From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Masters Subject: Re: [PATCH 3/3] arm, arm64: KVM: handle potential incoherency of readonly memslots Date: Thu, 20 Nov 2014 14:49:54 -0500 Message-ID: <546E45E2.1030002@redhat.com> References: <1416236333-9378-1-git-send-email-ard.biesheuvel@linaro.org> <1416236333-9378-3-git-send-email-ard.biesheuvel@linaro.org> <546A146E.1020804@redhat.com> <546A1905.6080607@redhat.com> <546D288F.1040107@samsung.com> <546DA19B.5050306@redhat.com> <546E3489.2050809@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Laszlo Ersek , kvm-devel , Ard Biesheuvel , Paolo Bonzini , "kvmarm@lists.cs.columbia.edu" To: Peter Maydell , Mario Smarduch Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36030 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756658AbaKTTuD (ORCPT ); Thu, 20 Nov 2014 14:50:03 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 11/20/2014 01:40 PM, Peter Maydell wrote: > On 20 November 2014 18:35, Mario Smarduch wrote: >> I think beyond consistency, there should be no double mappings with >> conflicting attributes at any time or CPU state is undefined. > > The situation is not so bleak as this. See section B2.9 "Mismatched > memory attributes" in the ARMv8 ARM ARM (DDI0487A.d), which lays > out in some detail what the results of mismatched attributes are > (generally, you lose ordering or coherency guarantees you might > have hoped to have). They're not pretty, but it's not as bad > as completely UNPREDICTABLE behaviour. Quick side note that I did raise exactly this issue with the ARM Architecture team several years ago (that of missmatched memory attributes between a guest and hypervisor) and it is a known concern. I'm personally concerned about a couple of things that I won't go into here but will followup on what the longer term plan might be. Jon.