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Tsirkin" To: Denis Plotnikov Subject: Re: [PING][PING] [PATCH v4] vhost: make SET_VRING_ADDR, SET_FEATURES send replies Message-ID: <20210816074947-mutt-send-email-mst@kernel.org> References: <20210809104824.78830-1-den-plotnikov@yandex-team.ru> <14cad3d1-c99b-32ef-2aa9-803a9eb27096@yandex-team.ru> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.698, 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_H2=-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: qemu-devel@nongnu.org, yc-core@yandex-team.ru Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Aug 16, 2021 at 09:53:27AM +0300, Denis Plotnikov wrote: > > On 12.08.2021 11:04, Denis Plotnikov wrote: > > > > On 09.08.2021 13:48, Denis Plotnikov wrote: > > > On vhost-user-blk migration, qemu normally sends a number of commands > > > to enable logging if VHOST_USER_PROTOCOL_F_LOG_SHMFD is negotiated. > > > Qemu sends VHOST_USER_SET_FEATURES to enable buffers logging and > > > VHOST_USER_SET_VRING_ADDR per each started ring to enable "used ring" > > > data logging. > > > The issue is that qemu doesn't wait for reply from the vhost daemon > > > for these commands which may result in races between qemu expectation > > > of logging starting and actual login starting in vhost daemon. > > > > > > The race can appear as follows: on migration setup, qemu enables > > > dirty page > > > logging by sending VHOST_USER_SET_FEATURES. The command doesn't > > > arrive to a > > > vhost-user-blk daemon immediately and the daemon needs some time to > > > turn the > > > logging on internally. If qemu doesn't wait for reply, after sending the > > > command, qemu may start migrateing memory pages to a destination. At > > > this time, > > > the logging may not be actually turned on in the daemon but some > > > guest pages, > > > which the daemon is about to write to, may have already been transferred > > > without logging to the destination. Since the logging wasn't turned on, > > > those pages won't be transferred again as dirty. So we may end up with > > > corrupted data on the destination. > > > The same scenario is applicable for "used ring" data logging, which is > > > turned on with VHOST_USER_SET_VRING_ADDR command. > > > > > > To resolve this issue, this patch makes qemu wait for the command result > > > explicitly if VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated and > > > logging enabled. > > > > > > Signed-off-by: Denis Plotnikov This looks reasonable. This change is too scary for 6.1 so I think it should wait for 6.2. Thanks! > > > --- > > > v3 -> v4: > > >    * join acked reply and get_features in enforce_reply [mst] > > >    * typos, rewording, cosmetic changes [mst] > > > > > > v2 -> v3: > > >    * send VHOST_USER_GET_FEATURES to flush out outstanding messages > > > [mst] > > > > > > v1 -> v2: > > >    * send reply only when logging is enabled [mst] > > > > > > v0 -> v1: > > >    * send reply for SET_VRING_ADDR, SET_FEATURES only [mst] > > > --- > > >   hw/virtio/vhost-user.c | 139 +++++++++++++++++++++++++++++------------ > > >   1 file changed, 98 insertions(+), 41 deletions(-) > > > > > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > > > index ee57abe04526..5bb9254acd21 100644 > > > --- a/hw/virtio/vhost-user.c > > > +++ b/hw/virtio/vhost-user.c > > > @@ -1095,23 +1095,6 @@ static int vhost_user_set_mem_table(struct > > > vhost_dev *dev, > > >       return 0; > > >   } > > >   -static int vhost_user_set_vring_addr(struct vhost_dev *dev, > > > -                                     struct vhost_vring_addr *addr) > > > -{ > > > -    VhostUserMsg msg = { > > > -        .hdr.request = VHOST_USER_SET_VRING_ADDR, > > > -        .hdr.flags = VHOST_USER_VERSION, > > > -        .payload.addr = *addr, > > > -        .hdr.size = sizeof(msg.payload.addr), > > > -    }; > > > - > > > -    if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > > > -        return -1; > > > -    } > > > - > > > -    return 0; > > > -} > > > - > > >   static int vhost_user_set_vring_endian(struct vhost_dev *dev, > > >                                          struct vhost_vring_state *ring) > > >   { > > > @@ -1288,72 +1271,146 @@ static int vhost_user_set_vring_call(struct > > > vhost_dev *dev, > > >       return vhost_set_vring_file(dev, VHOST_USER_SET_VRING_CALL, file); > > >   } > > >   -static int vhost_user_set_u64(struct vhost_dev *dev, int request, > > > uint64_t u64) > > > + > > > +static int vhost_user_get_u64(struct vhost_dev *dev, int request, > > > uint64_t *u64) > > >   { > > >       VhostUserMsg msg = { > > >           .hdr.request = request, > > >           .hdr.flags = VHOST_USER_VERSION, > > > -        .payload.u64 = u64, > > > -        .hdr.size = sizeof(msg.payload.u64), > > >       }; > > >   +    if (vhost_user_one_time_request(request) && dev->vq_index != 0) { > > > +        return 0; > > > +    } > > > + > > >       if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > > >           return -1; > > >       } > > >   +    if (vhost_user_read(dev, &msg) < 0) { > > > +        return -1; > > > +    } > > > + > > > +    if (msg.hdr.request != request) { > > > +        error_report("Received unexpected msg type. Expected %d > > > received %d", > > > +                     