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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 923B8C433E0 for ; Thu, 25 Feb 2021 10:21:08 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0C1CD64EAF for ; Thu, 25 Feb 2021 10:21:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0C1CD64EAF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54984 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lFDla-0001Tk-TA for qemu-devel@archiver.kernel.org; Thu, 25 Feb 2021 05:21:06 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:40028) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lFDkT-0000WM-Pl for qemu-devel@nongnu.org; Thu, 25 Feb 2021 05:19:57 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:60943) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lFDkP-0003Iw-U0 for qemu-devel@nongnu.org; Thu, 25 Feb 2021 05:19:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614248393; 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: in-reply-to:in-reply-to:references:references; bh=P0BCu9jEH3lkjIa2EeyV1ix7q8WeRvH20CqIpoMmeWY=; b=iqtjmzjuAI1i2VcoPWOVEKLZS6AoU7HtcXnhZ3+J6BLHYocyjf6F1MP2fJ40oKFiHzmPGG Od/A8iRbsfFKxggKfSna/lxzEtOTJ30ZKZ2kzqWs9orA2zGw1vrLiie6o4agGmMm2IX8Ip eXkD35zSpoFhr2vv5am1hV5vPWvPPxQ= 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-447-WGz4vnErN_u_HPZVnfvOAw-1; Thu, 25 Feb 2021 05:19:48 -0500 X-MC-Unique: WGz4vnErN_u_HPZVnfvOAw-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 82A90100B3B2 for ; Thu, 25 Feb 2021 10:19:47 +0000 (UTC) Received: from work-vm (ovpn-114-227.ams2.redhat.com [10.36.114.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B7F646E51F; Thu, 25 Feb 2021 10:19:33 +0000 (UTC) Date: Thu, 25 Feb 2021 10:19:31 +0000 From: "Dr. David Alan Gilbert" To: Stefan Hajnoczi Subject: Re: [PATCH 18/24] DAX/unmap virtiofsd: Parse unmappable elements Message-ID: References: <20210209190224.62827-1-dgilbert@redhat.com> <20210209190224.62827-19-dgilbert@redhat.com> <20210211142948.GS247031@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20210211142948.GS247031@stefanha-x1.localdomain> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs@redhat.com, marcandre.lureau@redhat.com, qemu-devel@nongnu.org, vgoyal@redhat.com, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Stefan Hajnoczi (stefanha@redhat.com) wrote: > On Tue, Feb 09, 2021 at 07:02:18PM +0000, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > For some read/writes the virtio queue elements are unmappable by > > the daemon; these are cases where the data is to be read/written > > from non-RAM. In viritofs's case this is typically a direct read/write > > into an mmap'd DAX file also on virtiofs (possibly on another instance). > > > > When we receive a virtio queue element, check that we have enough > > mappable data to handle the headers. Make a note of the number of > > unmappable 'in' entries (ie. for read data back to the VMM), > > and flag the fuse_bufvec for 'out' entries with a new flag > > FUSE_BUF_PHYS_ADDR. > > Looking back at this I think vhost-user will need generic > READ_MEMORY/WRITE_MEMORY commands. It's okay for virtio-fs to have its > own IO command (although not strictly necessary). > > With generic READ_MEMORY/WRITE_MEMORY libvhost-user and other vhost-user > device backend implementations can handle vring descriptors that point > into the DAX window. This can be done transparently so individual device > implementations (net, blk, etc) don't even know when memory is copied vs > zero-copy shared memory access. > > So this approach is okay for virtio-fs but it's not a long-term solution > for all of vhost-user. Eventually the long-term solution may be needed > so that other VIRTIO devices that have shared memory resources work. > > Another bonus of READ_MEMORY/WRITE_MEMORY is that users that prefer an > enforcing vIOMMU can disable shared memory (maybe just keep the vring > itself mmapped). > > I just wanted to share this idea but don't expect it to be addressed in > this patch series. Yes, that would be nice; although in this case it would imply an extra memory copy; you'd have to do the IO in the daemon, and then perform a read/write back across the socket. > > diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h > > index a090040bb2..ed9280de91 100644 > > --- a/tools/virtiofsd/fuse_common.h > > +++ b/tools/virtiofsd/fuse_common.h > > @@ -611,6 +611,13 @@ enum fuse_buf_flags { > > * detected. > > */ > > FUSE_BUF_FD_RETRY = (1 << 3), > > + > > + /** > > + * The addresses in the iovec represent guest physical addresses > > + * that can't be mapped by the daemon process. > > + * IO must be bounced back to the VMM to do it. > > + */ > > + FUSE_BUF_PHYS_ADDR = (1 << 4), > > With a vIOMMU it's an IOVA. Without a vIOMMU it's a GPA. This constant > may need to be renamed in the future, but it is okay for now. Do we have any naming for something that's either a GPA or a IOVA? > > + if (req->bad_in_num || req->bad_out_num) { > > + bool handled_unmappable = false; > > + > > + if (out_num > 2 && out_num_readable >= 2 && !req->bad_in_num && > > + out_sg[0].iov_len == sizeof(struct fuse_in_header) && > > + ((struct fuse_in_header *)fbuf.mem)->opcode == FUSE_WRITE && > > + out_sg[1].iov_len == sizeof(struct fuse_write_in)) { > > This violates the VIRTIO specification: > > 2.6.4.1 Device Requirements: Message Framing > > The device MUST NOT make assumptions about the particular arrangement of descriptors. > > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-280004 > > The driver is not obligated to submit separate iovecs. out_num == 1 is > valid and the device needs to process it byte-wise instead of making > assumptions about iovec layout. Yes, it's actually not new in this patch, but I'll clean it up. I took the shortcut all the way back in: e17f7a580e2c599330ad virtiofsd: Pass write iov's all the way through Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 25 Feb 2021 10:19:31 +0000 From: "Dr. David Alan Gilbert" Message-ID: References: <20210209190224.62827-1-dgilbert@redhat.com> <20210209190224.62827-19-dgilbert@redhat.com> <20210211142948.GS247031@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210211142948.GS247031@stefanha-x1.localdomain> Subject: Re: [Virtio-fs] [PATCH 18/24] DAX/unmap virtiofsd: Parse unmappable elements List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: virtio-fs@redhat.com, marcandre.lureau@redhat.com, qemu-devel@nongnu.org, vgoyal@redhat.com, mst@redhat.com * Stefan Hajnoczi (stefanha@redhat.com) wrote: > On Tue, Feb 09, 2021 at 07:02:18PM +0000, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > For some read/writes the virtio queue elements are unmappable by > > the daemon; these are cases where the data is to be read/written > > from non-RAM. In viritofs's case this is typically a direct read/write > > into an mmap'd DAX file also on virtiofs (possibly on another instance). > > > > When we receive a virtio queue element, check that we have enough > > mappable data to handle the headers. Make a note of the number of > > unmappable 'in' entries (ie. for read data back to the VMM), > > and flag the fuse_bufvec for 'out' entries with a new flag > > FUSE_BUF_PHYS_ADDR. > > Looking back at this I think vhost-user will need generic > READ_MEMORY/WRITE_MEMORY commands. It's okay for virtio-fs to have its > own IO command (although not strictly necessary). > > With generic READ_MEMORY/WRITE_MEMORY libvhost-user and other vhost-user > device backend implementations can handle vring descriptors that point > into the DAX window. This can be done transparently so individual device > implementations (net, blk, etc) don't even know when memory is copied vs > zero-copy shared memory access. > > So this approach is okay for virtio-fs but it's not a long-term solution > for all of vhost-user. Eventually the long-term solution may be needed > so that other VIRTIO devices that have shared memory resources work. > > Another bonus of READ_MEMORY/WRITE_MEMORY is that users that prefer an > enforcing vIOMMU can disable shared memory (maybe just keep the vring > itself mmapped). > > I just wanted to share this idea but don't expect it to be addressed in > this patch series. Yes, that would be nice; although in this case it would imply an extra memory copy; you'd have to do the IO in the daemon, and then perform a read/write back across the socket. > > diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h > > index a090040bb2..ed9280de91 100644 > > --- a/tools/virtiofsd/fuse_common.h > > +++ b/tools/virtiofsd/fuse_common.h > > @@ -611,6 +611,13 @@ enum fuse_buf_flags { > > * detected. > > */ > > FUSE_BUF_FD_RETRY = (1 << 3), > > + > > + /** > > + * The addresses in the iovec represent guest physical addresses > > + * that can't be mapped by the daemon process. > > + * IO must be bounced back to the VMM to do it. > > + */ > > + FUSE_BUF_PHYS_ADDR = (1 << 4), > > With a vIOMMU it's an IOVA. Without a vIOMMU it's a GPA. This constant > may need to be renamed in the future, but it is okay for now. Do we have any naming for something that's either a GPA or a IOVA? > > + if (req->bad_in_num || req->bad_out_num) { > > + bool handled_unmappable = false; > > + > > + if (out_num > 2 && out_num_readable >= 2 && !req->bad_in_num && > > + out_sg[0].iov_len == sizeof(struct fuse_in_header) && > > + ((struct fuse_in_header *)fbuf.mem)->opcode == FUSE_WRITE && > > + out_sg[1].iov_len == sizeof(struct fuse_write_in)) { > > This violates the VIRTIO specification: > > 2.6.4.1 Device Requirements: Message Framing > > The device MUST NOT make assumptions about the particular arrangement of descriptors. > > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-280004 > > The driver is not obligated to submit separate iovecs. out_num == 1 is > valid and the device needs to process it byte-wise instead of making > assumptions about iovec layout. Yes, it's actually not new in this patch, but I'll clean it up. I took the shortcut all the way back in: e17f7a580e2c599330ad virtiofsd: Pass write iov's all the way through Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK