Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754801AbdLGPoL (ORCPT ); Thu, 7 Dec 2017 10:44:11 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:54372 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754654AbdLGPoI (ORCPT ); Thu, 7 Dec 2017 10:44:08 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 424D860218 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=nleeder@codeaurora.org Cc: nleeder@codeaurora.org, Mark Rutland , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Mark Langsdorf , Mark Salter , Jon Masters , Timur Tabi , Mark Brown Subject: Re: [PATCH] perf: qcom_l2_pmu: don't allow guest access To: Will Deacon References: <1512575733-923-1-git-send-email-nleeder@codeaurora.org> <20171206161149.ezlzzcuvxbot5tio@lakrids.cambridge.arm.com> <20171207133812.GG31900@arm.com> From: "Leeder, Neil" Message-ID: Date: Thu, 7 Dec 2017 10:44:04 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171207133812.GG31900@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1876 Lines: 43 On 12/7/2017 8:38 AM, Will Deacon wrote: > On Wed, Dec 06, 2017 at 04:19:24PM -0500, Leeder, Neil wrote: >> On 12/6/2017 11:11 AM, Mark Rutland wrote: >>> On Wed, Dec 06, 2017 at 10:55:33AM -0500, Neil Leeder wrote: >>>> Guests cannot access IMPDEF system registers, which are used >>>> by this driver. Disable the driver if it's running in a guest VM. >>>> >>>> Signed-off-by: Neil Leeder >>>> --- >>>> drivers/perf/qcom_l2_pmu.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>> >>> I'm a little confused by this. Why is this hypervisor providing a >>> QCOM8130 device to the guest that it cannot use? >>> >>> Could you elaborate on what's going on? >>> >> >> While there's an argument that the guest shouldn't be loading the driver >> in the first place, we can't control everyone's guest configuration or what >> their hypervisor does. > > Ok, but why is the hypervisor advertising a device that effectively doesn't > exist? Most drivers trust the firmware tables they are given, so this makes > it sound like we should start annotating all drivers for devices that we > don't expect to see in a guest with is_hyp_mode_available() checks. > > That doesn't feel quite right to me. Hi Will, I suspect that most mis-configured drivers don't fail until they're used, or are otherwise Mostly Harmless. The problem here is that this driver uses IMPDEF system registers in its init, and I'd guess only a minority of drivers do that. So it crashed the kernel with an illegal instruction on boot. I'm trying to be a good citizen here and not allow my driver to stop a kernel from booting because someone misconfigured something out of my control. Neil -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.