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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B9F4C433DB for ; Tue, 9 Feb 2021 17:14:55 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 63CC564EC0 for ; Tue, 9 Feb 2021 17:14:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 63CC564EC0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45148 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9WbF-0004sH-AR for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 12:14:53 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48688) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9WWy-0000CR-Rz for qemu-devel@nongnu.org; Tue, 09 Feb 2021 12:10:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:37650) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9WWt-0006qu-Rj for qemu-devel@nongnu.org; Tue, 09 Feb 2021 12:10:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612890617; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iE4JY9rOsEzH8TIthOMI5icJP5DIxR53qWqU3hwutEI=; b=V3hQGhrIG0zg/XvXaNwxePq9Necj3S2tP3zOlX1HlDtxGz/wH3pU0dsYaSQ8ombZij0I/f uh+idbJzQFObPnCZL0voGb9xUS3hRe85NQTdq7nQ1FKrg2idcQPb/59n9UrgeidVHp8aef ZuFubu38bTM1zTwwZNqZ8+rnWUw2Idw= 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-26-uU_a-_e8NDS9218fRQK-dw-1; Tue, 09 Feb 2021 12:10:15 -0500 X-MC-Unique: uU_a-_e8NDS9218fRQK-dw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D3F10192D786; Tue, 9 Feb 2021 17:10:13 +0000 (UTC) Received: from gondolin (ovpn-112-148.ams2.redhat.com [10.36.112.148]) by smtp.corp.redhat.com (Postfix) with ESMTP id 95C4210016F5; Tue, 9 Feb 2021 17:10:12 +0000 (UTC) Date: Tue, 9 Feb 2021 18:10:09 +0100 From: Cornelia Huck To: Peter Maydell Subject: Re: getting the console output for s390 cdrom-test? Message-ID: <20210209181009.7f2cb328.cohuck@redhat.com> In-Reply-To: References: <5213f033-19dc-bc40-bfd7-10b8c676539b@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=170.10.133.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: Eric Farman , Thomas Huth , QEMU Developers , qemu-s390x Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 9 Feb 2021 14:58:53 +0000 Peter Maydell wrote: > On Mon, 8 Feb 2021 at 12:08, Peter Maydell wrote: > > Yes, virtio_scsi_parse_req() returns ENOTSUP because it > > fails the "if (out_size && in_size)" test. > > > > I am becoming somewhat suspicious that the s390-ccw BIOS's > > implementation of virtio is not putting in sufficient barriers, > > and so if you get unlucky then the QEMU thread sees an inconsistent > > view of the in-memory virtio data structures. > > As a test of this theory, I tried adding some barrier insns > (with the definition of the barrier insn borrowed from s390x Linux): > > diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c > index ab49840db85..0af901264b6 100644 > --- a/pc-bios/s390-ccw/virtio.c > +++ b/pc-bios/s390-ccw/virtio.c > @@ -17,6 +17,12 @@ > #include "helper.h" > #include "s390-time.h" > > +#define membarrier() do { asm volatile("bcr 15,0\n" :: : "memory"); } while (0) > + > +#define __ASM_BARRIER "bcr 15,0\n" > + > + > + > #define VRING_WAIT_REPLY_TIMEOUT 30 > > static VRing block[VIRTIO_MAX_VQS]; > @@ -154,12 +160,15 @@ void vring_send_buf(VRing *vr, void *p, int len, > int flags) > > /* Chains only have a single ID */ > if (!(flags & VRING_DESC_F_NEXT)) { > + membarrier(); > vr->avail->idx++; > + membarrier(); > } > } > > int vr_poll(VRing *vr) > { > + membarrier(); > if (vr->used->idx == vr->used_idx) { > vring_notify(vr); > yield(); > @@ -169,7 +178,9 @@ int vr_poll(VRing *vr) > vr->used_idx = vr->used->idx; > vr->next_idx = 0; > vr->desc[0].len = 0; > + membarrier(); > vr->desc[0].flags = 0; > + membarrier(); > return 1; /* vr has been updated */ > } > > This change significantly reduces the frequency with which I see > the hang; but it doesn't get rid of it altogether. Also I couldn't > really figure out from the virtio spec exactly where barriers > were required: I think I would need to read the whole thing in > more detail rather than trying to fish out the information by > just reading small pieces of it. The Linux virtio-ccw code uses 'weak barriers', i.e. the heavy bcr15 should not be needed. We might well miss other (lightweight) barriers in other parts of the code part, though. > But some of the ordering of > operations the spec describes doesn't match how the s390-ccw > BIOS code is doing it at all (eg the spec says that when feeding > a batch of descriptors to the device the driver isn't supposed to > update the flags on the first descriptor until it's finished > writing all of the descriptors, but the code doesn't seem to > try to do that). So I think the code could use an overhaul from > somebody with a better understanding of virtio than me... Yeah, the bios virtio code could probably use some love. I'm wondering how much memory ordering on the host platform influences things. I doubt many people try to run an s390x guest on an aarch64 host...