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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 0350EC38A2A for ; Fri, 8 May 2020 06:45:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA14920746 for ; Fri, 8 May 2020 06:44:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Rz/6BM5o" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726942AbgEHGo7 (ORCPT ); Fri, 8 May 2020 02:44:59 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:40496 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725971AbgEHGo6 (ORCPT ); Fri, 8 May 2020 02:44:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588920297; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ldgRmfrU61jak98QbW+ZRtHuHZaSuicPr557G5QWVUo=; b=Rz/6BM5o9Wn/WJ4WOgogGGeaUBae39WvJalA+rCCvU9VhtTl6joZ8nHU4tOiFWpytwZfRw Nz0+gRopweNAmJUTQxat7Vv6Ajs0ZJhfbf3pyQXNWGRisGafSU9018VvqO3g7AZwMdysvz fwlSvE7X0YjYZnhBiYARFWWSGvED0cA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-514-xbTrrzdBMpeHOn8_IOa8PA-1; Fri, 08 May 2020 02:44:55 -0400 X-MC-Unique: xbTrrzdBMpeHOn8_IOa8PA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C698D1B18BC6; Fri, 8 May 2020 06:44:53 +0000 (UTC) Received: from [10.72.13.98] (ovpn-13-98.pek2.redhat.com [10.72.13.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id 96B2810429AF; Fri, 8 May 2020 06:44:46 +0000 (UTC) Subject: Re: [PATCH v2 2/3] vfio-pci: Fault mmaps to enable vma tracking To: Peter Xu , Jason Gunthorpe Cc: Alex Williamson , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, cohuck@redhat.com References: <158871401328.15589.17598154478222071285.stgit@gimli.home> <158871569380.15589.16950418949340311053.stgit@gimli.home> <20200507214744.GP228260@xz-x1> <20200507160334.4c029518@x1.home> <20200507222223.GR228260@xz-x1> <20200507235633.GL26002@ziepe.ca> <20200508021656.GS228260@xz-x1> From: Jason Wang Message-ID: <0ee2fd04-d544-d03b-0a7c-90c22275aac9@redhat.com> Date: Fri, 8 May 2020 14:44:44 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200508021656.GS228260@xz-x1> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/5/8 上午10:16, Peter Xu wrote: > On Thu, May 07, 2020 at 08:56:33PM -0300, Jason Gunthorpe wrote: >> On Thu, May 07, 2020 at 06:22:23PM -0400, Peter Xu wrote: >>> On Thu, May 07, 2020 at 04:03:34PM -0600, Alex Williamson wrote: >>>> On Thu, 7 May 2020 17:47:44 -0400 >>>> Peter Xu wrote: >>>> >>>>> Hi, Alex, >>>>> >>>>> On Tue, May 05, 2020 at 03:54:53PM -0600, Alex Williamson wrote: >>>>>> +/* >>>>>> + * Zap mmaps on open so that we can fault them in on access and therefore >>>>>> + * our vma_list only tracks mappings accessed since last zap. >>>>>> + */ >>>>>> +static void vfio_pci_mmap_open(struct vm_area_struct *vma) >>>>>> +{ >>>>>> + zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start); >>>>> A pure question: is this only a safety-belt or it is required in some known >>>>> scenarios? >>>> It's not required. I originally did this so that I'm not allocating a >>>> vma_list entry in a path where I can't return error, but as Jason >>>> suggested I could zap here only in the case that I do encounter that >>>> allocation fault. However I still like consolidating the vma_list >>>> handling to the vm_ops .fault and .close callbacks and potentially we >>>> reduce the zap latency by keeping the vma_list to actual users, which >>>> we'll get to eventually anyway in the VM case as memory BARs are sized >>>> and assigned addresses. >>> Yes, I don't see much problem either on doing the vma_list maintainance only in >>> .fault() and .close(). My understandingg is that the worst case is the perf >>> critical applications (e.g. DPDK) could pre-fault these MMIO region easily >>> during setup if they want. My question was majorly about whether the vma >>> should be guaranteed to have no mapping at all when .open() is called. But I >>> agree with you that it's always good to have that as safety-belt anyways. >> If the VMA has a mapping then that specific VMA has to be in the >> linked list. >> >> So if the zap is skipped then the you have to allocate something and >> add to the linked list to track the VMA with mapping. >> >> It is not a 'safety belt' > But shouldn't open() only be called when the VMA is created for a memory range? > If so, does it also mean that the address range must have not been mapped yet? Probably not, e.g when VMA is being split. Thanks > > Thanks, >