From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: DANGER WILL ROBINSON, DANGER Date: Wed, 2 Oct 2019 13:04:29 -0400 Message-ID: <20191002170429.GA8189@redhat.com> References: <20190815191929.GA9253@redhat.com> <20190815201630.GA25517@redhat.com> <20190905180955.GA3251@redhat.com> <5b0966de-b690-fb7b-5a72-bc7906459168@redhat.com> <20191002192714.GA5020@redhat.com> <20191002141542.GA5669@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Paolo Bonzini Cc: Tamas K Lengyel , Weijiang Yang , Yu C , "kvm@vger.kernel.org" , Radim =?utf-8?B?S3LEjW3DocWZ?= , Jan Kiszka , Samuel =?iso-8859-1?Q?Laur=E9n?= , Konrad Rzeszutek Wilk , Matthew Wilcox , "virtualization@lists.linux-foundation.org" , Adalbert =?utf-8?B?TGF6xINy?= , "linux-mm@kvack.org" , Patrick Colp , Mathieu Tarral , Stefan Hajnoczi , Mircea CIRJALIU - MELIU , Mihai =?utf-8?B?RG9uyJt1?= List-Id: virtualization@lists.linuxfoundation.org On Wed, Oct 02, 2019 at 06:18:06PM +0200, Paolo Bonzini wrote: > On 02/10/19 16:15, Jerome Glisse wrote: > >>> Why would you need to target mmu notifier on target vma ? > >> 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)? > >> > > So just to make sure i follow we have: > > - qemu process on host with anonymous vma > > -> host cpu page table > > - kvm which maps host anonymous vma to guest > > -> kvm guest page table > > - kvm inspector process which mirror vma from qemu process > > -> inspector process page table > > = > > AFAIK the KVM notifier's will clear the kvm guest page table whenever > > necessary (through kvm_mmu_notifier_invalidate_range_start). This is > > what ensure that KVM's dismatles its own mapping, it abides to mmu- > > notifier callbacks. If you did not you would have bugs (at least i > > expect so). Am i wrong here ? > = > The KVM inspector process is also (or can be) a QEMU that will have to > create its own KVM guest page table. Ok missed that part, thank you for explaining > = > 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. Cheers, J=E9r=F4me