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[209.132.183.28]) by mx.google.com with ESMTPS id l81si2119455qke.236.2019.03.08.00.31.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Mar 2019 00:31:39 -0800 (PST) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E0B2310C6C; Fri, 8 Mar 2019 08:31:38 +0000 (UTC) Received: from [10.72.12.27] (ovpn-12-27.pek2.redhat.com [10.72.12.27]) by smtp.corp.redhat.com (Postfix) with ESMTP id C3731611D1; Fri, 8 Mar 2019 08:31:31 +0000 (UTC) Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address To: "Michael S. Tsirkin" 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 References: <1551856692-3384-1-git-send-email-jasowang@redhat.com> <1551856692-3384-6-git-send-email-jasowang@redhat.com> <20190306092837-mutt-send-email-mst@kernel.org> <15105894-4ec1-1ed0-1976-7b68ed9eeeda@redhat.com> <20190307101708-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <92dfa6cc-a86c-0cef-6384-98aeb8b9e567@redhat.com> Date: Fri, 8 Mar 2019 16:31:29 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190307101708-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 08 Mar 2019 08:31:38 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2019/3/7 下午11:34, Michael S. Tsirkin wrote: > On Thu, Mar 07, 2019 at 10:45:57AM +0800, Jason Wang wrote: >> On 2019/3/7 上午12:31, Michael S. Tsirkin wrote: >>>> +static void vhost_set_vmap_dirty(struct vhost_vmap *used) >>>> +{ >>>> + int i; >>>> + >>>> + for (i = 0; i < used->npages; i++) >>>> + set_page_dirty_lock(used->pages[i]); >>> This seems to rely on page lock to mark page dirty. >>> >>> Could it happen that page writeback will check the >>> page, find it clean, and then you mark it dirty and then >>> invalidate callback is called? >>> >>> >> Yes. But does this break anything? >> The page is still there, we just remove a >> kernel mapping to it. >> >> Thanks > Yes it's the same problem as e.g. RDMA: > we've just marked the page as dirty without having buffers. > Eventually writeback will find it and filesystem will complain... > So if the pages are backed by a non-RAM-based filesystem, it’s all just broken. Yes, we can't depend on the pages that might have been invalidated. As suggested, the only suitable place is the MMU notifier callbacks. Thanks > one can hope that RDMA guys will fix it in some way eventually. > For now, maybe add a flag in e.g. VMA that says that there's no > writeback so it's safe to mark page dirty at any point? > > > > >