > > One option (suggested to me by James Morse) would be to allow userspace > to disable in the in-kernel PSCI implementation and provide its own > PSCI to the guest via SMC -- in which case userspace that wants to > implement SDEI would have to implement PSCI as well. I think this would be the best approach, since it puts userspace in charge of everything. However, this interacts poorly with FW-based mitigations that we implement in hyp. I suspect we'd probably need a mechanism to delegate that responsibility back to the kernel, and figure out if that has any interaction with thigns that got punted to userspace... Thanks, Mark.