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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 CA244C43142 for ; Thu, 2 Aug 2018 13:30:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DBC9214F1 for ; Thu, 2 Aug 2018 13:30:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7DBC9214F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387536AbeHBPVb (ORCPT ); Thu, 2 Aug 2018 11:21:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:46080 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387426AbeHBPVb (ORCPT ); Thu, 2 Aug 2018 11:21:31 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9CE74402242D; Thu, 2 Aug 2018 13:30:17 +0000 (UTC) Received: from vitty.brq.redhat.com.redhat.com (unknown [10.43.2.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 860C9213ED6A; Thu, 2 Aug 2018 13:30:16 +0000 (UTC) From: Vitaly Kuznetsov To: Paolo Bonzini Cc: Jim Mattson , kvm list , Radim =?utf-8?B?S3LEjW3DocWZ?= , the arch/x86 maintainers , LKML Subject: Re: [PATCH RFC] x86/kvm/lapic: always disable MMIO interface in x2APIC mode References: <20180727144448.9606-1-vkuznets@redhat.com> <87sh41nkz5.fsf@vitty.brq.redhat.com> Date: Thu, 02 Aug 2018 15:30:15 +0200 In-Reply-To: (Paolo Bonzini's message of "Thu, 2 Aug 2018 13:54:51 +0200") Message-ID: <87wot899qw.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Thu, 02 Aug 2018 13:30:17 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Thu, 02 Aug 2018 13:30:17 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'vkuznets@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 30/07/2018 11:14, Vitaly Kuznetsov wrote: >> Paolo Bonzini writes: >> >>> On 27/07/2018 18:48, Jim Mattson wrote: >>>> On a physical machine, I would expect the default local APIC page to >>>> fall in the PCI hole, so it would be correct to sink writes and to >>>> return all ones for reads. Does qemu implement a PCI hole, and does >>>> this address fall into it? >>> >>> It does implement a PCI hole, but when using the kernel LAPIC it expects >>> that only devices write to that range; therefore that address doesn't >>> fall into the PCI hole, and instead it generates an MSIs. >> >> Yes, and that's why I believe it's correct to never forward lapic >> reads/writes from KVM to userspace when lapic is in kernel. >> >> "RFC" was mostly about the inconsistency with the case when APIC access >> page is in use. To be 100% correct I would suggest to somehow make it >> behave like MMIO hole in case we're in x2APIC/disabled mode too. >> > > FWIW it is possible to move the MSI memory region from system memory to > the PCI address space in QEMU, however I'm worried about backwards > compatibility. > You know better :-) > Vitaly, perhaps you could resubmit this patch, and provide a > KVM_CAP_DISABLE_QUIRKS switch that would make apic_mmio_{read,write} > return -EOPNOTSUPP in this case? Just to make sure I understand, we introduce a KVM_QUIRK_LAPIC_DISABLED_MMIO bit and will be emulating MMIO hole in KVM till Qemu is able to deal with reads/writes passed to it correctly? -- Vitaly