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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 BED72C54FD0 for ; Thu, 23 Apr 2020 15:11:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98E9420857 for ; Thu, 23 Apr 2020 15:11:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LSeysXyx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729043AbgDWPLS (ORCPT ); Thu, 23 Apr 2020 11:11:18 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:31540 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728878AbgDWPLR (ORCPT ); Thu, 23 Apr 2020 11:11:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587654676; 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=p98rCYJhtZR44ScMt2ctfYRg4qGKkTUSrXSjyzpvnXo=; b=LSeysXyx17f58+nkjrqsUkdtjnW9ET3yHrQZrirfGifdbvrtIZ/mlysEyBjMCRBiBB6rJj i70FDlyBFnXzB3JGwoLzujcggZ/7X+f2nDjs3ZoVMwDHFsAlnQN7FCsQx+H1+dOsjdyQ/U YYdsREitGgYJCpcLX8JRN1bgQnDsqvk= 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-184-O4prfYliPcqdEkCRMS9Erg-1; Thu, 23 Apr 2020 11:11:09 -0400 X-MC-Unique: O4prfYliPcqdEkCRMS9Erg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4E7E3872FF0; Thu, 23 Apr 2020 15:11:08 +0000 (UTC) Received: from gondolin (ovpn-112-121.ams2.redhat.com [10.36.112.121]) by smtp.corp.redhat.com (Postfix) with ESMTP id D0E8D600F5; Thu, 23 Apr 2020 15:11:06 +0000 (UTC) Date: Thu, 23 Apr 2020 17:11:03 +0200 From: Cornelia Huck To: Halil Pasic Cc: Jared Rossi , Eric Farman , linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD Message-ID: <20200423171103.497dcd02.cohuck@redhat.com> In-Reply-To: <20200423155620.493cb7cb.pasic@linux.ibm.com> References: <20200417182939.11460-1-jrossi@linux.ibm.com> <20200417182939.11460-2-jrossi@linux.ibm.com> <20200423155620.493cb7cb.pasic@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 23 Apr 2020 15:56:20 +0200 Halil Pasic wrote: > On Fri, 17 Apr 2020 14:29:39 -0400 > Jared Rossi wrote: > > > Remove the explicit prefetch check when using vfio-ccw devices. > > This check is not needed as all Linux channel programs are intended > > to use prefetch and will be executed in the same way regardless. > > Hm. This is a guest thing or? So you basically say, it is OK to do > this, because you know that the guest is gonna be Linux and that it > the channel program is intended to use prefetch -- but the ORB supplied > by the guest that designates the channel program happens to state the > opposite. > > Or am I missing something? I see this as a kind of architecture compliance/ease of administration tradeoff, as we none of the guests we currently support uses something that breaks with prefetching outside of IPL (which has a different workaround). One thing that still concerns me a bit is debuggability if a future guest indeed does want to dynamically rewrite a channel program: the guest thinks it instructed the device to not prefetch, and then suddenly things do not work as expected. We can log when a guest submits an orb without prefetch set, but we can't find out if the guest actually does something that relies on non-prefetch. The only correct way to handle this would be to actually implement non-prefetch processing, where I would not really know where to even start -- and then we'd only have synthetic test cases, for now. None of the options are pleasant :(