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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 F0261C433DB for ; Tue, 29 Dec 2020 17:17:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C1182221F8 for ; Tue, 29 Dec 2020 17:17:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726420AbgL2RRZ (ORCPT ); Tue, 29 Dec 2020 12:17:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:45404 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726258AbgL2RRY (ORCPT ); Tue, 29 Dec 2020 12:17:24 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CC47A21D94; Tue, 29 Dec 2020 17:16:43 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kuIbx-004Ri2-Kb; Tue, 29 Dec 2020 17:16:41 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 29 Dec 2020 17:16:41 +0000 From: Marc Zyngier To: David Brazdil Cc: kvmarm@lists.cs.columbia.edu, James Morse , Julien Thierry , Suzuki K Poulose , Catalin Marinas , Will Deacon , Mark Rutland , Lorenzo Pieralisi , Sudeep Holla , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return In-Reply-To: <20201229160059.64135-1-dbrazdil@google.com> References: <20201229160059.64135-1-dbrazdil@google.com> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <229d84b8d7818a170adf489535ea2d43@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: dbrazdil@google.com, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, lorenzo.pieralisi@arm.com, sudeep.holla@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi David, On 2020-12-29 16:00, David Brazdil wrote: > The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET > should > not return, as dictated by the PSCI spec. However, there is firmware > out > there which breaks this assumption, leading to a hyp panic. Make KVM > more robust to broken firmware by allowing these to return. > > Signed-off-by: David Brazdil > --- > arch/arm64/kvm/hyp/nvhe/psci-relay.c | 13 +++++-------- > 1 file changed, 5 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c > b/arch/arm64/kvm/hyp/nvhe/psci-relay.c > index e3947846ffcb..8e7128cb7667 100644 > --- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c > +++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c > @@ -77,12 +77,6 @@ static unsigned long psci_forward(struct > kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 2), cpu_reg(host_ctxt, 3)); > } > > -static __noreturn unsigned long psci_forward_noreturn(struct > kvm_cpu_context *host_ctxt) > -{ > - psci_forward(host_ctxt); > - hyp_panic(); /* unreachable */ > -} > - > static unsigned int find_cpu_id(u64 mpidr) > { > unsigned int i; > @@ -251,10 +245,13 @@ static unsigned long psci_0_2_handler(u64 > func_id, struct kvm_cpu_context *host_ > case PSCI_0_2_FN_MIGRATE_INFO_TYPE: > case PSCI_0_2_FN64_MIGRATE_INFO_UP_CPU: > return psci_forward(host_ctxt); > + /* > + * SYSTEM_OFF/RESET should not return according to the spec. > + * Allow it so as to stay robust to broken firmware. > + */ > case PSCI_0_2_FN_SYSTEM_OFF: > case PSCI_0_2_FN_SYSTEM_RESET: > - psci_forward_noreturn(host_ctxt); > - unreachable(); > + return psci_forward(host_ctxt); > case PSCI_0_2_FN64_CPU_SUSPEND: > return psci_cpu_suspend(func_id, host_ctxt); > case PSCI_0_2_FN64_CPU_ON: Thanks for having tracked this. I wonder whether we should also taint the kernel in this case, because this is completely unexpected, and a major spec violation. Ideally, we'd be able to detect this case and prevent pKVM from getting initialised at all, but I guess there is no way to detect the sucker without ... calling SYSTEM_RESET? M. -- Jazz is not dead. It just smells funny...