From: Marc Hartmayer <mhartmay@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.com>,
Marc Hartmayer <mhartmay@linux.ibm.com>
Cc: "Daniel P. Berrangé" <berrange@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Halil Pasic" <pasic@linux.ibm.com>,
"Stefan Hajnoczi" <stefanha@redhat.com>,
"Marc-André Lureau" <marcandre.lureau@redhat.com>
Subject: Re: [PATCH 2/2] libvhost-user: handle endianness as mandated by the spec
Date: Fri, 21 Aug 2020 10:50:30 +0200 [thread overview]
Message-ID: <87blj4fkmh.fsf@linux.ibm.com> (raw)
In-Reply-To: <20200803112626.67f55526.cohuck@redhat.com>
On Mon, Aug 03, 2020 at 11:26 AM +0200, Cornelia Huck <cohuck@redhat.com> wrote:
> On Thu, 30 Jul 2020 16:07:31 +0200
> Marc Hartmayer <mhartmay@linux.ibm.com> wrote:
>
>> Since virtio existed even before it got standardized, the virtio
>> standard defines the following types of virtio devices:
>>
>> + legacy device (pre-virtio 1.0)
>> + non-legacy or VIRTIO 1.0 device
>> + transitional device (which can act both as legacy and non-legacy)
>>
>> Virtio 1.0 defines the fields of the virtqueues as little endian,
>> while legacy uses guest's native endian [1]. Currently libvhost-user
>> does not handle virtio endianness at all, i.e. it works only if the
>> native endianness matches with whatever is actually needed. That means
>> things break spectacularly on big-endian targets. Let us handle virtio
>> endianness for non-legacy as required by the virtio specification
>> [1].
>
> Maybe add
>
> "and fence legacy virtio, as there is no safe way to figure out the
> needed endianness conversions for all cases."
Okay.
>
>> The fencing of legacy virtio devices is done in
>> `vu_set_features_exec`.
>
> Not that I disagree with fencing legacy virtio, but looking at some
> vhost-user* drivers, I'm not sure everything will work as desired for
> those (I might be missing something, though.)
>
> - vhost-user-blk lists VERSION_1 in the supported features, but
> vhost-user-scsi doesn't... is there some inheritance going on that
> I'm missing?
> - vhost-user-gpu-pci inherits from virtio-gpu-pci, so I guess it's fine
> - vhost-user-input should also always have been virtio-1
>
> So, has anybody been using vhost-user-scsi and can confirm that it
> still works, or at least can be made to work?
Unfortunately, I don’t have the required hardware :/ Can please anybody
verify this?
>
>>
>> [1] https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-210003
>>
>> Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> ---
>> contrib/libvhost-user/libvhost-user.c | 77 +++++++++++++++------------
>> 1 file changed, 43 insertions(+), 34 deletions(-)
>
> The code change per se LGTM.
Thanks for the feedback!
>
--
Kind regards / Beste Grüße
Marc Hartmayer
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Gregor Pillen
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
next prev parent reply other threads:[~2020-08-21 8:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 14:07 [PATCH 0/2] Enable virtio-fs on s390x Marc Hartmayer
2020-07-30 14:07 ` [PATCH 1/2] virtio: add vhost-user-fs-ccw device Marc Hartmayer
2020-07-30 15:19 ` Cornelia Huck
2020-07-30 14:07 ` [PATCH 2/2] libvhost-user: handle endianness as mandated by the spec Marc Hartmayer
2020-08-02 5:13 ` Michael S. Tsirkin
2020-08-03 14:17 ` Marc Hartmayer
2020-08-03 9:26 ` Cornelia Huck
2020-08-21 8:50 ` Marc Hartmayer [this message]
2020-08-02 5:13 ` [PATCH 0/2] Enable virtio-fs on s390x Michael S. Tsirkin
2020-08-04 11:29 ` Dr. David Alan Gilbert
2020-08-27 12:19 ` Michael S. Tsirkin
2020-08-27 12:26 ` Cornelia Huck
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