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bh=VWvrs3yQ9kZPxKF4Fz4oEyIhuqvOitjo0W/J7v7is+g=; b=OSDfBq14xWvbtglvoC1RoPgf+bfYtrlfWomqmVFv6fWeef9ijesJoVf2YITOvStlLxjzUK Hllp3Vdb7v7PgVkMMPM+a0MlrRa7ifXTq+AvfDwsgdTm9wD9CtcaUPpX03S4KhFkvyp86l PLdkq/E86aVYAwU3XmTq2toKoQgCDJo= 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-495-8ePL1qwdOEGwUuAlsNpIzg-1; Tue, 16 Feb 2021 09:50:07 -0500 X-MC-Unique: 8ePL1qwdOEGwUuAlsNpIzg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CDB6587124A; Tue, 16 Feb 2021 14:50:01 +0000 (UTC) Received: from gondolin (ovpn-113-145.ams2.redhat.com [10.36.113.145]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9A6D460C9B; Tue, 16 Feb 2021 14:50:00 +0000 (UTC) Date: Tue, 16 Feb 2021 15:49:57 +0100 From: Cornelia Huck To: Peter Maydell Subject: Re: [PATCH] pc-bios/s390-ccw: Use memory barriers in virtio code Message-ID: <20210216154957.1cc0afdf.cohuck@redhat.com> In-Reply-To: References: <20210216110056.1228582-1-thuth@redhat.com> <20210216124757.4eb664e9.cohuck@redhat.com> <20210216153003.16b05725.cohuck@redhat.com> <5765bde0-f222-4b07-25d4-430b101ef8ff@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Christian Borntraeger , Thomas Huth , qemu-s390x , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 16 Feb 2021 14:37:22 +0000 Peter Maydell wrote: > On Tue, 16 Feb 2021 at 14:35, Thomas Huth wrote: > > > > On 16/02/2021 15.32, Peter Maydell wrote: > > > On Tue, 16 Feb 2021 at 14:30, Cornelia Huck wrote: > > >> Step 4 in "2.7.13 Supplying Buffers to The Device": > > >> > > >> "The driver performs a suitable memory barrier to ensure the device > > >> sees the updated descriptor table and available ring before the next > > >> step." > > > > > > I thought that my first time through the spec as well, but > > > I think the whole of section 2.7 is dealing with "packed virtqueues", > > > which have to be explicitly negotiated and which I don't think > > > the s390-ccw code is doing. 2.7 is split, 2.8 packed (at least in my built-from-git version; maybe I should have mentioned that :) > > > > Right. I think the s390-ccw code is still based on virtio v1.0, that's why I > > also only looked at that version of the spec. Yes, the bios code is using split. > I think the ideal would be to find somebody who's really well > acquainted with the virtio spec (MST?) and ask them to have > a quick look-over the s390-ccw code to say where it needs > changes... The fact that this patch doesn't completely fix > the bug leaves me suspicious that we're missing something in > our readings of the spec. Unfortunately, the bios virtio code is not that easy to follow :/