From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Date: Thu, 7 Mar 2019 10:47:22 -0500 Message-ID: <20190307103503-mutt-send-email-mst@kernel.org> References: <1551856692-3384-1-git-send-email-jasowang@redhat.com> <1551856692-3384-6-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <1551856692-3384-6-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, Mar 06, 2019 at 02:18:12AM -0500, Jason Wang wrote: > +static const struct mmu_notifier_ops vhost_mmu_notifier_ops = { > + .invalidate_range = vhost_invalidate_range, > +}; > + > void vhost_dev_init(struct vhost_dev *dev, > struct vhost_virtqueue **vqs, int nvqs, int iov_limit) > { I also wonder here: when page is write protected then it does not look like .invalidate_range is invoked. E.g. mm/ksm.c calls mmu_notifier_invalidate_range_start and mmu_notifier_invalidate_range_end but not mmu_notifier_invalidate_range. Similarly, rmap in page_mkclean_one will not call mmu_notifier_invalidate_range. If I'm right vhost won't get notified when page is write-protected since you didn't install start/end notifiers. Note that end notifier can be called with page locked, so it's not as straight-forward as just adding a call. Writing into a write-protected page isn't a good idea. Note that documentation says: it is fine to delay the mmu_notifier_invalidate_range call to mmu_notifier_invalidate_range_end() outside the page table lock. implying it's called just later. -- MST