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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40DB8C433F5 for ; Mon, 4 Oct 2021 15:46:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 262B0613A1 for ; Mon, 4 Oct 2021 15:46:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235924AbhJDPrz (ORCPT ); Mon, 4 Oct 2021 11:47:55 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:40848 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235911AbhJDPry (ORCPT ); Mon, 4 Oct 2021 11:47:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633362365; 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=/kgxHPxpLf6tZjNevWzK9k9Z43+ZiXIpJpi5hdMq0z0=; b=XMRbuasuWMdRdkkTewCKD9xn++bEitVkX/DV/+ByfyKYchlmDfmeArCSWl4769uAIfAwjL nRgiDnA7cnybwZM/n7XMN1fpeSttMSWi7kLMRXh2b1FS2hERcivK5jxM4k0y/neQLvdVWZ pW7QZqXZkCeD/nVxHoo7W84KSfiSNtE= 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-263-x44U3w48N9KR2IkCHQKonA-1; Mon, 04 Oct 2021 11:46:02 -0400 X-MC-Unique: x44U3w48N9KR2IkCHQKonA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 341D58F51C; Mon, 4 Oct 2021 15:46:01 +0000 (UTC) Received: from localhost (unknown [10.39.193.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 21AE36B544; Mon, 4 Oct 2021 15:45:08 +0000 (UTC) From: Cornelia Huck To: "Michael S. Tsirkin" Cc: Halil Pasic , Jason Wang , Xie Yongji , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, markver@us.ibm.com, Christian Borntraeger , linux-s390@vger.kernel.org, virtio-dev@lists.oasis-open.org Subject: Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify In-Reply-To: <20211004110152-mutt-send-email-mst@kernel.org> Organization: Red Hat GmbH References: <20210930012049.3780865-1-pasic@linux.ibm.com> <20210930070444-mutt-send-email-mst@kernel.org> <87fstm47no.fsf@redhat.com> <20211002141351-mutt-send-email-mst@kernel.org> <20211003070030.658fc94e.pasic@linux.ibm.com> <20211003021027-mutt-send-email-mst@kernel.org> <20211003032253-mutt-send-email-mst@kernel.org> <87ee912e45.fsf@redhat.com> <20211004083455-mutt-send-email-mst@kernel.org> <878rz83lx0.fsf@redhat.com> <20211004110152-mutt-send-email-mst@kernel.org> User-Agent: Notmuch/0.32.1 (https://notmuchmail.org) Date: Mon, 04 Oct 2021 17:45:06 +0200 Message-ID: <87zgro23r1.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: > On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote: >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: >> >> > On Mon, Oct 04, 2021 at 02:01:14PM +0200, Cornelia Huck wrote: >> >> On Sun, Oct 03 2021, "Michael S. Tsirkin" wrote: >> >> > @@ -160,6 +163,33 @@ \subsection{Legacy Interface: A Note on Feature >> >> > Specification text within these sections generally does not apply >> >> > to non-transitional devices. >> >> > >> >> > +\begin{note} >> >> > +The device offers different features when used through >> >> > +the legacy interface and when operated in accordance with this >> >> > +specification. >> >> > +\end{note} >> >> > + >> >> > +Transitional drivers MUST use Devices only through the legacy interface >> >> >> >> s/Devices only through the legacy interface/devices through the legacy >> >> interface only/ >> >> >> >> ? >> > >> > Both versions are actually confused, since how do you >> > find out that device does not offer VIRTIO_F_VERSION_1? >> > >> > I think what this should really say is >> > >> > Transitional drivers MUST NOT accept VIRTIO_F_VERSION_1 through >> > the legacy interface. >> >> Ok, that makes sense. >> >> Would it make sense that transitional drivers MUST accept VERSION_1 >> through the non-legacy interface? Or is that redundant? > > We already have: > > A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. Yep, so it is redundant. > > >> > >> > >> > Does linux actually satisfy this? Will it accept VIRTIO_F_VERSION_1 >> > through the legacy interface if offered? >> >> I think that the Linux drivers will not operate on feature bit 32+ if >> they are in legacy mode? > > > Well ... with PCI there's no *way* for host to set bit 32 through > legacy. But it might be possible with MMIO/CCW. Can you tell me > what happens then? ccw does not support accessing bit 32+, either. Not sure about mmio. > > >> >> >> >> Generally, looks good to me. >> > >> > Do we want to also add explanation that features can be >> > changed until FEATURES_OK? >> >> I always considered that to be implict, as feature negotiation is not >> over until we have FEATURES_OK. Not sure whether we need an extra note. > > Well Halil here says once you set a feature bit you can't clear it. > So maybe not ... Ok, so what about something like "If FEATURES_OK is not set, the driver MAY change the set of features it accepts." in the device initialization section?