request, msg.hdr.request); > > > +        return -1; > > > +    } > > > + > > > +    if (msg.hdr.size != sizeof(msg.payload.u64)) { > > > +        error_report("Received bad msg size."); > > > +        return -1; > > > +    } > > > + > > > +    *u64 = msg.payload.u64; > > > + > > >       return 0; > > >   } > > >   -static int vhost_user_set_features(struct vhost_dev *dev, > > > -                                   uint64_t features) > > > +static int vhost_user_get_features(struct vhost_dev *dev, uint64_t > > > *features) > > >   { > > > -    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features); > > > +    return vhost_user_get_u64(dev, VHOST_USER_GET_FEATURES, features); > > >   } > > >   -static int vhost_user_set_protocol_features(struct vhost_dev *dev, > > > -                                            uint64_t features) > > > +static int enforce_reply(struct vhost_dev *dev, > > > +                         const VhostUserMsg *msg) > > >   { > > > -    return vhost_user_set_u64(dev, > > > VHOST_USER_SET_PROTOCOL_FEATURES, features); > > > +    uint64_t dummy; > > > + > > > +    if (msg->hdr.flags & VHOST_USER_NEED_REPLY_MASK) { > > > +        return process_message_reply(dev, msg); > > > +    } > > > + > > > +   /* > > > +    * We need to wait for a reply but the backend does not > > > +    * support replies for the command we just sent. > > > +    * Send VHOST_USER_GET_FEATURES which makes all backends > > > +    * send a reply. > > > +    */ > > > +    return vhost_user_get_features(dev, &dummy); > > >   } > > >   -static int vhost_user_get_u64(struct vhost_dev *dev, int request, > > > uint64_t *u64) > > > +static int vhost_user_set_vring_addr(struct vhost_dev *dev, > > > +                                     struct vhost_vring_addr *addr) > > >   { > > >       VhostUserMsg msg = { > > > -        .hdr.request = request, > > > +        .hdr.request = VHOST_USER_SET_VRING_ADDR, > > >           .hdr.flags = VHOST_USER_VERSION, > > > +        .payload.addr = *addr, > > > +        .hdr.size = sizeof(msg.payload.addr), > > >       }; > > >   -    if (vhost_user_one_time_request(request) && dev->vq_index != 0) { > > > -        return 0; > > > +    bool reply_supported = virtio_has_feature(dev->protocol_features, > > > + VHOST_USER_PROTOCOL_F_REPLY_ACK); > > > + > > > +    /* > > > +     * wait for a reply if logging is enabled to make sure > > > +     * backend is actually logging changes > > > +     */ > > > +    bool wait_for_reply = addr->flags & (1 << VHOST_VRING_F_LOG); > > > + > > > +    if (reply_supported && wait_for_reply) { > > > +        msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK; > > >       } > > >         if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > > >           return -1; > > >       } > > >   -    if (vhost_user_read(dev, &msg) < 0) { > > > -        return -1; > > > +    if (wait_for_reply) { > > > +        return enforce_reply(dev, &msg); > > >       } > > >   -    if (msg.hdr.request != request) { > > > -        error_report("Received unexpected msg type. Expected %d > > > received %d", > > > -                     request, msg.hdr.request); > > > -        return -1; > > > +    return 0; > > > +} > > > + > > > +static int vhost_user_set_u64(struct vhost_dev *dev, int request, > > > uint64_t u64, > > > +                              bool wait_for_reply) > > > +{ > > > +    VhostUserMsg msg = { > > > +        .hdr.request = request, > > > +        .hdr.flags = VHOST_USER_VERSION, > > > +        .payload.u64 = u64, > > > +        .hdr.size = sizeof(msg.payload.u64), > > > +    }; > > > + > > > +    if (wait_for_reply) { > > > +        bool reply_supported = > > > virtio_has_feature(dev->protocol_features, > > > + VHOST_USER_PROTOCOL_F_REPLY_ACK); > > > +        if (reply_supported) { > > > +            msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK; > > > +        } > > >       } > > >   -    if (msg.hdr.size != sizeof(msg.payload.u64)) { > > > -        error_report("Received bad msg size."); > > > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > > >           return -1; > > >       } > > >   -    *u64 = msg.payload.u64; > > > +    if (wait_for_reply) { > > > +        return enforce_reply(dev, &msg); > > > +    } > > >         return 0; > > >   } > > >   -static int vhost_user_get_features(struct vhost_dev *dev, > > > uint64_t *features) > > > +static int vhost_user_set_features(struct vhost_dev *dev, > > > +                                   uint64_t features) > > >   { > > > -    return vhost_user_get_u64(dev, VHOST_USER_GET_FEATURES, features); > > > +    /* > > > +     * wait for a reply if logging is enabled to make sure > > > +     * backend is actually logging changes > > > +     */ > > > +    bool log_enabled = features & (0x1ULL << VHOST_F_LOG_ALL); > > > + > > > +    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features, > > > +                              log_enabled); > > > +} > > > + > > > +static int vhost_user_set_protocol_features(struct vhost_dev *dev, > > > +                                            uint64_t features) > > > +{ > > > +    return vhost_user_set_u64(dev, > > > VHOST_USER_SET_PROTOCOL_FEATURES, features, > > > +                              false); > > >   } > > >     static int vhost_user_set_owner(struct vhost_dev *dev)