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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 81AFDC4360C for ; Mon, 4 Jan 2021 16:09:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 696E1205CA for ; Mon, 4 Jan 2021 16:09:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729620AbhADQIw (ORCPT ); Mon, 4 Jan 2021 11:08:52 -0500 Received: from mail.kernel.org ([198.145.29.99]:44142 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729610AbhADQIu (ORCPT ); Mon, 4 Jan 2021 11:08:50 -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 DB4C420665; Mon, 4 Jan 2021 16:08:09 +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 1kwSOt-005FxL-4b; Mon, 04 Jan 2021 16:08:07 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 04 Jan 2021 16:08:07 +0000 From: Marc Zyngier To: Qian Cai Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, Stephen Rothwell , Linux Next Mailing List , Alexandru Elisei Subject: Re: [PATCH] KVM: arm64: Don't access PMCR_EL0 when no PMU is available In-Reply-To: <703e1b5f2db1631e8f9c55619909fe66eb069f25.camel@redhat.com> References: <20201210083059.1277162-1-maz@kernel.org> <703e1b5f2db1631e8f9c55619909fe66eb069f25.camel@redhat.com> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <579c839a0016107af66e704f147f9814@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: qcai@redhat.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, sfr@canb.auug.org.au, linux-next@vger.kernel.org, alexandru.elisei@arm.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-next@vger.kernel.org On 2021-01-04 15:47, Qian Cai wrote: > On Thu, 2020-12-10 at 08:30 +0000, Marc Zyngier wrote: >> We reset the guest's view of PMCR_EL0 unconditionally, based on >> the host's view of this register. It is however legal for an >> imnplementation not to provide any PMU, resulting in an UNDEF. >> >> The obvious fix is to skip the reset of this shadow register >> when no PMU is available, sidestepping the issue entirely. >> If no PMU is available, the guest is not able to request >> a virtual PMU anyway, so not doing nothing is the right thing >> to do! >> >> It is unlikely that this bug can hit any HW implementation >> though, as they all provide a PMU. It has been found using nested >> virt with the host KVM not implementing the PMU itself. >> >> Fixes: ab9468340d2bc ("arm64: KVM: Add access handler for PMCR >> register") >> Signed-off-by: Marc Zyngier > > Reverting this commit on the top of today's linux-next fixed a qemu-kvm > coredump > issue on TX2 while starting a guest. > > - host kernel .config: > https://cailca.coding.net/public/linux/mm/git/files/master/arm64.config > > # /usr/libexec/qemu-kvm -name ubuntu-20.04-server-cloudimg -cpu host > -smp 2 -m 2g > -drive > if=none,format=qcow2,file=./ubuntu-20.04-server-cloudimg.qcow2,id=hd > -device virtio-scsi -device scsi-hd,drive=hd -cdrom > ./ubuntu-20.04-server-cloudimg.iso > -bios /usr/share/AAVMF/AAVMF_CODE.fd -M gic-version=host -nographic > -nic user,model=virtio,hostfwd=tcp::2222-:22 > > qemu-kvm: /builddir/build/BUILD/qemu-4.2.0/target/arm/helper.c:1812: > pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed. You don't have KVM_ARM_PMU selected in your config, so QEMU cannot access the PMU registers, and no counters are exposed. M. -- Jazz is not dead. It just smells funny...