From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34264 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726882AbgDXNDC (ORCPT ); Fri, 24 Apr 2020 09:03:02 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 03OCqF7G142290 for ; Fri, 24 Apr 2020 09:03:01 -0400 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 30k7rn78xm-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 24 Apr 2020 09:03:00 -0400 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 24 Apr 2020 14:02:21 +0100 Date: Fri, 24 Apr 2020 15:02:40 +0200 From: Halil Pasic Subject: Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD In-Reply-To: <20200420141317.4537498f.cohuck@redhat.com> References: <20200417182939.11460-1-jrossi@linux.ibm.com> <20200417182939.11460-2-jrossi@linux.ibm.com> <20200420141317.4537498f.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Message-Id: <20200424150240.6fdede81.pasic@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Cornelia Huck Cc: Jared Rossi , Eric Farman , linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, 20 Apr 2020 14:13:17 +0200 Cornelia Huck 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... my understanding is that we have the reasonable expectation that > our guests will always issue channel programs that work fine with > prefetch even if the bit is not set in the orb (including CCW IPL, in > the way it is implemented in the s390-ccw QEMU bios), and therefore > this patch is just making things less complicated. AFAIR the problem is not s390-ccw QEMU bios. We could easily fix that. The practical problem is some channel programs generated by zipl that simply fail to set the bit (although they could). That is a perfectly legit thing to do, because the prefetch bit was originally about performance. Sorry I missed your mail, so complained about the same issues. Regards, Halil