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[209.132.183.28]) by mx.google.com with ESMTPS id l3si748244qtr.291.2019.03.11.00.21.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Mar 2019 00:21:50 -0700 (PDT) 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 21B0D30821F9; Mon, 11 Mar 2019 07:21:50 +0000 (UTC) Received: from [10.72.12.54] (ovpn-12-54.pek2.redhat.com [10.72.12.54]) by smtp.corp.redhat.com (Postfix) with ESMTP id EAD25611C3; Mon, 11 Mar 2019 07:21:43 +0000 (UTC) Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address To: Andrea Arcangeli Cc: Jerome Glisse , "Michael S. Tsirkin" , 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, Jan Kara 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> <20190307190910.GE3835@redhat.com> <20190307193838.GQ23850@redhat.com> <20190307201722.GG3835@redhat.com> <20190307212717.GS23850@redhat.com> <671c4a98-4699-836e-79fc-0ce650c7f701@redhat.com> <20190308191108.GA26923@redhat.com> From: Jason Wang Message-ID: <189b7839-3208-fb2e-4ac0-e6ca50e397bb@redhat.com> Date: Mon, 11 Mar 2019 15:21:41 +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: <20190308191108.GA26923@redhat.com> 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 [10.5.110.47]); Mon, 11 Mar 2019 07:21:50 +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 2019/3/9 上午3:11, Andrea Arcangeli wrote: > On Fri, Mar 08, 2019 at 05:13:26PM +0800, Jason Wang wrote: >> Actually not wrapping around,  the pages for used ring was marked as >> dirty after a round of virtqueue processing when we're sure vhost wrote >> something there. > Thanks for the clarification. So we need to convert it to > set_page_dirty and move it to the mmu notifier invalidate but in those > cases where gup_fast was called with write=1 (1 out of 3). > > If using ->invalidate_range the page pin also must be removed > immediately after get_user_pages returns (not ok to hold the pin in > vmap until ->invalidate_range is called) to avoid false positive gup > pin checks in things like KSM, or the pin must be released in > invalidate_range_start (which is called before the pin checks). > > Here's why: > > /* > * Check that no O_DIRECT or similar I/O is in progress on the > * page > */ > if (page_mapcount(page) + 1 + swapped != page_count(page)) { > set_pte_at(mm, pvmw.address, pvmw.pte, entry); > goto out_unlock; > } > [..] > set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry); > ^^^^^^^ too late release the pin here, the > above already failed > > ->invalidate_range cannot be used with mutex anyway so you need to go > back with invalidate_range_start/end anyway, just the pin must be > released in _start at the latest in such case. Yes. > > My prefer is generally to call gup_fast() followed by immediate > put_page() because I always want to drop FOLL_GET from gup_fast as a > whole to avoid 2 useless atomic ops per gup_fast. Ok, will do this (if I still plan to use vmap() in next version). > > I'll write more about vmap in answer to the other email. > > Thanks, > Andrea Thanks