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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 F1D6AC3A5A5 for ; Thu, 5 Sep 2019 08:04:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C686A21743 for ; Thu, 5 Sep 2019 08:04:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567670642; bh=U2pBcUJ3BvaUQ2N2u+JAYhiN+c5dz40RzByi9j17gGM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=lpyzIf8DUv5NEHI6BHLqQPk9ldlBI97JYJaDkZ7jzPqwufB2nu9bTN/ocZAaBx8Jh 1meOPi1Eu9Y4xrloAMliRFw1w3ATTJCy71/uusDuE40She+ptgj6N79bBljWNqWrgA ksnSDSX27bmcb7mEfATEiDghgiqfkcc8NT7RHoyM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732205AbfIEIEB (ORCPT ); Thu, 5 Sep 2019 04:04:01 -0400 Received: from foss.arm.com ([217.140.110.172]:38830 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730991AbfIEIEB (ORCPT ); Thu, 5 Sep 2019 04:04:01 -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 94B5928; Thu, 5 Sep 2019 01:04:00 -0700 (PDT) Received: from big-swifty.misterjones.org (unknown [10.1.27.38]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5AA793F67D; Thu, 5 Sep 2019 01:03:58 -0700 (PDT) Date: Thu, 05 Sep 2019 09:03:50 +0100 Message-ID: <86r24vrwyh.wl-maz@kernel.org> From: Marc Zyngier To: Heinrich Schuchardt Cc: James Morse , Julien Thierry , Suzuki K Pouloze , Peter Maydell , Stefan Hajnoczi , =?UTF-8?B?IkRhbmllbCBQIC4gQmVycmFuZ8OpIg==?= , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] KVM: inject data abort if instruction cannot be decoded In-Reply-To: <20190904180736.29009-1-xypron.glpk@gmx.de> References: <20190904180736.29009-1-xypron.glpk@gmx.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Please use my kernel.org address. My arm.com address will disappear shortly] On Wed, 04 Sep 2019 19:07:36 +0100, Heinrich Schuchardt wrote: > > If an application tries to access memory that is not mapped, an error > ENOSYS, "load/store instruction decoding not implemented" may occur. > QEMU will hang with a register dump. > > Instead create a data abort that can be handled gracefully by the > application running in the virtual environment. > > Now the virtual machine can react to the event in the most appropriate > way - by recovering, by writing an informative log, or by rebooting. > > Signed-off-by: Heinrich Schuchardt > --- > virt/kvm/arm/mmio.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c > index a8a6a0c883f1..0cbed7d6a0f4 100644 > --- a/virt/kvm/arm/mmio.c > +++ b/virt/kvm/arm/mmio.c > @@ -161,8 +161,8 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run, > if (ret) > return ret; > } else { > - kvm_err("load/store instruction decoding not implemented\n"); > - return -ENOSYS; > + kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu)); > + return 1; How can you tell that the access would fault? You have no idea at that stage (the kernel doesn't know about the MMIO ranges that userspace handles). All you know is that you're faced with a memory access that you cannot emulate in the kernel. Injecting a data abort at that stage is not something that the architecture allows. If you want to address this, consider forwarding the access to userspace. You'll only need an instruction decoder (supporting T1, T2, A32 and A64) and a S1 page table walker (one per page table format, all three of them) to emulate the access (having taken care of stopping all the other vcpus to make sure there is no concurrent modification of the page tables). You'll then be able to return the result of the access back to the kernel. Of course, the best thing would be to actually fix the guest so that it doesn't use non-emulatable MMIO accesses. In general, that the sign of a bug in low-level accessors. M. -- Jazz is not dead, it just smells funny.