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Thu, 7 Oct 2021 15:52:45 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B6A7EA405B; Thu, 7 Oct 2021 15:52:45 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D7ADEA406A; Thu, 7 Oct 2021 15:52:44 +0000 (GMT) Received: from li-e979b1cc-23ba-11b2-a85c-dfd230f6cf82 (unknown [9.171.45.119]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with SMTP; Thu, 7 Oct 2021 15:52:44 +0000 (GMT) Date: Thu, 7 Oct 2021 17:52:42 +0200 From: Halil Pasic To: Cornelia Huck Subject: Re: [PATCH 1/1] virtio: write back F_VERSION_1 before validate Message-ID: <20211007175242.4b0155b8.pasic@linux.ibm.com> In-Reply-To: <8735pczwjj.fsf@redhat.com> References: <20211006142533.2735019-1-pasic@linux.ibm.com> <875yu9yruv.fsf@redhat.com> <20211007163255.61d95513.pasic@linux.ibm.com> <8735pczwjj.fsf@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 8qM-a0uJ38LmRa_8qRQ5tnNtExH-AgEu X-Proofpoint-GUID: mZZoBXl8LjQNHDs4rEn3GtR4FOFRoEZK X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.182.1,Aquarius:18.0.790,Hydra:6.0.391,FMLib:17.0.607.475 definitions=2021-10-07_02,2021-10-07_02,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 suspectscore=0 lowpriorityscore=0 mlxscore=0 clxscore=1015 bulkscore=0 impostorscore=0 phishscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109230001 definitions=main-2110070101 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pasic@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H4=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: linux-s390@vger.kernel.org, markver@us.ibm.com, "Michael S. Tsirkin" , Jason Wang , qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Halil Pasic , Xie Yongji , Raphael Norwitz , stefanha@redhat.com, virtualization@lists.linux-foundation.org, Christian Borntraeger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 07 Oct 2021 17:25:52 +0200 Cornelia Huck wrote: > On Thu, Oct 07 2021, Halil Pasic wrote: > > > On Thu, 07 Oct 2021 13:52:24 +0200 > > Cornelia Huck wrote: > > > >> On Wed, Oct 06 2021, Halil Pasic wrote: > >> > >> > The virtio specification virtio-v1.1-cs01 states: "Transitional devices > >> > MUST detect Legacy drivers by detecting that VIRTIO_F_VERSION_1 has not > >> > been acknowledged by the driver." This is exactly what QEMU as of 6.1 > >> > has done relying solely on VIRTIO_F_VERSION_1 for detecting that. > >> > > >> > However, the specification also says: "... driver MAY read (but MUST NOT > >> > write) the device-specific configuration fields to check that it can > >> > support the device ..." before setting FEATURES_OK. > >> > >> Suggest to put the citations from the spec into quotes, so that they are > >> distinguishable from the rest of the text. > > > > For the record: I basically took Michael's description, the one which you > > said you prefer, with some minor changes. > > Well I did look at what the text said, not the details in the formatting... > > > > > This is one of the changes, which renders this a paraphrase and not a > > quote. Michael didn't use quotation marks so I was not sure it is was > > a word by word quote anyway. It was. But the spec depends on "During this > > step" which does not make any sense without the context. That is why I made > > the end of step explicit. > > I still think that would be nicer while using some quotation marks, even > if you are just doing a partial quote. > > In the first paragraph, however, we really should mark the quote > properly. It gave me a stop when I first read it. I've added in some quotation marks and ellipsis marks. Does that look good for you? > > > > > I think we are fine without quotation marks. Those who care can read the > > spec. > > > >> > >> > > >> > In that case, any transitional device relying solely on > >> > VIRTIO_F_VERSION_1 for detecting legacy drivers will return data in > >> > legacy format. In particular, this implies that it is in big endian > >> > format for big endian guests. This naturally confuses the driver which > >> > expects little endian in the modern mode. > >> > > >> > It is probably a good idea to amend the spec to clarify that > >> > VIRTIO_F_VERSION_1 can only be relied on after the feature negotiation > >> > is complete. However, we already have regression so let's try to address > >> > >> s/regression/a regression/ > >> > > > > Yes. Was like this in the original. Will change > > > >> > it. > >> > >> Maybe mention what the regression is? > > > > How about the following? > > > > The regressions affect the VIRTIO_NET_F_MTU feature of virtio-net and the > > VIRTIO_BLK_F_BLK_SIZE feature of virtio-blk for BE guests when virtio > > 1.0 is used on both sides. The latter renders virtio-blk unusable with > > DASD backing, because things simply don't work with the default. > > Sounds good to me. Will add it to the end. > > > > >> > >> Also mention that we use this workaround for modern on BE only? > > > > We have that already, don't we. The sentence that starts with "In > > particular". The regression description should reinforce that > > sufficiently IMHO. > > No strong opinion here. Anyone else? > > > > >> > >> > > >> > Signed-off-by: Halil Pasic > >> > Fixes: 82e89ea077b9 ("virtio-blk: Add validation for block size in config space") > >> > Fixes: fe36cbe0671e ("virtio_net: clear MTU when out of range") > >> > Reported-by: markver@us.ibm.com > >> > --- > >> > drivers/virtio/virtio.c | 10 ++++++++++ > >> > 1 file changed, 10 insertions(+) > >> > > >> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > >> > index 0a5b54034d4b..494cfecd3376 100644 > >> > --- a/drivers/virtio/virtio.c > >> > +++ b/drivers/virtio/virtio.c > >> > @@ -239,6 +239,16 @@ static int virtio_dev_probe(struct device *_d) > >> > driver_features_legacy = driver_features; > >> > } > >> > > >> > + /* > >> > + * Some devices detect legacy solely via F_VERSION_1. Write > >> > + * F_VERSION_1 to force LE for these when needed. > >> > >> "...to force LE config space accesses before FEATURES_OK for these when > >> needed (BE)." > >> > >> ? > > > > Can do, but I would rather omit the (BE) at the end. All the conditions > > are necessary: > > * have validate callback > > * device offered VERSION_1 > > * virtio legacy is be > > > > Ok, let's use that without the trailing BE. > Nod. > >> > >> > + */ > >> > + if (drv->validate && !virtio_legacy_is_little_endian() > >> > + && BIT_ULL(VIRTIO_F_VERSION_1) & device_features) { > >> > >> Nit: putting device_features first would read more naturally to me. > >> > > > > Can do. > > > >> > + dev->features = BIT_ULL(VIRTIO_F_VERSION_1); > >> > + dev->config->finalize_features(dev); > >> > + } > >> > + > >> > if (device_features & (1ULL << VIRTIO_F_VERSION_1)) > >> > dev->features = driver_features & device_features; > >> > else > >> > >> Patch LGTM. > >> > >> > > > > Thanks for having a look. If you are fine with the proposed solution > > please tell me, so I can send out a v2. > > No further comments other than what I wrote above, but maybe others have > comments as well? > > I will wait then till end of day before sending out a v2. Thank you very much! Regards, Halil