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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 CF7FDC433DB for ; Mon, 15 Feb 2021 11:49:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9C45B64DFD for ; Mon, 15 Feb 2021 11:49:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230117AbhBOLso (ORCPT ); Mon, 15 Feb 2021 06:48:44 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42021 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230120AbhBOLsg (ORCPT ); Mon, 15 Feb 2021 06:48:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613389629; 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=D22s3OuQqHDBBIq03XJttdJ4KRGjRR6pC+JhDOVlOkU=; b=TDGsJ949jBseFKP6fQWYQ4ItTPjlLEjEIGJDLqcu0Cz2Slrwe3v6VgGGLttz1c9tgzXtPd z3tvnrSpcne4eKhEVvGOWuNQUz4VZ4/bgzHrbYTQUt0CNgkTXHyYa2I6PLlX8a6fRhUP6n NttjlsewznBQrxxnc7C/M8PNlcbpvMk= 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-167-sJoUwJx-PS2WINi8H1HfSw-1; Mon, 15 Feb 2021 06:47:07 -0500 X-MC-Unique: sJoUwJx-PS2WINi8H1HfSw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 44288100CCC1; Mon, 15 Feb 2021 11:47:06 +0000 (UTC) Received: from gondolin (ovpn-113-55.ams2.redhat.com [10.36.113.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id DDBD75C3F8; Mon, 15 Feb 2021 11:47:04 +0000 (UTC) Date: Mon, 15 Feb 2021 12:47:02 +0100 From: Cornelia Huck To: Halil Pasic Cc: Pierre Morel , linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Subject: Re: [PATCH] virtio/s390: implement virtio-ccw revision 2 correctly Message-ID: <20210215124702.23a093b8.cohuck@redhat.com> In-Reply-To: <20210212170411.992217-1-cohuck@redhat.com> References: <20210212170411.992217-1-cohuck@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, 12 Feb 2021 18:04:11 +0100 Cornelia Huck wrote: > CCW_CMD_READ_STATUS was introduced with revision 2 of virtio-ccw, > and drivers should only rely on it being implemented when they > negotiated at least that revision with the device. > > However, virtio_ccw_get_status() issued READ_STATUS for any > device operating at least at revision 1. If the device accepts > READ_STATUS regardless of the negotiated revision (which it is > free to do), So, looking at the standard again, the device is actually required to reject the READ_STATUS if only rev 1 had been negotiated... regardless of that, I don't think we should change QEMU's behaviour, as it would affect existing guests (they would lose access to the status bits as observed by the device, including DEVICE_NEEDS_RESET.) > everything works as intended; a device rejecting the > command should also be handled gracefully. For correctness, we > should really limit the command to revision 2 or higher, though. > > We also negotiated the revision to at most 1, as we never bumped > the maximum revision; let's do that now. > > Fixes: 7d3ce5ab9430 ("virtio/s390: support READ_STATUS command for virtio-ccw") > Signed-off-by: Cornelia Huck > --- > > QEMU does not fence off READ_STATUS for revisions < 2, which is probably > why we never noticed this. I'm not aware of other hypervisors that do > fence it off, nor any that cannot deal properly with an unknown command. > > Not sure whether this is stable worthy? Maybe it is, given the MUST reject clause in the standard? > > --- > drivers/s390/virtio/virtio_ccw.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c > index 5730572b52cd..54e686dca6de 100644 > --- a/drivers/s390/virtio/virtio_ccw.c > +++ b/drivers/s390/virtio/virtio_ccw.c > @@ -117,7 +117,7 @@ struct virtio_rev_info { > }; > > /* the highest virtio-ccw revision we support */ > -#define VIRTIO_CCW_REV_MAX 1 > +#define VIRTIO_CCW_REV_MAX 2 > > struct virtio_ccw_vq_info { > struct virtqueue *vq; > @@ -952,7 +952,7 @@ static u8 virtio_ccw_get_status(struct virtio_device *vdev) > u8 old_status = vcdev->dma_area->status; > struct ccw1 *ccw; > > - if (vcdev->revision < 1) > + if (vcdev->revision < 2) > return vcdev->dma_area->status; > > ccw = ccw_device_dma_zalloc(vcdev->cdev, sizeof(*ccw));