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=-1.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,SUBJ_ALL_CAPS,USER_AGENT_SANE_1 autolearn=no 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 81644C10F14 for ; Thu, 3 Oct 2019 15:44:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52E7C2133F for ; Thu, 3 Oct 2019 15:44:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728564AbfJCPn7 (ORCPT ); Thu, 3 Oct 2019 11:43:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40122 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727024AbfJCPn7 (ORCPT ); Thu, 3 Oct 2019 11:43:59 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CD2AD3082231; Thu, 3 Oct 2019 15:43:58 +0000 (UTC) Received: from redhat.com (ovpn-112-54.rdu2.redhat.com [10.10.112.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3DB7119C69; Thu, 3 Oct 2019 15:43:49 +0000 (UTC) Date: Thu, 3 Oct 2019 11:42:33 -0400 From: Jerome Glisse To: Paolo Bonzini Cc: Mircea CIRJALIU - MELIU , Adalbert =?utf-8?B?TGF6xINy?= , Matthew Wilcox , "kvm@vger.kernel.org" , "linux-mm@kvack.org" , "virtualization@lists.linux-foundation.org" , Radim =?utf-8?B?S3LEjW3DocWZ?= , Konrad Rzeszutek Wilk , Tamas K Lengyel , Mathieu Tarral , Samuel =?iso-8859-1?Q?Laur=E9n?= , Patrick Colp , Jan Kiszka , Stefan Hajnoczi , Weijiang Yang , Yu C , Mihai =?utf-8?B?RG9uyJt1?= Subject: Re: DANGER WILL ROBINSON, DANGER Message-ID: <20191003154233.GA4421@redhat.com> References: <20190905180955.GA3251@redhat.com> <5b0966de-b690-fb7b-5a72-bc7906459168@redhat.com> <20191002192714.GA5020@redhat.com> <20191002141542.GA5669@redhat.com> <20191002170429.GA8189@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Thu, 03 Oct 2019 15:43:59 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Oct 02, 2019 at 10:10:18PM +0200, Paolo Bonzini wrote: > On 02/10/19 19:04, Jerome Glisse wrote: > > On Wed, Oct 02, 2019 at 06:18:06PM +0200, Paolo Bonzini wrote: > >>>> If the mapping of the source VMA changes, mirroring can update the > >>>> target VMA via insert_pfn. But what ensures that KVM's MMU notifier > >>>> dismantles its own existing page tables (so that they can be recreated > >>>> with the new mapping from the source VMA)? > >> > >> The KVM inspector process is also (or can be) a QEMU that will have to > >> create its own KVM guest page table. So if a page in the source VMA is > >> unmapped we want: > >> > >> - the source KVM to invalidate its guest page table (done by the KVM MMU > >> notifier) > >> > >> - the target VMA to be invalidated (easy using mirroring) > >> > >> - the target KVM to invalidate its guest page table, as a result of > >> invalidation of the target VMA > > > > You can do the target KVM invalidation inside the mirroring invalidation > > code. > > Why should the source and target KVMs behave differently? If the source > invalidates its guest page table via MMU notifiers, so should the target. > > The KVM MMU notifier exists so that nothing (including mirroring) needs > to know that there is KVM on the other side. Any interaction between > KVM page tables and VMAs must be mediated by MMU notifiers, anything > else is unacceptable. > > If it is possible to invoke the MMU notifiers around the calls to > insert_pfn, that of course would be perfect. Ok and yes you can do that exactly ie inside the mmu notifier callback from the target. For instance it is as easy as: target_mirror_notifier_start_callback(start, end) { struct kvm_mirror_struct *kvmms = from_mmun(...); unsigned long target_foff, size; size = end - start; target_foff = kvmms_convert_mirror_address(start); take_lock(kvmms->mirror_fault_exclusion_lock); unmap_mapping_range(kvmms->address_space, target_foff, size, 1); drop_lock(kvmms->mirror_fault_exclusion_lock); } All that is needed is to make sure that vm_normal_page() will see those pte (inside the process that is mirroring the other process) as special which is the case either because insert_pfn() mark the pte as special or the kvm device driver which control the vm_operation struct set a find_special_page() callback that always return NULL, or the vma has either VM_PFNMAP or VM_MIXEDMAP set (which is the case with insert_pfn). So you can keep the existing kvm code unmodified. Cheers, Jérôme