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bh=aH/VQW1xvhwx+OLhPcdcMoOIq5rM94XFY2M444mzjF4=; b=Xef8ZnEpPfd95V4AQawYLJjAuMagZBjDr3Lj0ZXgXFmc4YOOb5m+8KHDVtUI8HAxzHm0U8 zH7x+pS1jhLUUHOGabdU2QYEG1/BqyVpkxxrRDU/S351x4H1aRhkXIiyWhRX7x3cZfmy85 1UPMLAV8lWY7oiI9t7cQtZfGQrf5kmQ= 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-114-XWPIYyF9MeiTW8gA2beVDg-1; Tue, 16 Feb 2021 06:48:02 -0500 X-MC-Unique: XWPIYyF9MeiTW8gA2beVDg-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 8ADE9C292; Tue, 16 Feb 2021 11:48:01 +0000 (UTC) Received: from gondolin (ovpn-113-145.ams2.redhat.com [10.36.113.145]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5B7AF5C1B4; Tue, 16 Feb 2021 11:48:00 +0000 (UTC) Date: Tue, 16 Feb 2021 12:47:57 +0100 From: Cornelia Huck To: Thomas Huth Subject: Re: [PATCH] pc-bios/s390-ccw: Use memory barriers in virtio code Message-ID: <20210216124757.4eb664e9.cohuck@redhat.com> In-Reply-To: <20210216110056.1228582-1-thuth@redhat.com> References: <20210216110056.1228582-1-thuth@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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=63.128.21.124; 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_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: Christian Borntraeger , qemu-s390x@nongnu.org, qemu-devel@nongnu.org, Peter Maydell Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 16 Feb 2021 12:00:56 +0100 Thomas Huth wrote: > According to the virtio specification, a memory barrier should be > used before incrementing the idx field in the "available" ring. > So far, we did not do this in the s390-ccw bios yet, but recently > Peter Maydell saw problems with the s390-ccw bios when running > the qtests on an aarch64 host (the bios panic'ed with the message: > "SCSI cannot report LUNs: response VS RESP=09"), which could > maybe be related to the missing memory barriers. Thus let's add > those barriers now. Since we've only seen the problem on TCG so far, > a "bcr 14,0" should be sufficient here to trigger the tcg_gen_mb() > in the TCG translate code. > > (Note: The virtio spec also talks about using a memory barrier > *after* incrementing the idx field, but if I understood correctly > this is only required when using notification suppression - which > we don't use in the s390-ccw bios here) > > Signed-off-by: Thomas Huth > --- > pc-bios/s390-ccw/virtio-net.c | 1 + > pc-bios/s390-ccw/virtio.c | 1 + > pc-bios/s390-ccw/virtio.h | 2 ++ > 3 files changed, 4 insertions(+) > > diff --git a/pc-bios/s390-ccw/virtio-net.c b/pc-bios/s390-ccw/virtio-net.c > index 2fcb0a58c5..25598a7a97 100644 > --- a/pc-bios/s390-ccw/virtio-net.c > +++ b/pc-bios/s390-ccw/virtio-net.c > @@ -127,6 +127,7 @@ int recv(int fd, void *buf, int maxlen, int flags) > > /* Mark buffer as available to the host again */ > rxvq->avail->ring[rxvq->avail->idx % rxvq->num] = id; > + virtio_mb(); > rxvq->avail->idx = rxvq->avail->idx + 1; > vring_notify(rxvq); > > diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c > index ab49840db8..fb9687f9b3 100644 > --- a/pc-bios/s390-ccw/virtio.c > +++ b/pc-bios/s390-ccw/virtio.c > @@ -154,6 +154,7 @@ void vring_send_buf(VRing *vr, void *p, int len, int flags) > > /* Chains only have a single ID */ > if (!(flags & VRING_DESC_F_NEXT)) { > + virtio_mb(); I think you need to also need barriers for changes to the buffers, as the spec talks about "manipulating the descriptor table". > vr->avail->idx++; > } > } > diff --git a/pc-bios/s390-ccw/virtio.h b/pc-bios/s390-ccw/virtio.h > index 19fceb6495..6ac65482a9 100644 > --- a/pc-bios/s390-ccw/virtio.h > +++ b/pc-bios/s390-ccw/virtio.h > @@ -271,6 +271,8 @@ struct VirtioCmd { > }; > typedef struct VirtioCmd VirtioCmd; > > +#define virtio_mb() asm volatile("bcr 14,0" : : : "memory") The bios is built for z900, so you probably need a bcr15 here? > + > bool vring_notify(VRing *vr); > int drain_irqs(SubChannelId schid); > void vring_send_buf(VRing *vr, void *p, int len, int flags);